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Arsenic in Aquatic Macrophytes: Concentrations in the Wailuku and Wailoa Watersheds

Final Report

April 2012

Principal Investigators: Kim Falinski and Russell Yost, University of Hawai’i

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Table of Contents Introduction ......................................................................................................................... 3

Arsenic Studies in the Hilo area ...................................................................................... 4 Chemistry of Arsenic ...................................................................................................... 5

Reduced conditions may lead to arsenic release ......................................................... 5 Aquatic plants as hyperaccumulators.......................................................................... 5

Goals and Objectives: ......................................................................................................... 7 Methods: ............................................................................................................................. 8

Field work and site description ....................................................................................... 8 Soil collection ................................................................................................................. 8 Sediment collection ......................................................................................................... 8 Sample analysis ............................................................................................................... 8 Plant collection and analysis ........................................................................................... 9 Protocol for sample collection with Erica Sampaga and Keanu Pinner ....................... 10

Results: .............................................................................................................................. 11 GIS ................................................................................................................................ 11 Soil samples .................................................................................................................. 11 Plant samples ................................................................................................................ 11 Sediment samples.......................................................................................................... 12

Discussion ......................................................................................................................... 12 Arsenic distribution and potential sources .................................................................... 12 Arsenic in plants grown in flooded conditions ............................................................. 13

Conclusions ....................................................................................................................... 14 Acknowledgements ........................................................................................................... 15 Figures and Tables ............................................................................................................ 16 References ......................................................................................................................... 30

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Introduction

Arsenic-based herbicides, mostly in the form of sodium arsenite, were used extensively on sugar cane plantations for weed control in the Hilo, Hawai`i, area in the early to mid- twentieth century before being replaced by pentachlorophenol formulations, phenoxy and triazinine herbicides, and then other types of herbicides. Today, arsenic contaminated soil continues to be found on former sugar cane land in levels that are significantly above background levels. The full risk of arsenic contamination, especially in eastern Hawai'i, is unknown.

The health risk due to arsenic contact has been documented extensively ((NTP 2011)1980; (Wu, Kuo et al. 1989)Wu, 1989). Arsenic is considered a priority pollutant by U.S. Environmental Protection Agency (EPA). it has been found at over 60% of U.S. National Priorities List sites, and it is the most common contaminant metal at U.S. Department of Defense sites. In high concentrations, it is toxic to ecosystems and humans, especially in inorganic forms such as arsenate and arsenite salts. Chronic exposure to As has been shown to cause a variety of cancers and health problems (Wu, Kuo et al. 1989), and in rare cases can lead to death through organ failure. It is considered a known carcinogen by the EPA. New studies have shown that elevated arsenic soil concentrations, in conjunction with lead levels, can impair mental development, even in total As levels as low as 22 mg/kg (McDermott, Wu et al. 2011)).

The national EPA standard for total arsenic in drinking water is 10 μg/L, while there remains no maximum contaminant level in soils or in food. The global average for arsenic in soils is 5 mg/kg ((IARC 2004)). The Hawai'i Department of Health (HDOH) action level for total As in soils is 24 mg/kg (for the <2mm size fraction) for total arsenic, which triggers further evaluation and determination of the bioaccessible arsenic levels using a laboratory assay method. and 23 mg/kg for bioaccessible arsenic to begin remediation (for the <250 μm soil size fraction). For food, the EPA standard is 0.3 μg/kg/day, which is approximately 21 μg/day for a 70 kg adult. It is currently estimated that intake from food, especially rice and fish, already accounts for 44 μg/day, far exceeding the limit (Brewer 2011).

There are a number of possible routes of exposure. Arsenic found dissolved in water is toxic at low levels if ingested. This is particularly a concern in countries like Bangladesh, where arsenic has accumulated due to natural origin. Exposure from contaminated soil can occur through ingestion, breathing, skin absorption or having dust enter the eyes. Children, home gardeners and farmworkers are at the greatest risk of exposure through these pathways. Lastly, food contamination by arsenic is possible.

On the Big Island of Hawai'i, the risk of exposure to contaminated soil has been thought to be most likely through inadvertent soil ingestion. Skin absorption or the inhalation of contaminated soil is believed to very minor routes of exposure compared to soil ingestion. Testing of garden vegetable and fruits have revealed levels of arsenic similar to U.S. FDA market basket survey data (HDOH 2007), so inadvertent soil ingestion (e.g. transfer of soil on hands or from root vegetables not well washed) is believed to be the primary exposure route. Arsenic contamination of groundwater in Hawai`i has not been documented in many years of testing of public drinking water supplies. New development, including housing, schools and government buildings, seeks to re-appropriate former sugar cane land for residential and commercial use, while

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some former sugar cane land is being used again for different types of agricultural practices (Niemeyer 2011). Although arsenic is not very mobile in the soil due to its strong bonds with iron oxides, it is possible for arsenic to accumulate and be transported through physical processes such as erosion (Cadwalader, Renshaw et al. 2011).

There is increased awareness of possible food contamination. Recent research suggests that aquatic macrophytes such as watercress and taro may be accumulators of arsenic (Zhao, McGrath et al. 2010). While in general, if arsenic is mobilized because of reduced conditions in hypoxic or anoxic flooded fields, it becomes possible for aquatic plants to take up the dissolved inorganic arsenic. Environmental conditions, physical and chemical properties of the soil and modifications to the soil in the rhizosphere interact to influence the plant availability of arsenic. Ratios of plant available arsenic to total arsenic may increase under reduced conditions that result in reduction and solubilization of iron oxides, and reduction of arsenate to the more soluble arsenite ((Zhao, McGrath et al. 2010)). Arsenate is usually present in very low levels in soil solution, but arsenite may be mobilized into the soil solution if the field is submerged.

Several other analyses of arsenic in soils or sediment are often used to assess exposure and risk. The bioavailability of arsenic is assessed by animal testing. Very little information is known about the effects of different soil properties on bioavailability[GM1]. The related bioaccessible arsenic evaluation estimates bioavailability through the use of laboratory assays, and is used to assess action levels for soils (Hughes, Kenyon et al. 2003 El-Masri and Kenyon 2008, Bradham, Scheckel et al. 2011; Cutler 2011; Juhasz, Weber et al. 2011).

Our sampling and detection strategy was to first sample potential locations where As may have accumulated using measures of total As. Such a strategy will give a maximum amount of information since some total As is nearly always present in soils with high levels of short-range order iron and aluminum oxides. The accompanying sampling and measurement of plant As was designed to detect whether the high levels of total As previously detected in some samples may be appearing in eatable plants, especially aquatic plants where total As or bioaccessible As ratios may differ from those in aerobic soils. This report, therefore, concentrates on the measurement of total arsenic in soils and plants.

