NATURAL BACKGROUND TOPSOIL ARSENIC CONCENTRATIONS

AND SOME IMPLICATIONS FOR APPLYING SGVs(HEALTH)

Daniel Moore Mathew Taylor

Ministry for the Environment Environment Waikato

Introduction

• Acknowledgements

• Policy : toxicological vs. natural

• Limited published arsenic data

• Regional council data request

Timber Treatment Guidelines 1997

“The nominated criterion should not be less than a reasonable background concentration of arsenic. In this regard a value of, say, 30 mg/kg may be appropriate (Spier, 1997) notes that typically background concentrations of arsenic in New Zealand soils range from 2 to 30 mg/kg)”

Arsenic dataset

• Collate existing data

• Sample density, variability, confidence

• Identification of data limitations

• Assess key drivers of landscape-scale

variation

Regional data summary Region Total Number of

SamplesNumber of Background

SamplesSampling Depth

(cm)No of cores per sample

Auckland 96 96 0-15 4

CD Auckland 40 0 0-7.5 10

CD Tasman 25 0 0-7.5 10

Marlborough 14 0 0-7.5 25

Marlborough 46 6 0-10 15

CD Waikato 44 7 0-7.5 10

Waikato 267 32 0-10 4

Hawke’s Bay 22 22 0-10 ?

Hawke’s Bay 4 4 0-15 ?

Wellington 110 25 0-10 20

URS Wellington 59 55 0-15 4

Canterbury 90 73 0-15 4

Bay of Plenty 98 17 0-10 50

NZ wide Longhurst et. al., (2004) 398 86 0-2.5 and 2.5-7.5 16

Data analysis

• Data quality

• Standardised land use

• Standardised soil type

• Data desk

• Pooled t-test

Data limitations

• Variation in the sampling and

analysis methodology

• Poor land use classification

• Representative Background data

• Variation due to soil type

• The effect of soil bulk density

Conclusions

• Bush, indigenous forest, native = background

• National As average 6.0 mg/kg

• Background As average 4.5 mg/kg

• Cropping, horticulture and urban land uses higher

concentrations than background.

• Waikato region statistical significance

Upcoming

• Cadmium

• Publish SGV comparisons

• Data email: daniel.moore@mfe.govt.nz

• Questions?