Ingestion of sludge applied organic chemicals by animals.

Intake of sludge-borne chemicals is related to the crop and animal management systems, the species and physiological status of animals, and the properties of the chemicals. The greatest intake occurs when sludge is applied to established crops and animals have immediate access. Intake is reduced when access is delayed to allow losses by weathering and dilution by plant growth, or when sludge is incorporated into soil because vapour transport from soil to plants and lower concentrations at the surface reduce intake via soil ingestion. Animals that consume forage are the most subject to contaminant exposure, which is maximized when pasture is the major component of the diet because soil ingestion is an additional exposure pathway. Of the many organic contaminants in sludges, only lipophilic halogenated hydrocarbons accumulate in animal tissues and products. Compounds like phthalate esters, PAHs, acid phenolics, nitrosamines, volatile aromatics, and aromatic surfactants are metabolized and do not accumulate. Among halogenated hydrocarbons, compounds with low degrees of halogenation are metabolized and do not accumulate, but higher degrees of halogenation block metabolism, and concentrations in milk and tissue fat may be several-fold greater than in the diets.