Arsenic Studies in the Hilo area In Hawai‘i, arsenic is typically found at natural occurring background concentrations

in soil of less than 24 mg kg-1 (HDOH 2012). However, significantly elevated levels have been identified in a number of locations in the Hilo and Puna districts of East Hawai'i (HDOH 2006; Cutler 2011). Concentrations of total arsenic in soils from undeveloped former sugar cane lands in the Kea’au area (Puna district) have been reported to range from 100-400 mg kg-1 in the <2 mm size fraction of the soil and >500 mg kg-1 in the <250 μm size fraction (Ortiz-Escobar 2006; HDOH 2007). When speciation was reported in the Kea’au studies (N=26), arsenic was mostly present as arsenate, indicating an oxidizing environment. The soils in this study were Hydrudands, indicating extreme weathering and extremely high capacities to sorb phosphorus.

Waiakea Pond, an estuary that is formed between the Wailoa river and Hilo Bay, has been studied with regards to arsenic. A canec plant located on its banks formerly dumped arsenic-based pesticides into the estuary. It has been reported to have total arsenic

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concentrations in its sediments up to 10,583 mg kg-1 ((Hallacher, Kho et al. 1985; Glendon-Baclig 2007)Kho, 1991). A study of the flora and fauna in the pond showed that there was no detectable arsenic in Elodea sp. and blue-green algae, but measurable amounts (1.3 mg/kg) were found in the tissues of fish and crabs (Hallacher et al., 1985; HDOH, 2005).

Testing of produce from community gardens in the Ke’eau area in 2005 by the Hawai`i Department of Health showed only marginally elevated arsenic concentrations, especially in root crops, as compared to typical market produce published by the Food and Drug Administration. Analysis of certain garden soils revealed a higher arsenic bioaccessibility than in soils from the surrounding non-garden. The addition of fertilizers or soil conditioning agents intended to make nutrients more available to plants was suggested as one possible cause of the higher arsenic found in the gardens.

In early 2011, a student at Hilo High School conducted a study at a watercress field in Kaumana Springs, outside Hilo. The area is known for its artesian springs, which feed oxygenated water to the fields. After analysis at the University of Hawai`i at Hilo by EDXRF with Dr. Steve Lundblad, she reported extremely high arsenic concentrations in the soils next to the field, up to 1000 mg kg-1 ((Pinner 2011)). Because watercress is generally grown in very moist soil or directly in clean oxygenated water, there is potential for arsenic to be released from the soil or sediment and taken up by the plants. The Kaumana Springs results have yet to be validated and extended.

Chemistry of Arsenic

Reduced conditions may lead to arsenic release There have been two identified triggers of arsenic release: first, high pH in arid or

estuarine environments and second, reduced conditions at neutral or near-neutral pH (Smedley and Kinniburgh 2002). In the iron-rich soils of Hawai’i, it is likely that under oxic conditions, arsenic is sorbed to iron particles and not very mobile ((Livesey and Huang 1981; Bowell 1994)). Reductive dissolution of iron (oxy)hydroxides releases sorbed arsenic, allowing for absorption by plants, a process mediated biologically by bacterial communities or in the rhizosphere of plants. AfterOn uptake, plantsMicroorganisms can then convert the inorganic arsenicarsenite in the soil solution by biomethylation to arsenosugars including monomethyarsenous acid (MMA) and dimethylarsenic acid (DMA) (Zhao, McGrath et al. 2010).

There is evidence that soil characteristics directly correlate with variation in arsenic and lead concentrations in vegetables and fruit (Bacigalupo and Hale 2011)(Bacigalupo et al, 2011). Studies have shown that there is only a weak correlation between total arsenic concentration and bioaccessibile arsenic (Munier, 2010{Anawar, 2008 #3740}(Anawar, Garcia-Sanchez et al. 2008)). The soil substrate, mineralogy and redox conditions are likely to play an important role in the toxicity of arsenic to higher organisms.

Aquatic plants as hyperaccumulators Arsenic can be taken up inadvertently in aquatic plants using pathways for phosphate

absorption, and then either bio-accumulated or bio-transformed into a less toxic form such as MMA or DMA. Arsenic concentrations up to four or five orders of magnitude

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greater than the surrounding soil concentrations have been found in plant, fungal and algal tissues ((Rahman, Hasegawa et al. 2007; Rahman, Hasegawa et al. 2007; Francesconi 2010)). A hyperaccumulator is defined as a plant species that can have concentrations up toaccumulate more than 1,000 mg/kg in their above-ground tissues without suffering phytotoxicity ((Zhao, Dunham et al. 2002; Zhao, McGrath et al. 2010). ref. needed). A well-known hyperaccumulator is the Chinese brake ferm (Pteris vittata), which has been shown to accumulate up to 23,000 mg/kg total arsenic (ref needed(Ma, Komar et al. 2001)). Older fronds had the most arsenic.

It is known that tThe toxic effects of arsenic depend on the chemical form of its compounds occurring in living organisms ((Chancho, Sanchez et al. 2010)). Most of the arsenic occurs in its organic form, which is much less toxic to humans than the inorganic form (Schoof, Yost et al. 1999)(ref needed). Although scientists are not entirely sure how inorganic arsenic is transformed to organic arsenic, it is known that the oxidation statespeciation of the inorganic arsenic, as arsenate (V) or arsenite (III), influences uptake by plants. In addition, iron, phosphorus, sulfur, and silicon interact strongly with arsenic during its transport and absorption from soil by plants. Plants take up arsenate through the phosphate transporters ((Zhao, McGrath et al. 2010)). Arsenite and Uundissociated methylated As species use aquaporin channels, while arsenite is taken up via the silicon pathway. Arsenate is quickly reduced to arsenite in plants, which detoxify it through complexation with thiol-rich peptides such as phytochelatins or vacuolar sequestration ((Raab, Feldmann et al. 2004; Zhao, Ma et al. 2009)).

Rice has been studied extensively because of its high consumption in Asian countries, and is an accumulator of arsenic ((Abedin, Cresser et al. 2002; Meharg and Rahman 2003)). Notably, an approximate ten-fold increase in arsenic levels in rice grown in anaerobic conditions compared to aerobic conditions was documented ((Xu, McGrath et al. 2008)).

In other aquatic plants, accumulation has also been seen. Chancho et al. (2010) describe arsenic in the seagrass Posidonia and the brown algae Durvillea and Lessonia, and reported that the accumulation varies by species. Rahman et al (2007) investigated duckweed (Spirodela polyrhiza L.), and found that the arsenic concentrations negatively correlated with phosphate uptake concentrations, and positively correlated with iron uptake concentrations. Aquatic macrophytes S. polyrhiza and Eleocharis acicularis, along with various ferns, are considered possible candidates for phytoremediation of arsenic ((Francesconi, Visoottiviseth et al. 2002; Rahman, Hasegawa et al. 2007; Ha, Sakakibara et al. 2009)).

