Heavy metal and metalloid concentrations in soils under pasture of southern New Zealand

Heavy metal and metalloid (As, Cd, Cr, Cu, Hg, Ni, Pb, Zn) levels in 284 topsoil (0–30cm) samples were measured from 20,000km2 of southern New Zealand in a systematic survey and the concentrations and patterns between samples sites were studied. Samples were analysed by the inductively coupled mass spectrometry method on an aqua regia digest. Except for Hg, median concentrations from land classed as high producing exotic grassland (pasture; 241 samples) were consistently elevated relative to median natural background levels under native vegetation. The major control of heavy metal enrichment in pasture is P-based fertiliser application (Cd, Cu, Zn), the soil parent material (Ni, Hg) or a combination of both (As, Cr, Pb), with Pb also affected by proximity to urban centres and major roads. There may be a trend of increasing heavy metal concentration with increasing intensity of land use. Comparison shows there is strong, regional variation in median heavy metal concentrations in topsoil around New Zealand and highlight a need for systematic and consistent study of heavy metals in soil nationally.