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Location: Adaptive Cropping Systems Laboratory

Title: Food Safety Issues: Mineral fertilizers and soil amendments

item Chaney, Rufus

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 4/15/2012
Publication Date: 8/25/2012
Citation: Chaney, R.L. 2012. Food Safety Issues: Mineral fertilizers and soil amendments. In: Sparks, D.L., editor. Advances in Agronomy. New York, NY: Elsevier Press. p. 41-106.

Interpretive Summary: Fertilizers and other soil amendments are required for optimal crop production, and are usually applied at rates needed to supply required nutrient for plant growth. All soil amendments contain trace elements at some concentration, but some contain higher levels which may require regulatory control or management to prevent adverse effects of the trace elements. This chapter is a comprehensive review of the occurrence and potential adverse effects of trace elements in soils and soil amendments. Some soils are rich in specific trace elements from the geological parent materials. Mo and Se toxicity to livestock are well known effects from mineralized soils at specific locations. Both elements are readily accumulated by plants without causing phytotoxicity. Excessive Mo can harm ruminants by inducing Cu deficiency. Se is a potential risk to both ruminants and monogastric animals, and even humans have been harmed by excessive Se in coal ash applied on fields in China. Manures may contain high levels of Cu, Zn and As from feed supplements. Only Zn is likely to cause phytotoxicity with food-chain risks and then only in very strongly acidic soils after many decades of application at fertilizer rates. Cu has not shown evidence of causing phytotoxicity or other risks from applied manures, but specific Cu uses on farms should be avoided to protect manure quality. As is of most concern for rice cropland because the flooding causes soil microbes to generate arsenite which is more soluble than arsenate, and some arsenite is accumulated by rice and translocated to grain. Other crops have very low translocation of soil As to edible plant tissues. Concern about dietary As is complex and controversial, and even the application of As to rice soils causes little increase in grain As until toxicity is reached. Cadmium is given wide consideration because Cd is present in all phosphate fertilizers and all manure, and may be present in other soil amendments depending on their source. Rice transfers more soil Cd into grain than other crops, and the bioavailability of rice Cd is high compared to other foods. Cd issues are discussed in depth. Present regulations of Cd in phosphate fertilizers is likely extreme in some jurisdictions and inadequate in some others. The high Cd: Zn ratio of Cd in phosphates causes more risk than Cd in most other soil amendments including manure and biosolids. Fluoride occurs at 1-3% in most phosphate fertilizers, and the main concern is ingestion of product by livestock. After reaction of the fertilizer fluoride with soil, bioavailability is low, and the level of ingestion is low enough to prevent risk. High fluoride in any soil amendment may be a concern so analysis is needed. The chapter closes with discussion of an episode of deliberate Cd contamination of a Zn-fertilizer product by an exporter. Although US regulation at the State level protected US growers from this product being sold in the US, highly Cd-contaminated Zn fertilizer was sold in other countries where it caused food Cd to reach levels which prevented sale. This case indicates that most countries do not have sufficient regulation or enforcement capability to prevent such unacceptable materials from being sold to growers, and show the need for improvement. Although specific cases illustrate the hazards of trace elements in soil amendments, few adverse effects occur because the knowledge is available to regulators and farm managers.

Technical Abstract: Fertilizers and other soil amendments are required to maintain soil fertility, but some may be naturally rich in trace elements, or contaminated. Thus, 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 which promote or alleviate trace element risks. These natural processes prevent plant accumulation of nearly all elements to levels which would 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 or As from feed additives. Extreme concern about As in rice grain appears not to be supported by the evidence, but will remain controversial until the basis for risk is clarified. 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 regulated. Different regulatory schemes are discussed.