Metals and micronutrients - food safety issues

Of all the elements, the most important to consider in terms of food-chain contamination are arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb) and s elenium (Se). Where soils are enriched in these elements, it is usually thr ough the agricultural, industrial or urban activities of man, except for Se where high concentrations in soil are often derived from high-Se parent ro ck materials. The propensity for plants to accumulate and translocate these contaminants to edible and harvested parts depends largely on soil and cli matic factors, plant genotype and agronomic management, Elevated As intake, especially of inorganic As, is most likely to arise from high-as drinking water than from ingestion of food. Cadmium and Se are of the greatest conce rn in terms of terrestrial food-chain contamination, with the former elemen t receiving most attention. Worldwide, the probability of insufficient Se i n the human diet exceeds that of toxicity, with deficiency usually associat ed with monotonous vegetarian diets in areas with Se-deficient soils. Exces sive human intake of Cd is of concern as this element accumulates over a li fetime in the body, with impairment of kidney function being the main adver se effect. Cadmium inputs to soil in fertilizer, biosolids, soil amendments and atmospheric deposition often exceed outputs in crops and drainage wate rs, so that Cd concentrations in many agricultural soils are slowly increas ing. However, evidence for increases in Cd concentrations in crops over tim e is contentious, as is the evidence for human health problems due to low-l evel Cd contamination of the food chain. Adverse health effects due to Cd i ntake have been manifest only in situations of gross soil contamination, wi th a predominantly rice-based diet, where soil-plant and plant-human transf er of Cd would have been enhanced. Human feeding studies have indicated tha t food Cd bioavailability is dependent on Fe nutrition, and animal studies have indicated that Zn, Ca, P and other elements and food constituents (e.g . fiber, phytate) affect Cd bioavailability. While plant breeding and agron omic management can minimize soil-plant transfer of Cd, and maximize concen trations of antagonists to Cd assimilation in humans, it remains important that inputs of this metal to soil be minimized. (C) 1999 Elsevier Science B .V. All rights reserved.