Toxicity assessment of wastewater treatment plant sludge using Caenorhabditis elegans

Globally, sewage sludge is produced in large quantities as a by-product in wastewater treatment plants (WWTPs), which have organic and inorganic contaminants. Due to its high caloric value, this sludge is used as manure in agricultural fields. For this, regular sludge monitoring is necessary to understand the potential risks and limit the release of toxic substances into the environment. To this end, heavy metals, pesticides, and polycyclic aromatic hydrocarbons (PAHs) were analysed in wet and dry sludge samples collected from the Bharwara WWTP in Lucknow for two consecutive years. Further, to determine the environmental impact of sludge, Caenorhabditis elegans was used, and end-points such as recovery, growth, and reproduction were studied. Our data revealed the presence of heavy metals, pesticides, and PAHs in the sludge samples. Exposure of worms to sludge did not impact the growth of the organism. However, recovery and reproduction were negatively impacted by exposure to wet sludge, while dry sludge had the opposite impact on the reproductive ability of worms. This study indicates that dry sludge processed under the sun has lower amounts of contaminants and is comparatively safer for test organisms, and C. elegans is an apt model for ecotoxicity assessment of sludge.