Occurrence and levels of persistent organic pollutants (POPs) in wild and farmed tilapia (Oreochromis niloticus) from Lake Kariba, Zambia: possible impact on fish health

The current study was carried out to determine occurrence and levels of persistent organic pollutants (POPs) in wild and farmed tilapia (Oreochromis niloticus) in Lake Kariba, Zambia, and possible implications for fish health. Concentrations of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyls (PBDEs), hexabromocyclododecane (HBCDD) and perfluoroalkyl substances (PFASs) were determined in liver samples of tilapia. Concentrations of POPs in wild tilapia were in general higher than in farmed tilapia, however, concentrations of DDTs and PCBs in wild tilapia foraging near the fish farms were more in the range of the farmed fish. The highest median ∑DDTs (93 and 81 ng/g lw) were found in wild tilapia from sites 1 and 2, respectively 165 km and 100 km west of the farms. DDE/DDT ratios seem to indicate recent exposure to DDT. The highest median of ∑ 17 PCBs (3.2 ng/g lw) and ∑ 10 PBDEs (8.1 ng/g lw) were found in wild tilapia from site 1 and 2, respectively. The dominating PCB congeners were PCB-118, -138, -153 and -180 and for PBDEs, BDE-47, -154, and -209. Of PFASs, only PFOS, PFDA and PFNA were detected in wild fish with highest median PFOS levels in site 1 (0.66 ng/g ww). The PCB and BDE concentrations in wild and farmed fish were above EQS biota limits set by the EU. This may suggest a risk to the fish species and threaten biodiversity.