Little research has been done on edible aquatic macrophytes. Robinson et al. ((Robinson, Outred et al. 1995) ) found arsenic levels of up to 500 mg kg-1 (dry weight) in the leaves of Ceratophyllum demersum (commonly called watercress), an aquatic, flowering plant found in a river system in New Zealand. Researchers were unable to conclude, however, whether the uptake was due to elevated concentrations of arsenic in dissolved form or in the sediments within which the watercress was grown. In a greenhouse experiment, they reported that watercress preferentially stores arsenic in its leaves rather than in the stems.

Watercress (Nasturtium officinale) is a leafy green vegetable crop grown in Hawai`i, with approximately 7850,000 lbs produced in 201008 for fresh market use (2010)02) ((Service 2010)(2010)). Most of the 35 acres dedicated to watercress production are on

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O’ahu near Pearl Harbor, in oxygenated water from artesian springs. This crop is also grown on the other Hawaiian islands for small scale commercial production or community consumption. It is traditional to grow watercress using spring water or artesian well water, but where that is unavailable, hydroponic systems can also produce a healthy crop. Consumption of watercress is assumed to be less than 100g per day per person, although this number is only an estimate. There is a substantial amount of information that points to at least some watercress as a hyperaccumulator of arsenic ((Robinson, Kim et al. 2006)).

Hawai'i is one of the few places in the United States where edible ferns are consumed by a segment of the population on a regular basis. Diplazium esculentum, the vegetable fern, known as warabi (from the Japanese), or ho'i'o or pohole (Hawaiian), is a woody fern. The fiddleheads of the warabi (Diplazium esculentum) are eaten either fresh or pickled as a delicacy on salads or in stir-frys and soups. In the US, it is only found in Hawai'i and in the Florida Everglades. In Hawai'i, warabi is available in Asian food stores and regularly at farmer's markets. It is likely that warabi is grown only semi-commercially, and is usually harvested from forest patches. Warabi is most often found in saturated soils and in or alongside transient stream beds.

Taro (Colocasia esculenta) is an important part of the cultural and agricultural tradition in Hawai`i. Four million pounds were produced in 2009 on 100 acres of land, mostly in Hawai’i and Kaua’i. There is little information available for the processes that may lead to the accumulation of arsenic in wetland taro plants. In Bangladesh, researchers found a correlation between soil arsenic and dryland taro leaf concentrations, with up to 0.63 mg kg-1 in the leaf ((Kurosawa, Egashira et al. 2008)). It is expected that concentrations would be higher in paddy-grown taro fields, where anoxic, reducing conditions may reduce sorption and release sorbed arsenic and favor the more plant-available arsenite.

, and where inorganic arsenic could be readily absorbed. (why?) The Hawai`i Department of Health performed a comprehensive study of arsenic

concentrations in plants in community gardens on soils with high total arsenic concentrations (300 to 500 mg kg-1) and found minimal elevated levels ((HDOH 2007)). It has yet to be determined whether crops and plants grown in flooded fields may have increased uptake under reduced conditions. (Seems there should be some summary paragraph or at least a few summary sentences to conclude this review of literature?)

Goals and Objectives: This report summarizes work conducted between July and September 2011 to

examine arsenic levels in aquatic plants and in soils in the Wailuku and Wailoa watersheds in Hilo, Hawai‘i. The stated objectives of the study were as follows:

(1) Conduct an assessment of total arsenic concentrations in aquatic plants that are

used as food crops in the Hilo area, especially watercress and taro. (2) Perform multiple regression analysis of total and bioaccessible arsenic

concentrations for different soil and sediment characteristics against the total arsenic concentrations in plant tissue.

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(3) Use GIS to visually present information, perform geospatial analysis where possible and identify future sites based on soil characteristics and farm locations.

Methods:

Field work and site description Four trips were made to Hilo, Hawai‘i in order to collect soil and plant samples: the

first to explore possible sites on June 17, the second to collect a preliminary set of samples on August 3, and the third as a follow-up trip to collect the final samples on September 27. On the fourth trip, on November 13, graduate student Kim Falinski worked with Ms. Pascale Pinner, high school student Erica Sampaga and middle school student Keanu Pinner to demonstrate sampling methods and protocol.

After the preliminary sampling, a two factor treatment design was developed to consider first, the presence or absence of former cane land, and second, the depth increment of the soil sampled. Using sugar cane maps from the early 1900s, two transect lines were established perpendicular to the elevation gradient in order to guide sampling. The first (called ‘AA’) ran through Kaumana Springs along the Wailuku River, and the second (‘BB’) ran through Hilo, just north of the Wailoa River (Figure 5)(Figures need to be renumbered and re-ordered. Some figures are not used and should be removed and all are out of order of use in the manuscript). A third transect was initially conceived (‘CC’) to run along the Wailoa River, but appropriate soil series were not located.

Soil collection Soil samples were collected using an auger that was cleaned with a towel between

samples, as seen Figure 21. GPS coordinates of each site were collected using a Trimble GeoXT. Two replicate samples, each one meter from the site coordinates in the opposite direction, were collected. For each replicate, three soil cores of approximately 100g each were collected approximately 30cm[kaf2] apart and composited in plastic buckets. A subsample, weighing approximately 100g, of the composite was taken and placed in a zip type bag and labeled. For the August samples, five depths were sampled: 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, and 40-50 cm. Based on the results from the August sampling, only only two or three depths (0-30 cm) were sampled in September and Novembersubsequently.

Sediment collection Sediments were collected using a 60mL sized core barrel(? Units of volume?) at Hilo

Intermediate school, in Waiakea estuary, and at the output of Waiakea estuary into Hilo Bay. Although it was originally intended to take depth profiles of the sediments, in most cases it was not possible to core to depths greater than 5 cm. Samples were stored in zip type bags. Sediment samples were dried in a soil oven at 60ºC and sieved to less than 2mm before analysis.

Sample analysis Soils were air dried for approximately one week, and then sieved onto a clean piece

of weigh paper to 2mm using a #10 sieve. After spreading the sample on the paper, a

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subsample of approximately 10g was selected to be sent to the lab for analysis. 0.5g was measured into 50mL digestion tubes. After adding 10mL of HNO3, samples were heated to 155ºC for 4 hours in a heating block. Approximately 5mL of H2O2 was then added, and the samples were heated at the same temperature for another 30 minutes. Samples were filtered using qualitative paper #42, and then analyzed using ICP-OES at the Agricultural Diagnostic Service Center (ADSC) in CTAHR at University of Hawaii at Manoa. Detection limits are approximately 20 mg/kg. Water blanks, solution standards and soil standards were included with each run to calibrate results.

Additional samples were sent to Food Quality (FQ) labs for verification of analysis of total arsenic with ICP-MS, using EPA protocol 3051a. The protocol specifies that a 0.5g sample is digested with 10mL HNO3 and HCl. Heating is done in a microwave using a fluorocarbon polymer vessel. Samples are diluted according to concentration and analyzed with ICP-MS. Several of these samples were used for quality control of the ICP-OES data. Comparison of ICP-OES results and ICP-MS results are presented in Figure 21 (Seems the figures are not numbered in order they are used in the text. Please renumber so the first used/referenced figure is figure 1 and so forth).

