Health risk assessment of mercury in Nile tilapia (Oreochromis niloticus) fed housefly maggots

The bioaccumulation of total mercury (THg) and methylmercury (MeHg) by housefly maggots (HM) during the conversion of food waste (vegetables and meat (VM) and rice waste) under various waste feed ratios were investigated. Subsequently, Nile tilapia (Oreochromis niloticus) were fed with the commercial feed, commercial dried HM, dried HM, and fresh HM, followed by a human health risk assessment of Hg via fish consumption. The THg concentrations of HM fed with food waste ranged from 39.5 to 100 μg kg−1 ww. Concentrations of MeHg in the maggots fed with 100 % vegetables and meat (VM) waste (13.7 ± 1.12 μg kg−1 ww) was significantly higher than that fed with other mixed ratios of rice waste and VM waste (p < 0.05). Concentrations of MeHg were positively correlated with the weight and lipid content of houseflies (p < 0.05). THg and MeHg concentrations in tilapia fed with the converted HM (dried and fresh HM) were 22.5 ± 6.50 μg kg−1 ww and 2.43 ± 0.36 μg kg−1 ww, respectively. There was no significant difference in MeHg between tilapia fed the four experiment diets (p > 0.05). Health risk assessment results indicated that mercury in tilapia fed the food waste-grown HM did not pose potential health risks to humans (target hazard quotient < 1). In conclusion, HM could convert food waste into high-quality and safe fish feeds for cultivating tilapia.