POP accumulation in the food chain: Integrated risk model for sewage sludge application in agricultural soils

Because of its benefits to soil and crops, sewage sludge application on agricultural soils is a managing practice of increasing use. However, this practice may lead to contamination of the food chain, especially by persistent organic pollutants (POPs). The main objective of this study was to integrate probabilistic multimedia models to predict the accumulation of POPs in the food chain and the related risks to humans, as a consequence of sludge application on soil. For that, four models were integrated: (i) soil fate, (ii) plant, (iii) food chain and (iv) exposure and risk. These models were applied for two scenarios (occupational and non-occupationally exposed populations) in a time span of 30 years. The variability of the inputs and outputs was also considered. The model was applied to a case-study of 4 POPs (2,3,7,8TCDD, PCB 180, benzo(a)pyrene, and dibenzo(a,h)anthracene) in an agricultural soil located in Catalonia (NE of Spain). Some differences in cancer risk due to POP exposure were appreciated between both evaluated scenarios. However, all values were below the threshold levels. With the exception of 2,3,7,8TCDD, all the contaminants reached steady state on soil in the first five years of the evaluation. Concentration levels in food (vegetables, meat and milk) were linearly correlated to those in soils. Air inhalation was noted to be an occupational exposure route of minor importance. Sensitivity analysis for 2,3,7,8TCDD showed that exposure parameters were responsible for most of the variability in the results.