Ecotoxicological effects of coal fly ash on Daphnia magna: The effect of particulates and leached hazardous trace elements

Coal fly ash (CFA) derived from coal combustion can threaten aquatic ecosystems through both particulate matter and leached hazardous trace elements (HTEs). However, previous toxicity studies of CFA towards aquatic organisms mainly focused on the effects of leached HTEs. This study assessed the combined effects of CFA particulates (5 g·L -1 ) and their leachates on Daphnia magna . The immobility, reproduction, population size and structure of organisms were investigated. The hazard quotients (HQs) of respective HTEs and particulates were calculated. The overall HQs remained < 1, indicating 5 g·L -1 CFA system within the safe level. The correlation and HQ calculations identified leached Cr and As as the primary leaching contributors to chronic toxicity due to their relative high leachability. Hazard quotient (HQ) analysis showed that particulate fractions posed over 100-fold greater risk than leached HTEs. In terms of particulates size effects, 28-day chronic assays suggested fine particulates exposure led to the lowest EC 5 (0.001 g·L -1 ) of total reproduction, highest HQ-value (0.33), and maximum population reduction (16.4%), suggesting a size-dependent toxicity related to D. magna ’ s filter-feeding range (0.6-40 µm). The dominant role of particulates in ecotoxicity highlights the need to integrate particulate effects into CFA risk assessments and disposal strategies.