Plant collection and analysis Watercress samples were collected in September and November at Kaumana Springs

Lower and Carvalho Park, a site immediately about 1km downstream from Kaumana Springs. For each sample, approximately 30 subsamples of both stems and leaves were picked by hand and composited. Warabi samples were collected at Kaumana Springs Lower, Pinner Farm and Waipahoehoe sites. For warabi, only the fiddleheads were collected, as this is the part that people eat. At least 15 warabi samples were composited for each site comprising about 500g fresh weight. Samples were stored in pre-weighed paper bags after collection and while they were being dried.

In June and August, non-edible ferns were also collected, and in September clover samples were also collected. Additional samples of watercress and warabi were collected at the farmer’s market in downtown Hilo in June, August and September. Efforts were made to identify the origin of these products. The watercress sold was from a hydroponic farm, and the warabi was collected from an unknown wild location on the Hamakua coast. The non-edible ferns were collected because ferns are more likely to be hyperaccumulators, and because they may end up as forage for the cattle which use Kaumana Springs to graze.(Kim, I understand why you include this information in the report, but please be aware that this sort of ad hoc adding in of why some scientific actions were taken is not usually acceptable in scientific publications. In reports such as this you can put just about anything in the text, but in a “for publication” manuscript it would not be done. We can discuss when you develop your publication.)

Plant samples were dried within 24 hours at 65ºC in a dedicated plant oven. Dried samples were coarsely crushed with mortar and pestle and sieved to 2mm. Approximately 5g of select samples were sent to FQ Labs, with the remaining sample stored for future use. For November samples, half of the samples were immediately frozen in the event that total arsenic levels were high enough to warrant bioaccessibility testing for arsenic. Samples were analyzed for dry weight concentration using EPA Method 3051a, as outlined above. Detection limits were 0.01 mg/kg. In order to calculate the wet weight concentrations, the percent water content was determined by weighing the

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fresh samples of watercress and warabi, drying for 24 hours at 65ºC, and re-weighing immediately.

Protocol for sample collection with Erica Sampaga and Keanu Pinner On December 13, 2011, Erica Sampaga and Keanu Pinner returned to Kaumana Springs to collect additional plant, soil and sediment samples. It had been raining for several weeks, and the streams were high and the soil was saturated on the sampling day. Five decision units were defined along the banks and within the streambed of the freshwater spring. Each decision unit was approximately 30m long and one meter in width along the north bank of each watercress patch. The areas of focus for soils and sediments were the banks beside of three watercress patches, considered decision unit 1 (DU1), DU2 and DU3. DU1 and DU2 were located upstream and downstream approximately 25m apart (see Figure 3a)(out of order…) . DU3 was located further downstream, but located at near the source of a second freshwater spring. A small trowel was used to collect 30 subsamples at each site. The 30 samples were collectively taken at 5 points (with 6 samples at each point), approximately 3-4m apart, all along same side of the river bank. Approximately 50g of composited soil at each of the 5 sites at the decision unit was collected. GPS coordinates were taken using a Garmin Etrex HC. There were 3 GPS waypoints missing on return from the field, and they were approximated based on recorded waypoints. Stream sediments were collected in a similar fashion for DU1 and DU2 and were labeled DU5 and DU4, respectively. Steam sediments for DU3 could not be collected because of the river conditions on the day of sampling. Soils and sediments were split into two groups by hand[kaf3].(I recommend simply saying the samples were divided into two groups) One group was sent to University of Hawaii at Manoa, and air-dried for one month by Kim Falinski. Samples were analyzed at FQ labs, using the above described EPA 3051a protocol. A second group of samples were dried at approximately 60ºC by Erica Sampaga. The samples were then sent to the University of Hawaii at Hilo, to be analyzed by EDXRF in Dr. Steve Lundblad’s lab. Four plant samples were collected, watercress for each DU1, DU2 and DU3, and a sample of warabi taken in the same location as collected in November (in lower Kaumana Springs). Thirty subsamples of leaves and stems in each decision unit were composited to form the sample. Plant samples were collected in paper bags, and weighed within two hours in Hilo. Samples were sent by air mail to Honolulu, where they were immediately weighed again and dried at 65ºC.

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Results:

GIS A summary of the site locationss is presented in the compiled GIS maps in Figures 3a

and 3b, representing the entire Hilo area (3a) and the Kaumana Wilderness area (3b). Arsenic values presented are the maximum values at each location for all depth zones, in Figure 5. Both ICP-OES and ICP-MS analyzed samples are presented on the same map. The three transects are delineated by red lines. The GIS was completed using NAD83, Zone 5 coordinate system for all layers in a Transverse Mercator projection. The tax map key information was obtained from the Hawaii GIS repository (www.state.hi.us/dbedt/gis), and was last updated for Hawaii Ccounty in 2011. Imagery obtained from the NRCS was used to compile the soil series layers. World view® satellite imagery from 2012? 2011 was used to explore land use characteristics of the Kaumana Springs area. (Seems to me this should be included in Methods, as it is how you processed the data). The Methods so far has not mention of statistics or analysis of the data)

Soil results samples Arsenic concentrations as a function of soil depth are plotted in Figure 4.

Concentrations generally decreased with depth, although in a few cases (such as the Sheep Farm site) higher levels were found at depth compared to the surface. In lower Kaumana Springs, 82% of samples had higher concentrations at depth than[kaf4] at the surface. For the top two depth layers in sites in the general Hilo area (excluding Kaumana), coefficient of variation was 0.4, while for Kaumana Springs it was 0.51. This indicates that there was more variability in the samples taken in the Kaumana Springs area. (How can you say this. You have no test of such a statement.)

The results of the soil analysis are presented in Tables 3 and 4. Concentrations above background levels of 20 mg/kg were present at the lower Kaumana Springs sites, Naauao site and the Luana Gardens (Figure 5). At the Lehua site newly formed, highly organic Histosols(what is this! How do you know they are newly formed!) measuredbackground levels were approximately 28 mg/kg.

Plant samplesresults Plant samples, including mostly non-edible ferns, were collected at selected sites for

each sampling trip. Watercress, although previously thought to be a crop that was commonly grown in the Hilo area, was generally found to be grown hydroponically. In the Kaumana neighborhood, families grow watercress using the freshwater springs that emerge. Most of the taro grown in Hilo and on the Hamakua coast is grown in dryland conditions, although we were made aware of a family-sized wetland taro farm in Hilo after sampling had ended. In the absence of edible plantsaddition, three non-edible plant speciesferns, such as the downy woody fern (Christella dentata), were collected in order to screen for better test whether Hawaiian ferns are arsenic accumulators in lower Kaumana Springs?. Samples of the herbaceous, leguminous Desmodium tortuosum were collected based on the observation that the plant was widespread throughout the sampled

http://www.state.hi.us/dbedt/gis

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area and is available for the cattle forage. (Please use scientific writing. Too colloquial) Average values for the most important plant species are presented in Figure 6.

