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 selenium (Se). Where soils are enriched in these elements, it is usually through the agricultural, industrial or urban activities of man, except for Se where high concentrations in soil are often derived from high-Se parent rock materials. The propensity for plants to accumulate and translocate these contaminants to edible and harvested parts depends largely on soil and climatic 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 concern in terms of terrestrial food-chain contamination, with the former element receiving most attention. Worldwide, the probability of insufficient Se in the human diet exceeds that of toxicity, with deficiency usually associated with monotonous vegetarian diets in areas with Se-deficient soils. Excessive human intake of Cd is of concern as this element accumulates over a lifetime in the body, with impairment of kidney function being the main adverse effect. Cadmium inputs to soil in fertilizer, biosolids, soil amendments and atmospheric deposition often exceed outputs in crops and drainage waters, so that Cd concentrations in many agricultural soils are slowly increasing. However, evidence for increases in Cd concentrations in crops over time is contentious, as is the evidence for human health problems due to low-level Cd contamination of the food chain. Adverse health effects due to Cd intake have been manifest only in situations of gross soil contamination, with a predominantly rice-based diet, where soil-plant and plant-human transfer of Cd would have been enhanced. Human feeding studies have indicated that 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 agronomic management can minimize soil-plant transfer of Cd, and maximize concentrations 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.