Developing site-specific guidelines for orchard soils based on bioaccessibility – Can it be done?

Abstract

Horticultural land within the periurban fringe of NZ towns and cities increasingly is being developed for residential subdivision. Recent surveys have shown that concentrations of As, Cd, Cu, Pb, and ΣDDT (sum of DDT and its degradation products DDE and DDD) in such soils can exceed criteria protective of human health.¹ Soil ingestion is a key exposure pathway for non-volatile contaminants in soil. Currently in NZ, site-specific risk assessments and the derivation of soil guidelines protective of human health assume that all of the contaminant present in the soil is available for uptake and absorption by the human gastrointestinal tract. This assumption can overestimate health risks and has implications for the remediation of contaminated sites.² In comparison, the bioavailability of contaminants is considered when estimating exposure via dermal absorption and by ingestion of home-grown produce.³ Dermal absorption factors and plant uptake factors are included in the calculations for estimating exposures via these routes.