Edible plant samples collected on the September sampling trip were analyzed for total arsenic concentration. The results are presented in Table 1. Watercress averaged 0.56 mg/kg for all samples collected, and warabi averaged 0.045 mg/kg dry weight.. Watercress did not contain levels that would classify it a hyperaccumulator of arsenic, but it does have significantly higher concentrations than other edibles tested in East Hawaii.

Wet weight to dry weight conversions were calculated for each species. While food scientists often use fresh or wet weight concentrations for dietary calculations, it was important in this study to use dry weight concentrations to reduce differences resulting from different collection times in the field and provide a more reliable measure of As content. Watercress had an average of 22 kg of wet weight mass for every 1 kg of dry weight mass (standard deviation of 8). Watercress wilts easily, and can lose water very quickly. During sample collection, it was critical to weigh the sample immediately. For warabi, an average of 13 kg of wet weight mass for 1 kg of dry weight mass was found (standard deviation of 1).

Sediment samples Surface sediment samples were taken from the freshwater stream that runs through

Hilo Intermediate School in Hilo, HI. Samples were also taken from three points along Hilo Bay: the mouth of the Waiakea Estuary, the mouth of the Wailuku River, and at the midpoint between them (“Hilo Bay Beach”). The results are summarized in Table 54. None of the samples contained a total arsenic concentration greater than 30 mg/kg, and therefore were not further analyzed. The results from the sediment collected from the watercress patches in DU4 and DU5 is presented in Table 4.

Discussion

Possible causes of the high levels of arsenic Arsenic distribution and potential sources The data collected in this study indicate that elevated total arsenic concentrations in

soil are limited to a small area in lower Kaumana Springs (Figure 5b), although there are some sites in the general Hilo area that also have arsenic concentrations above 24 mg/kg (the HDOH action level). Of the 22 samples in the surface 0-10cm that showed elevated total arsenic levels, Kaumana Springs accounted for 20 samples. Elevated samples at Luana Gardens (up to 110 mg/kg) are likely from using “fill” soil to level the property when the house was built, as evidenced by a probable pahoehoe flow at 40cm. A single sample in lower Hilo, at Kosmic Kones, averaged 28.4 mg/kg.

There are at least two possible explanations for the spatial distribution of the data, which has very high levels of total arsenic concentrations limited to approximately an 100-m square area. The first hypothesis is that there was an undocumented arsenic herbicidal application to a small area in Kaumana Springs. Data from Erica Sampaga’s sampling indicates that while DU1 and DU2 have arsenic levels well below 24 mg/kg (1.5 mg/kg), DU3 has an extraordinarily high average (352 mg/kg). The sites are only 60m apart, and are separated by a fence. While local knowledge does not suggest that arsenical herbicides were ever used in this area, it is still possible that they were used privately. It is uncertain, though, what crop other than watercress would be grown in an

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area that is prone to flooding. Watercress is ideal for lower Kaumana Springs because the freshwater spring flows year round.

A second hypothesis considers that the arsenic is transported eroded sediment. The concentration of total arsenic with depth in lower Kaumana Springs was uneven – with high variation between within depth[kaf5] layers. Arsenic was not found at single depth horizonlayer?, indicating which would suggest that transport may have been alluvial or that the layers were disturbed by soil pugging and compaction. If compaction by ruminants wasere the reason for having high arsenic found at different depth levels throughout the Kaumana Springs area, it would be expected that the arsenic concentrations would be have less variation between sites in lower Kaumana Springsmore uniform.

There are at least two freshwater streams that flow into the Kaumana Springs Wilderness. In Figure 3b, the boundaries of the green Panaewa cobbly soil series approximate the locations of these two streams on the northern and southern boundaries, respectively. There is a discrepancy in arsenic concentrations between the north and south side (separated by only 20m) that may be significant. According to this hypothesis the sediments in the wilderness may have arrived from different origins. Originally, only the 1900 sugar cane map was available to indicate where sugar cane was grown, but newly available soil maps suggest a different story. Sugar cane would likely have been grown in Hydrudands such as the Hilo or Panaewa soil series. There is very little Hilo soil between Kaumana Springs and the south side of the Wailuku river. This is consistent with the negligible values of arsenic at the Hospital and Big Mango Tree sites, which are on the north side of Kaumana Springs.

At higher elevations to the southwest of Kaumana Springs there are Hilo and Panaewa series (see Figure 3a, the topmost part of the middle transect). Due to the fact that the freshwater springs are likely connected by lava tubes, it is possible that the freshwater flowing into Kaumana Springs originated in and carries sediment from land that was once contaminated with arsenic. Given this scenario, concentrations of arsenic would not be expected to differ so dramatically across the fence boundary in Lower Kaumana Springs. Arsenic would also be likely to be found upstream in Kaumana Spring Wilderness. Therefore it is more likely that arsenical pesticides were applied in situ

Arsenic in plants grown in flooded conditions In general, the Kaumana Springs watercress and other Kaumana Springs plant

samples contained dry weight arsenic concentrations that were approximately 10 times higher than individual garden samples collected in Kea‘au in the 2007 HDOH study that documented arsenic in leafy vegetables. Average wet weight concentrations (typically ten times lower than dry weight concentrations) in the HDOH study were less than 10 μg/kg.

It is important to consider how much arsenic is consumed on a daily basis and the body weight of the individual in order to develop an appropriate risk level. People do not typically consume as much watercress as they do rice (a well-studied crop that often is grown under flooded, reduced conditions). Watercress contains more water content than rice as well. The Hawaii DOH recommendation for arsenic levels in food is 0.3μg/kg body weight/day. For a 60-kg person, 0.018 mg/day of total arsenic would be the recommended maximum daily limit (MDL). If one assumes that 0.1 kg of watercress is

14

eaten per day, and that watercress wet weight is 22kg for 1 kg of dry weight (shown experimentally), then 0.0025 mg total arsenic would be consumed per day. This is well below the MDL.

Robinson et al (2003a) describe high concentrations of arsenic (~500 mg/kg wet weight) in watercress specimens. They note, however, that the level of arsenic in the sediments had little to no effect, but that the uptake was instead correlated to concentrations of arsenic in the water. They, in part, contradict this with laboratory studies that looked at uptake from solution with 0.4 mg/kg arsenic concentration (Robinson, 2003b). The sediment particle size was not reported in this study, a property that relates to adsorption of arsenic to the particles.

