FOOD SAFETY ISSUES FOR MINERAL AND ORGANIC FERTILIZERS

Fertilizers and other soil amendments are required to maintain soil fertility, but some may be naturally rich in trace elements, or contaminated. As part of the overall consideration of using fertilizers and soil amendments, one should consider the levels of trace elements present in relation to soil, plant, and food-chain processes (precipitation, adsorption, chelation) which promote or alleviate trace element risks. These natural processes limit plant accumulation of nearly all elements to levels which would not cause harm to humans, livestock, wildlife, or soil organisms. Soils geologically rich or contaminated with Mo can harm ruminants, while those rich in Se may harm all plant consumers; Mo or Se should be applied only when needed. Manures from swine and poultry may be rich in Cu, Zn and/or As from feed additives. Crops except rice accumulate little As from soils, so soil ingestion is the basis for soil As risk except for rice. Pb risk is also through soil ingestion rather than plant uptake. Cd is accumulated by rice to levels which caused human disease (renal tubular dysfunction) where rice soils were contaminated by industrial discharges. Risk from Cd in rice is strongly affected by the high bioavailability of rice Cd. Consumption of similar amounts of Cd have not caused harm from other foods. Because phosphate fertilizers may contain high levels of Cd, and use of high Cd superphosphate in Australia caused significant increase in wheat and potato Cd levels, risk from long-term accumulation of phosphate fertilizer Cd (and other sources) must be controlled. Different control schemes are discussed.