Improving prediction of metal uptake by Chinese cabbage (Brassica pekinensis L.) based on a soil-plant stepwise analysis.

It is crucial to develop predictive soil-plant transfer (SPT) models to derive the threshold values of toxic metals in contaminated arable soils. The present study was designed to examine the heavy metal uptake pattern and to improve the prediction of metal uptake by Chinese cabbage grown in agricultural soils with multiple contamination by Cd, Cu, Ni, Pb, and Zn. Pot experiments were performed with 25 historically contaminated soils to determine metal accumulation in different parts of Chinese cabbage. Different soil bioavailable metal fractions were determined using different extractants (0.43M HNO3, 0.01M CaCl2, 0.005M DTPA, and 0.01M LWMOAs), soil moisture samplers, and diffusive gradients in thin films (DGT), and the fractions were compared with shoot metal uptake using both direct and stepwise multiple regression analysis. The stepwise approach significantly improved the prediction of metal uptake by cabbage over the direct approach. Strongly pH dependent or nonlinear relationships were found for the adsorption of root surfaces and in root-shoot uptake processes. Metals were linearly translocated from the root surface to the root. Therefore, the nonlinearity of uptake pattern is an important explanation for the inadequacy of the direct approach in some cases. The stepwise approach offers an alternative and robust method to study the pattern of metal uptake by Chinese cabbage (Brassica pekinensis L.).

Risk assessment of manufacturing equipment surfaces contaminated with DDTs and dicofol.

Decommissioning of manufacturing plant in the chemical industry includes inspection of the surfaces of production equipment for potential contamination and associated health risks. In the present study wipe-samples were taken from the surfaces of dicofol manufacturing equipment at a chemical factory in north China and analyzed for chemicals of concern (COCs). Occupational hygiene assessment was conducted to assess the risks to demolition workers and health risk assessment was performed to evaluate the risks to demolition and general industrial workers. The concentrations of COCs on the equipment surfaces were found to be 0.54-3.75 × 10(4)mg DDTs m(-2) and 0.15-4.38 × 10(3)mg dicofolm(-2). The average concentration of p,p'-DDT does not represent an unacceptable risk to the demolition workers using occupational hygiene assessment. Under the industrial scenario the carcinogenic risks of COCs ranged from 2.28 × 10(-7) to 1.79 × 10(-2) for p,p'-DDT, 6.18 × 10(-7) to 3.04 × 10(-3) for p,p'-DDD and 1.89 × 10(-6) to 0.16 for p,p'-DDE. The non-carcinogenic hazard indices ranged from 3.86 × 10(-3) to 3.03 × 10(2) for p,p'-DDT and 1.16 × 10(-3) to 33.94 for dicofol. Both carcinogenic risk and hazard index of COCs under the industrial scenario were higher than under the demolition scenario. Oral ingestion and dermal contact were the major pathways and accounted for >88% of the total exposure of COCs. Parameter sensitivity analysis shows that equipment surface concentration (Cs), frequency of contact with surface (EV), fraction of dust transferred from surface to skin (FTss) and exposure frequency (EF) were the most sensitive parameters and these should be acquired on a site-specific basis. The accuracy of the risk assessment was controlled largely by the variation in the sensitive parameters and the uncertainty of the exposure model for the inhalation pathway.