Environmental risks of trace elements associated with long-term phosphate fertilizers applications: a review.

Application of phosphate fertilizer can be a significant contributor of potentially hazardous trace elements such as arsenic, cadmium, and lead in croplands. These trace elements have the potential to accumulate in soils and be transferred through the food chain. We articulated the environmental risks of trace elements associated with long-term phosphate fertilizer applications by combining data from the literature and results from model simulations. Results illustrate that under normal cropping practice, the impact of phosphate fertilizers applications on trace element accumulation in receiving soils has been limited and localized. Their plant uptake varied greatly depending on the fertilizer application rates, soil and plant characteristics. This has led to a great deal of uncertainty in characterizing soil distribution coefficients, Kd, and plant uptake factors, PUF, two of the most used parameters in assessing the risks of accumulations. Therefore, the risks may be more appropriately assessed based on the probabilistic distributions of Kd and PUF.

Uptake of metals by food plants grown on soils 10 years after biosolids application.

Potentially hazardous trace elements such as Cd, Cu, Cr, Ni and Zn are expected to accumulate in biosolids-amended soil and remain in the soil for a long period of time. In this research, uptake of metals by food plants including cabbage, carrot, lettuce and tomato grown on soils 10 years after biosolids application was studied. All the five metals were significantly accumulated in the biosolids-amended soils. The accumulation of metal in soil did not result in significant increase in concentrations of Cu, Cr and Ni in the edible plant tissues. However, the Cd and Zn concentrations of the edible tissues of plants harvested from the biosolids receiving soils were significantly enhanced in comparison with those of the unaffected soils. The plant uptake under Greenfield sandy loam soil was generally higher than those under the Domino clayey loam soil. The metal concentration of edible plant tissue exhibited increasing trends with respect to the concentrations of the ambulated metals. The extents of the increases were plant species dependent. The indigenous soil metals were absorbed by the plants in much higher rates than those of the biosolids-receiving soils. It appeared that the plant uptake of the indigenous soil-borne metal and the added biosolids-borne metals are independent of one another and mathematically are additive.

A root exudates based approach to assess the long-term phytoavailability of metals in biosolids-amended soils.

Organic acids present in the rhizosphere of growing plants are widely recognized to be responsible for dissolving the solid phase metals in the soil and making them available for plant absorption. We proposed a root exudates-based model to assess the long-term phytoavailability of metals in biosolids-amended soils. The phytoavailability of biosolids-borne metals was defined in terms of a capacity factor and an intensity factor. The plant available metal pool, C(0) (capacity factor, mgkg(-1)), can be estimated by fitting the successive organic acids extraction data to an exponential decay kinetic equation. The field metal removal rate, k (intensity factor, yr(-1)), can be estimated from the successive extraction-based metal release rate through an effective annual organic acid production in the rhizosphere which was found to be characteristic of plant species. The protocol was successfully used to assess the long-term phytoavailability of metals in biosolids-amended soil from two biosolids land application sites.

[Modeling transfer and partitioning of potentially toxic pollutants in soil-crop system for human food security].

Human exposure to potential toxic pollutants and the associated health risk is a focus of current environmental and medical studies. However, the transfer and partitioning of the pollutants in the soil-crop systems turns to be a key problem for evaluating the food intake of the pollutants. This paper deals with the methodology and the approach of computer modeling of the soil-crop partitioning of the pollutants under agricultural systems for human food security and the elaboration of guidelines for soil protection. Two major models, crop ecological model and soil environmental chemical model, are discussed respectively. These models may be valuable for the research of agricultural environment protection and the development of guidelines for soil protection in China.