Persistent Organochlorine Compounds Levels in Selected Fish Species from Lake Victoria and Associated Human Health Risks

Abstract

Nile perch (L. niloticus) and Nile tilapia (O. niloticus) are the major commercial fish species in Lake Victoria region of Tanzania. This study was conducted to assess the levels of persistent organochlorine compounds, namely PCBs and OCPs in these two fish species and the probable human health risks associated with the consumption of these two fish species from Lake Victoria. Fish samples were collected between May and August 2016 and the necessary anthropometric measurements such as length and weight were taken. The extraction was done using a modified QuEChERS method and the identification and quantification of the chemicals were done using GC/ECDs. The results of this study revealed that fish species sampled were undersize, which was an indication of overfishing and abuse of bylaws. Among the 19 OCPs which were considered, only four (β-HCH, HCB, Aldrin and Dieldrin) were detected at measurable quantities. β-HCH ranged from <0.24 to 1.19µg/kg. The mean concentrations were 0.77±0.43µg/kg and 0.56±0.16µg/kg for L. niloticus and O. niloticus respectively. HCB levels ranged from <0.18 to 0.59µg/kg in L. niloticus and <0.18µg/kg in O. niloticus. Aldrin ranged from <0.14 to 0.34µg/kg in L. niloticus whereas it was not detected in O. niloticus. Moreover, Dieldrin residues ranged from <0.17 to 1.06µg/kg in O. niloticus but were not detected in L. niloticus. Generally, there were slightly higher levels of the detected OCPs in L. niloticus than the corresponding levels in O. niloticus mainly due to their differences in trophic levels and feeding habits. The indicator PCBs were not detected in all the investigated fish samples. The levels of all the detected organochlorines were far below the MRL set for fish and fishery products suggesting that the fresh fish from Lake Victoria are safe for human consumption. Low levels of the detected residues and non-detection of many organochlorines considered indicate that contamination in Lake Victoria has not reached alarming levels. The human health risk assessment of the detected organochlorines showed cancer risk from 8.6E-06 to 3.2E-05 for children and from 7.8E-06 to 1.3E-05 for adults indicating that there is a low cancer risk for both age groups. The non-cancer risks (HI) on the other hand, were 5.7E-02 for children and 4.7E-02 for adults, which is an indication of an insignificant risk.

Assessment of health risks associated with organochlorine pesticides levels in processed fish products from Lake Victoria

“…The concentrations of Lindane in all fish products were below the maximum residual limit (MRL) of 100 µg/kg set for fishery products (Biogo et al, 2010). The levels of HCHs determined in this study were far higher than those that were determined by Wenaty et al (2019) in fresh species of L. niloticus and O. niloticus from the same study area. In a study by Wenaty et al (2019), the levels of α-HCH and γ-HCH were below their lowest limits of detection (LODs) in both fish species while the concentration of β-HCH was up to 1.19 µg/kg in L. niloticus and 0.60 µg/kg in O. niloticus.…”

“…Thirty grams of each sample were measured in triplicates and homogenized using a blender. Fifteen grams of the homogenized samples were transferred into 100 mL centrifuge tubes as described by Wenaty et al (2019). Thereafter, 2.5 g of sodium bicarbonate (NaHCO3), 60 mL of ethyl acetate and 15 g of anhydrous Na2SO4 were added and placed in a shaking machine to homogenize for 20 min.…”

“…Thereafter, 2.5 g of sodium bicarbonate (NaHCO3), 60 mL of ethyl acetate and 15 g of anhydrous Na2SO4 were added and placed in a shaking machine to homogenize for 20 min. The supernatants were transferred into 15 mL centrifuge tubes containing 0.125 g of primary secondary amine (PSA) and 0.75 g of anhydrous MgSO4 (Anastassiades et al, 2003;Wenaty et al, 2019). The mixture was centrifuged at 2500 rpm for 10 min and left to separate for further 5 min.…”

“…Separation and detection of OCPs were performed on a Hewlett Packard Gas Chromatography (Agilent 6890 Series gas chromatography system; from Agilent Technologies) equipped with an auto sampler (Agilent 7683 Series; from Agilent Technologies). For optimum separation, a dual capillary column system with two separate columns of different polarity and selectivity were used (Chrompac CPsil 5CB and J and W DB-17), Nominal length 50 and 60 m respectively, 0.25 mm ID, 0.25 µm film thickness) and coupled to two 63 Ni electron capture detectors (Agilent 6890 ECD) as described by Wenaty et al (2019). The following GC conditions were used; injector temperature: 280°C; injection volume: 2 µL; injector mode: splitless; purge flow: 42 mL/min; purge time: 0.60 min; carrier gas: Helium; constant flow: 2.0 and 1.3 mL/min respectively and make up gas: Nitrogen.…”

“…The temperature programme was 90°C held for 2.0 min; 30°C/min increased to 170°C held for 7.5 min; 2.0°C/min increased to 185°C; 3.0°C/min increased to 220°C held for 15 min; 3.0°C/min increased to 255°C held for 2.0 min and 5.0°C/min increased to 280°C held for 10 min. The detector temperature was 300°C (Wenaty et al, 2019).…”