Bioaccumulation of organochlorines in freshwater fish with different feeding modes cultured in treated wastewater

Five species of freshwater fish including black bass (Micropterus salmoides), tilapia (Oreochromis mossambicus), big head (Aristichthys nobilis), silver carp (Hypophthalmichthys molitrix) and grass carp (Ctenopharyngodon idellus) cultured in a wastewater system were used to study the bioaccumulation of DDTs, HCHs and PCBs. The wastewater system comprised of eight ponds. After sedimentation (ponds S1–S2) and aeration (ponds A1–A2), the treated wastewater was used for fish culture (ponds C1–C4). p, p′-DDT and HCHs were undetectable in all the samples. When comparing the levels of DDTs and PCBs in the sediments of the inlet (S1) and outlet (C4) of the system, about 58% of DDTs and 85% of PCBs were removed (based on the concentration of DDTs and PCBs in S1 as 100%) after sedimentation and aeration. Black bass contained the highest (p<0.05) levels (lipid based) of both DDTs (0.76 μg/g) and PCBs (3.4 μg/g), followed by tilapia (DDTs: 0.090 μg/g and PCBs: 3.1 μg/g), grass carp (DDTs: 0.087 μg/g and PCBs: 2.1 μg/g), silver carp (DDTs: 0.038 μg/g and PCBs: 1.6 μg/g) and big head (DDTs: 0.040 μg/g and PCBs: 0.87 μg/g). The homologue pattern of PCBs varied between fish species. There were marked differences in average chlorine numbers between fish species with different feeding habits, and the average chlorine numbers observed in fish muscle were 3.5 for grass carp, 4.5 for big head, 4.8 for silver carp, 5.0 for black bass and 5.2 for tilapia. These results indicated that feeding habits intervened in the PCBs accumulation process. Higher contents of PCBs and chlorine number were found in black bass which located in the highest trophic level.