The source of arsenic in the New Zealand study was geothermal activity, leading to elevated concentrations of arsenic in the water, unlike in Hawai‘i where the source is expected to be predominantly from anthropogenic sources found in the sediment or soil. The soil used in the New Zealand experiment was Manawatu silt loam, with a pH of 4.4 and a total organic matter content of 6.3%. Further information about this soil could not be found, except that citric soluble phosphorus was considered high.

In addition, Robinson’s results (Robinson, 2003b) were based on a different species of watercress (Lepidum sativum) than isthat grown in Hawai‘i.

Researchers (see Zhao et al, 2002) have found that many species of ferns, especially of the genus Pteris, are hyperaccumulators of arsenic. Hawai’i is unique in having warabi, also known as ho’i’o, (Diplazium esculentum), as an edible fern. To our knowledge, no one has considered the health impacts of eating fiddleheads. In 2007, the HDOH conducted a soil assessment in Ke'eau, and collected a garden specimen of fern shoots that had total arsenic reported as 0.007 mg/kg. Although the region had high total arsenic levels in the soil, a soil sample was not taken at the site.

The warabi analyzed in this study contained lower total arsenic concentrations than did watercress, but also was found growing on soil with correlating arsenic concentration less than 20 mg/kg. The farmer’s market sample of warabi was of unknown origin, and therefore a correlation to soil concentration could not be established. Additional analyses of the samples collected for this study should provide a better understanding of the health risk due to eating plants grown under flooded conditions.

Conclusions Neither watercress or warabi sampled in this study contain total arsenic levels

high enough for human health risks from consumption High soil arsenic concentrations (>100 mg/kg) were mostly confined to the lower

part of Kaumana Springs Wilderness Arsenic in Kaumana Springs was likely applied on site, rather than transported

from upstream

15

Acknowledgements This work is made possible by the Hawaii Evaluation and Emergency Response Division of the Hawaii Department of Health. We would especially like to thank John Peard, Dr. Pascale Pinner and Patrick Niemeyer for their assistance.

16

Figures and Tables

0

100

200

300

400

500

600

700

0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00

ICP-OES, Total Arsenic mg/kg

ICP-

MS,

Tot

al A

rsen

ic, m

g/kg

Figure 1: Comparison of samples processed for total arsenic in both ICP-OES and ICP-MS. The black line, for reference, has a slope of 1.

Figure 2: Using an auger to collect samples.

17

Figure 3: a) Soil arsenic sampling sites in Hilo Area

18

Figure 3: b) a) Hilo, HI sites and b) Kaumana Springs Wilderness soil arsenic sampling sites, including select soil series

19

Figure 4: Depth profiles for total arsenic for various sampling locations. Colored lines represent

August sampling sites, while black lines represent September sites[GM6].

20

Figure 5a) Total arsenic data for soil samples across the Hilo area.

22

b) Figure 5 (b): Total As concentrations in Hilo (a) and Kaumana Springs Wilderness (b) study sites. Satellite imagery shows sites in relation to urban development.

23

Table 1: Plant samples analyzed for total arsenic

Plant Sample, Common Name Binomial name Sample number Location

Plant Total As Concentration

(dry weight basis) (mg/kg)

Soil Total As Concentration (mg/kg)

Watercress Nasturtium officinale 1 Kaumana Lower, South 0.557 215

Watercress Nasturtium officinale 2 Kaumana Lower, South 0.447 215

Watercress Nasturtium officinale 3 Kaumana Lower, South, DU1 0.207 1.6

Watercress Nasturtium officinale 4 Kaumana Lower, South, DU2 0.208 1.6

Watercress Nasturtium officinale 5 Kaumana Lower, South, DU3 0.37 352

Watercress Nasturtium officinale 6 Carvalho Park 0.68 -

Watercress Nasturtium officinale (sp) unknown 7 Carvalho Park 0.61 -

Watercress Nasturtium officinale 8 Waipio Valley 1.43 -

Warabi Diplazium esculentum 1 Kaumana Lower, North 0.144 11.3

Warabi Diplazium esculentum 2 Farmer’s market n/d -

Warabi Diplazium esculentum

3 Pinner Farm n/d

Warabi Diplazium esculentum

4 Chong St. Bridge n/d

Warabi Diplazium esculentum 5 Kaumana Lower, North n/d 11.3

Warabi Diplazium esculentum 6 Waipio Valley 0.13 -

24

Downy woody fern Christella dentata 1 Kaumana Lower, South 0.856 215

Florida beggarweed Desmodium tortuosum 1 Kaumana Lower, South 0.126

Table 2: Total arsenic concentrations in soils collected during the September, 2011 sampling and analyzed by ICP-MS. Depth was 0-10cm. All soils were classified as Panaewa very cobbly hydrous loam with 2 to 10 percent slopes.

Location Total As Concentration (mg/kg)

Hospital - Kaumana, West 1.62 Kaumana Springs Lower 215 Kaumana Springs Lower 29.9 Kaumana Springs Lower 11.3 Kaumana Caves * 26.8

25

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

Tota

l As

(mg/

kg)

Total As 0.440 0.034 0.856 0.126

Nasturtium officinale

Diplazium esculentum

Christella dentata

Desmodium tortuosum

Figure 6: Total As concentrations in four plant species. Error bars represent the standard error of the mean.

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Table 3: Soil samples, 0-10cm, from the September, 2011 sampling, Kaumana Springs, Island of Hawai`i.

Location Sample Number

Depth (cm) Replicate Comments

Soil Type

Transect Distance (should

use meters)

Total Arsenic

Conc (mg/kg) TA

Hospital – Sample 1 0-10 1 Panaewa 50ft Hospital – Sample 6 0-10 2 Panaewa 50ft Hospital - Northern

bank 11 0-10 Side grab Panaewa 0ft

Hospital - Northern bank 16 0-10

3 composites, every 2m length

up slope Panaewa 6ft Hospital - Northern

bank 19 0-10 Panaewa 12ft Hospital - Northern



bank 28 0-10 Panaewa 30ft Hospital - Southern

bank 31 0-10 Panaewa -6ft 1.62 Hospital - Southern

bank 33 0-10 Panaewa -24ft BigMangoTree 35 0-10 Panaewa 0ft BigMangoTree 37 0-10 Panaewa 8ft BigMangoTree 39 0-10 Panaewa 16ft BigMangoTree 41 0-10 Panaewa 24ft BigMangoTree 43 0-10 Panaewa 32ft

Hendersens 50 0-10 Transect Panaewa 0ft Hendersens 53 0-10 Transect Panaewa 8ft Hendersens 56 0-10 Transect Panaewa 16ft Hendersens 59 0-10 Transect Panaewa 24ft Hendersens 62A 0-10 Transect Panaewa 32ft Hendersens 62B 0-10 Transect Panaewa 40ft

