A multi-medium chain modeling approach to estimate the cumulative effects of cadmium pollution on human health.

Cadmium is a highly persistent and toxic heavy metal that poses severe health risks to humans. Diet is the primary source of human exposure to cadmium, especially in China. Soil, as the main medium that transfers cadmium to rice, can be used as a helpful indicator to predict human exposure to cadmium in soils. There is, however, very little work that links a soil-rice transfer model with a biokinetic model to assess health risks. In this work, we introduce a multi-medium chain model based upon a soil-rice-human continuum to address this issue. The model consists of three basic steps: (i) development and validation of a soil-rice transfer model for cadmium based on 189 pairs of measured data in Wenling of Zhejiang province in Southeast China; (ii) calculation of weekly exposure based on the nationwide monitoring and survey results; (iii) linking the exposure model with a modified biokinetic model proposed with a classic biokinetic model to predict urinary cadmium, which is a biomarker to assess the health risks. Results indicated that the developed soil-rice-human transfer model predicted well the urinary cadmium levels in humans subjected to age and exposure uncertainties. We observed a maximum of 0.71 µg g-1 creatinine in males and 1.53 µg g-1 creatinine in females at 70 years old under median cadmium exposure, which was consistent with previous studies. Sensitive analysis was also conducted to detect the sensitive parameters that have the most significant influences on the output of the model. The new risk assessment strategy proposed in this work is beneficial for predicting the cumulative cadmium levels in various exposed populations so that we can quickly identify the critical areas from basic soil properties.

Contrasting effects of alkaline amendments on the bioavailability and uptake of Cd in rice plants in a Cd-contaminated acid paddy soil.

Reducing cadmium (Cd) concentrations in rice grains is important for food safety, particularly in acid paddy fields in South China where the soils have been previously contaminated with Cd. A field experiment was conducted to evaluate the effects of four alkaline amendments, i.e., lime, compost, biochar, and carbide slag on soil bioavailability and uptake of Cd in plants of two rice cultivars (Oryza sativa L.) in a Cd-contaminated acid paddy soil. The addition of these amendments significantly decreased the concentrations of CaCl2-extractable Cd by 13-41%. Cd in the acid-soluble fraction was decreased in these amended soils while it increased in the residual fraction. The amendments also decreased the uptake of Cd in the plants at the tillering and mature growth stages. The concentrations of Cd in plant tissues at maturity were in the order: root > shoot > bran > polished rice > husk. The amendment of carbide slag decreased Cd concentration in rice grains the most, followed by lime, biochar, and compost. The increases in soil pH and the decreases in the acid-soluble fraction of Cd (F1-Cd) indicated that these amendments can directly transform the highly availability fraction of Cd to a more stable fraction (residual Cd fraction) in soils. Furthermore, the Cd concentrations in polished rice grains of the two rice cultivars used were reduced by 66-67% by treatment with carbide slag. Our study suggests that carbide slag has a great potential to reduce the bioavailability and uptake of Cd in rice plants in Cd-contaminated acid paddy field soils.

Contrasting effects of composting and pyrolysis on bioavailability and speciation of Cu and Zn in pig manure.

The intensive and unregulated application of feed additives to commercial pig foods has resulted in high levels of Cu and Zn in pig manure. The aim of this study was to assess the impacts of composting and pyrolysis processes on the bioavailability and chemical speciation of Cu and Zn in pig manure products by single and sequential extractions, and to compare metal bioavailability in composts and biochar-amended soils in incubation experiments. Composting and pyrolysis processes can convert exchangeable and carbonate-bound Cu and Zn to organic matter and residual fractions, and significantly reduce the potential availability of metals in composts and biochars. The DTPA-Cu and Zn concentrations in soils amended with biochar BC700 were lower than in composts and soils amended with biochar BC400. It is suggested that 700 °C is the preferred pyrolysis temperature for the conversion of pig manure contaminated with heavy metals to biochar, in order to minimize environmental pollution.