Prediction of Dispersion and Bioaccumulation of Chlorinated Benzene Pollutants in a River Section for a Low Level of Discharge

Abstract

(Poly)chlorinated benzenes (CBz) are a category of persistent organic pollutants (POP) difficult to be removed from wastewaters and environment. CBz with five and six chlorine-atoms in the molecule present a very low biodegradability and high toxicity comparable to PCBs (polychlorinated biphenyls), making their removal incomplete in conventional (chemical-biological) wastewater treatment plants (WWTP), and frequent oversteps of the admissible limits in effluents (0.4-3.2 ng/L) are reported worldwide. However, accidental discharges of low loads may turn into a serious pollution problem, even for small POP concentrations in the WWTP effluent, due to their high bioaccumulation capacity in the aquatic environment (biota, sediments). The paper illustrates, by means of a comparative study including eleven CBz, the high pollution potential for the river caused by a low-level but frequent CBz discharge. By using a combined advective-dispersive dynamic model, including the phase-exchange, bioaccumulation in biota and sediments, and the pollutant biodegradation and evaporation, simulations point-out how a CBz release can become dangerous on a long term, by predicting the �moving pollution front� effect propagated downstream the river as soon as the aquatic phase-exchange equilibrium tends to be reached in the critical discharge section.