Hendersens 70 0-10 Opp-Transect,

M2 Panaewa -6ft Hendersens 73 0-10 M3 Panaewa Hendersens 75 0-10 M1 Panaewa Hendersens 77 0-10 N1 Panaewa Hendersens 79 0-10 P1 Panaewa Hendersens 81 0-10 L1 Panaewa Hendersens 83 0-10 K1 Panaewa Hendersens 85 0-10 K2 Panaewa Hendersens 87 0-10 K3 Panaewa 215

Hendersens 89 0-10 K4 Panaewa missing sample

Hendersens 91 0-10 M4 Panaewa 29.9 Hendersens 93 0-10 N0 Panaewa 11.3 Hendersens 95 0-10 P0 Panaewa Hendersens 97 0-10 P5 Panaewa

27

Kaumana Caves 100 0-10 Hilo 26.8

Kaumana Caves 101 10-20; Hilo

Hospital - Sample 2 10-20; 1 Panaewa 50ft

Hospital - Sample 7 10-20; 2 Panaewa 50ft

Hospital - Northern bank 12

10-20; Side grab Panaewa 0ft


10-20; Panaewa 6ft


10-20; Panaewa 12ft


10-20; Panaewa 18ft


10-20; Panaewa 24ft


10-20; Panaewa 30ft

Hospital - Southern bank 32

10-20; Panaewa -6ft

Hospital - Southern bank 34

10-20; Panaewa -24ft

BigMangoTree 36 10-20; Panaewa 0ft





Hendersens 51 10-20; Transect Panaewa 0ft 39.1

Hendersens 54 10-20; Transect Panaewa 8ft



Hendersens 63A 10-20; Transect Panaewa 32ft

Hendersens 63B 10-20; Transect Panaewa 40ft

Hendersens 71 10-20;

Opp-Transect, M2 Panaewa -6ft

Hendersens 74 10-20; M3 Panaewa


Hendersens 78 10-20; N1 Panaewa

Hendersens 80 10-20; P1 Panaewa

Hendersens 82 10- L1 Panaewa DNE

28

20;

Hendersens 84 10-20; K1 Panaewa





Hendersens 94 10-20; N0 Panaewa



Pascale's House 102 10-20; Hilo

Hospital - Sample 3 20-30 1 Panaewa 50ft Hospital - Sample 8 20-30 2 Panaewa 50ft Hospital - Northern

bank 13 20-30 Side grab Panaewa 0ft Hospital - Northern





bank 30 20-30 Panaewa 30ft Hendersens 52 20-30 Transect Panaewa 0ft Hendersens 55 20-30 Transect Panaewa 8ft 97.4 Hendersens 58 20-30 Transect Panaewa 16ft Hendersens 61 20-30 Transect Panaewa 24ft Hendersens 64A 20-30 Transect Panaewa 32ft Hendersens 64B 20-30 Transect Panaewa 40ft

Hendersens 72 20-30 Opp-Transect,

M2 Panaewa -6ft Hospital - Sample 4 30-40 1 Panaewa 50ft Hospital - Sample 9 30-40 2 Panaewa 50ft Hospital - Northern

bank 14 30-40 Side grab Panaewa 0ft Hospital - Sample 5 40-50 1 Panaewa 50ft Hospital - Sample 10 40-50 2 Panaewa 50ft Hospital - Northern

bank 15 40-50 Side grab Panaewa 0ft Table 4: Soil and sediment samples from December 2012 sampling. Samples in yellow indicate values above 24 mg/kg. SampleID Decision Location Sample Total Arsenic Average

29

Unit (mg/kg) 1D 1 Upstream Bank 1 1.5 2D 1 Upstream Bank 2 1.73 3D 1 Upstream Bank 3 1.57 4D 1 Upstream Bank 4 1.44 5D 1 Upstream Bank 5 1.53 1.554 6D 2 Upper Bank 1 2.01 7D 2 Upper Bank 2 1.5 8D 2 Upper Bank 3 1.73 9D 2 Upper Bank 4 1.5 10D 2 Upper Bank 5 1.45 1.638 11D 3 Lower Bank 1 282 12D 3 Lower Bank 2 690 13D 3 Lower Bank 3 161 14D 3 Lower Bank 4 258 15D 3 Lower Bank 5 371 352.4 16D 4 Upper Sediment 1 40.5 17D 4 Upper Sediment 2 27.6 18D 4 Upper Sediment 3 17.6 19D 4 Upper Sediment 4 112 20D 4 Upper Sediment 5 29.2 45.38 21D 5 Lower Sediment 1 3.61 22D 5 Lower Sediment 2 0.52 23D 5 Lower Sediment 3 0.79 24D 5 Lower Sediment 4 0.96 25D 5 Lower Sediment 5 4.24 2.024

Table 5: Total Arsenic in Sediment Samples in the Hilo Bay Watershed

Media Type Location

Depth (cm) Replicate

Total As Conc,

Corrected (mg/kg)

Sediment Waiakea Estuary Lower

-1 0-10 1 28.7


-1 0-10 2 27.7


-2 0-10 2 26.3


-2 0-10 1 41.9


-3 0-10 1 0


-3 0-10 2 29.8 Sediment Hilo Intermediate Stream 0-10 2 10.3 Sediment Hilo Intermediate Stream 0-10 1 27.6 Sediment Hilo Intermediate Stream 0-10 3 20.2 Sediment Wailuku Mouth 0-10 25.0 Sediment Hilo Bay Beach 0-10 22.6 Sediment Hilo Bay Beach 0-10 21.8

30

References (2010). Hawaii Annual Statistics Bulletin. National Agricultural Statistics Service: 65.

Abedin, M. J., M. S. Cresser, et al. (2002). "Arsenic accumulation and metabolism in rice (Oryza sativa L.)." Environmental Science & Technology 36(5): 962-968.

Anawar, H. M., A. Garcia-Sanchez, et al. (2008). "Evaluation of various chemical extraction methods to estimate plant-available arsenic in mine soils." Chemosphere 70(8): 1459-1467.

Bacigalupo, C. and B. Hale (2011). "Soil-Plant Transfer Factors for Garden Produce from Contaminated Soils: Site Specific versus Generic Estimates for As and Pb." Human and Ecological Risk Assessment 17(2): 394-413.

Bowell, R. J. (1994). "Sorption of arsenic by iron-oxides and oxyhydroxides in soils." Applied Geochemistry 9(3): 279-286.

Bradham, K. D., K. G. Scheckel, et al. (2011). "Relative Bioavailability and Bioaccessibility and Speciation of Arsenic in Contaminated Soils." Environmental Health Perspectives 119(11): 1629-1634.

Brewer, R. (2011). Update to Soil Action Levels for Inorganic Arsenic and RecommendedSoil Management Practices, Hawaii Department of Health, HEER Office: 1-37.

Cadwalader, G. O., C. E. Renshaw, et al. (2011). "Erosion and physical transport via overland flow of arsenic and lead bound to silt-sized particles." Geomorphology 128(1-2): 85-91.

