REVIEW - THE BEHAVIOR AND ENVIRONMENTAL-IMPACT OF CONTAMINANTS IN FERTILIZERS

The risks of contaminants accumulating in soils and crops due to inadv ertent addition of impurities in agricultural fertilizers and soil ame ndments were assessed for Australian conditions. Elements considered o f concern were arsenic (As), cadmium (Cd), fluorine (F), lead (Pb) and mercury (Hg). Consideration of background concentrations of these ele ments in Australian soils, inputs to soil in fertilizers and offtake i n harvested crops indicates that Cd and F will accumulate in fertilize d soils at a faster rate than As, Pb or Hg. The major factors affectin g the accumulation of fertilizer-derived Cd, F, Hg and Pb in soils and their transfer to agricultural crops are reviewed in an Australian co ntext where data are available. Cadmium is the element of most concern as its transfer from soils to the edible portions of agricultural foo d crops is significantly greater than for other elements. After consid eration of the behaviour of F, Hg and Pb in the soil-plant system, we conclude that these elements pose negligible risk of accumulating to t oxic concentrations in agricultural food crops. Proposed regulations g overning maximum permitted concentrations (MPCs) of F in soils may nee d review and critical concentrations of F in agricultural soils need d efinition, given current F loadings to soil from fertilizers. Some agr icultural produce currently exceeds Australian MPCs for Cd. However, t he levels observed in crops and soils are in a range similar to those found internationally. While Cd concentrations in Australian phosphati c fertilizers have been historically high in comparison with fertilize rs used in other countries, lower inputs of fertilizer per unit area a nd less atmospheric contamination of soils have resulted in similar or lower Cd loadings to agricultural land compared with Europe. In recen t years the use of phosphatic fertilizers with lower Cd concentrations and the development of plant cultivars which restrict Cd uptake shoul d assist in control of Cd accumulation by crops. However, acidificatio n and salinization of soils in Australia poses a threat in terms of in creasing Cd concentrations in agricultural produce. In comparison with other trace metals, Cd availability to plants appears to decline only slowly with time, if at all. More Cd is currently added to Australian soils than is removed in agricultural produce or by leaching. It is t herefore important that the long-term behaviour of Cd in Australian so ils be assessed, to determine if Cd concentrations in agricultural pro duce will slowly increase over time.