Abstract/Summary

Recycled bioresources (biosolids, compost-like-output, meat and bonemeal ash, poultry litter ash, paper sludge ash) were added to the feed of dairy cattle to simulate incidental ingestion from agricultural utilisation, to investigate the transfer of organic contaminants from the ingested materials to milk. The bioresources were blended with a loamy sand soil at agronomic rates to simulate a single application to land, which was added to the diet at 5% of the total intake on a dry matter (DM) basis. Biosolids, and control treatments consisting of unamended soil, were also added directly to the feed at 5% DM. The cattle were fed the bioresource amended diets for a target period of three to four weeks, depending on material, and monitoring continued for four weeks after treatment withdrawal. Milk samples were taken weekly with chemical analysis of selected samples for a range of organic contaminants including: polychlorinated, polybrominated and mixed-halogenated dioxins, furans and biphenyls, polychlorinated naphthalenes and alkanes (often called chlorinated paraffins), polycyclic aromatic hydrocarbons and chlorobenzenes. No statistically significant additional transfer of organic contaminants to the milk was detected when bioresources were blended with soil due to the relatively low levels of contaminants present when the bioresources were blended with soil at agronomic rates. However, direct biosolids ingestion by cattle significantly increased the transfer of contaminants to milk in comparison to control animals. Although present in larger concentrations in biosolids than their chlorinated counterparts, the carry over rates and bioconcentration factors for brominated dioxins and furans were considerably smaller. Direct ingestion of biosolids resulted in most contaminants approaching, but not always completely reaching, steady state concentrations within the treatment feeding period, however, concentrations generally declined to control values within four-weeks after withdrawing the biosolids-amended diet.