Chancho, M. J. R., J. F. L. Sanchez, et al. (2010). "Occurrence of arsenic species in the seagrass Posidonia oceanica and in the marine algae Lessonia nigrescens and Durvillaea antarctica." Journal of Applied Phycology 22(4): 465-472.

Cutler, W. (2011). Bioaccessible arsenic in the soils of the island of Hawaii. Geology and Geophysics. Honolulu, HI, University of Hawaii. PhD: 136.

El-Masri, H. A. and E. M. Kenyon (2008). "Development of a human physiologically based pharmacokinetic (PBPK) model for inorganic arsenic and its mono- and di-methylated metabolites." Journal of Pharmacokinetics and Pharmacodynamics 35(1): 31-68.

Francesconi, K., P. Visoottiviseth, et al. (2002). "Arsenic species in an arsenic hyperaccumulating fern, Pityrogramma calomelanos: a potential phytoremediator of arsenic-contaminated soils." Science of the Total Environment 284(1-3): 27-35.

Francesconi, K. A. (2010). "Arsenic species in seafood: Origin and human health implications." Pure and Applied Chemistry 82(2): 373-381.

31

Glendon-Baclig, C. (2007). Distribution and Inorganic Speciation of Arsenic in Waiākea Mill Pond and Wailoa River Estuary, Hawai‘i Island. Tropical Conservation Biology and Environmental Science. Hilo, HI, University of Hawaii at Hilo. M.S.: 113.

Ha, N. T. H., M. Sakakibara, et al. (2009). "Phytoremediation of Sb, As, Cu, and Zn from Contaminated Water by the Aquatic Macrophyte Eleocharis acicularis." Clean-Soil Air Water 37(9): 720-725.

Hallacher, L. E., E. B. Kho, et al. (1985). "Distribution of arsenic in the sediments and biota of Hilo Bay, Hawaii." Pacific Science 39(3): 266-273.

HDOH (2006). Soil action levels and categories for bioaccessible arsenic H. D. o. Health. Honolulu, HI. 06-283-RB.

HDOH (2007). Soil arsenic assessment study, Kea'au, Hawaii. H. O. Hawaii Department of Health. Honolulu, HI.

HDOH (2012). Hawaii Soil Metal Background Evaluation. Hilo, HI.

Hughes, M. F., E. M. Kenyon, et al. (2003). "Accumulation and metabolism of arsenic in mice after repeated oral administration of arsenate." Toxicology and Applied Pharmacology 191(3): 202-210.

IARC (2004). Some drinking water disinfectants and contaminants, including arsenic. W. H. Organization, International Agency for Research on Cancer. 84: 1-19.

Juhasz, A. L., J. Weber, et al. (2011). "Predicting Arsenic Relative Bioavailability in Contaminated Soils Using Meta Analysis and Relative Bioavailability-Bioaccessibility Regression Models." Environmental Science & Technology 45(24): 10676-10683.

Kurosawa, K., K. Egashira, et al. (2008). "Groundwater-soil-crop relationship with respect to arsenic contamination in farming villages of Bangladesh - A preliminary study." Environmental Pollution 156(2): 563-565.

Livesey, N. T. and P. M. Huang (1981). "Adsorption of arsenate by soils and its relation to selected chemical properties and anions." Soil Science 131(2): 88-94.

Ma, L. Q., K. M. Komar, et al. (2001). "A fern that hyperaccumulates arsenic - A hardy, versatile, fast-growing plant helps to remove arsenic from contaminated soils." Nature 409(6820): 579-579.

McDermott, S., J. L. Wu, et al. (2011). "Probability of intellectual disability is associated with soil concentrations of arsenic and lead." Chemosphere 84(1): 31-38.

32

Meharg, A. A. and M. Rahman (2003). "Arsenic contamination of Bangladesh paddy field soils: Implications for rice contribution to arsenic consumption." Environmental Science & Technology 37(2): 229-234.

Niemeyer, P. (2011). Personal communication. K. Falinski. Hilo, HI.

NTP (2011). Report on Carcinogens, Twelfth Edition. P. H. S. U.S. Department of Health and Human Services, National Toxicology Program. Research Triangle Park, NC: 50-54.

Ortiz-Escobar, M. E., N. V. Hue, and W. G. Cutler. 2006 (2006). Recent developments on arsenic: contamination and remediation. Recent Research Developments in Bioenergetics. S. G. Pandalai. 4.

Pinner, P. (2011). Personal communication. K. Falinski. Hilo, HI.

Raab, A., J. Feldmann, et al. (2004). "The nature of arsenic-phytochelatin complexes in Holcus lanatus and Pteris cretica." Plant Physiology 134(3): 1113-1122.

Rahman, M. A., H. Hasegawa, et al. (2007). "Accumulation of arsenic in tissues of rice plant (Oryza sativa L.) and its distribution in fractions of rice grain." Chemosphere 69(6): 942-948.

Rahman, M. A., H. Hasegawa, et al. (2007). "Arsenic accumulation in duckweed (Spirodela polyrhiza L.): A good option for phytoremediation." Chemosphere 69(3): 493-499.

Robinson, B., N. Kim, et al. (2006). "Arsenic hyperaccumulation by aquatic macrophytes in the Taupo Volcanic Zone, New Zealand." Environmental and Experimental Botany 58(1-3): 206-215.

Robinson, B., H. Outred, et al. (1995). "The distribution and fate of arsenic in the Waikato River System, North Island, New Zealand." Chemical Speciation and Bioavailability 7(3): 89-96.

Schoof, R. A., L. J. Yost, et al. (1999). "A market basket survey of inorganic arsenic in food." Food and Chemical Toxicology 37(8): 839-846.

Smedley, P. L. and D. G. Kinniburgh (2002). "A review of the source, behaviour and distribution of arsenic in natural waters." Applied Geochemistry 17(5): 517-568.

Wu, M. M., T. L. Kuo, et al. (1989). "Dose-response relation between arsenic concentration in well water and mortality from cancers and vascular diseases." American Journal of Epidemiology 130(6): 1123-1132.

Xu, X. Y., S. P. McGrath, et al. (2008). "Growing rice aerobically markedly decreases arsenic accumulation." Environmental Science & Technology 42(15): 5574-5579.

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Zhao, F. J., S. J. Dunham, et al. (2002). "Arsenic hyperaccumulation by different fern species." New Phytologist 156(1): 27-31.

Zhao, F. J., J. F. Ma, et al. (2009). "Arsenic uptake and metabolism in plants." New Phytologist 181(4): 777-794.

Zhao, F. J., S. P. McGrath, et al. (2010). Arsenic as a Food Chain Contaminant: Mechanisms of Plant Uptake and Metabolism and Mitigation Strategies. Annual Review of Plant Biology, Vol 61. S. Merchant, W. R. Briggs and D. Ort. Palo Alto, Annual Reviews. 61: 535-559.

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