Association between heavy metal uptake and growth and reproduction in the anecic earthworm, Alma nilotica (Grube 1855).

Elevated heavy metal concentrations in soils are a cause for concern as they are hazardous to soil organisms including earthworms which are considered as ecosystem engineers. Current ecotoxicity tests predominantly use temperate earthworm species, and thus there is the need to include a broader genera of native species to improve ecological risk assessment. Alma nilotica, is a tropical anecic earthworm species that survives well under laboratory conditions and has potential for use in ecotoxicology testing but lacks published toxicity data for important pollutants. Growth and reproduction bioassays were carried out with A. nilotica to determine the relationship between the concentrations of Cu, Zn, Pb and Cr in spiked soils and their bioaccumulation and toxic effects. Positive linear relationships were found between soil-metal and internal earthworm-metal concentrations. Cu did not inhibit growth up to 35 days of exposure but became toxic with longer exposure duration. Zn was not regulated by A. nilotica although it is an essential metal that is well regulated by Eisenia sp. commonly used in standard ecotoxicity tests, showing differences in metal regulation by earthworms of different ecological categories. Based on bioaccumulation factors (BAFs), growth inhibition and reproduction effects the metals were ranked in decreasing toxicity as Pb > Cr > Zn > Cu. The mean 20% Internal Effects Concentrations (IEC20s) for reproduction were 1.04, 2.9, 8.3 and 224.2 mg metal kg-1 earthworm for Pb, Cr, Zn and Cu respectively. These data can contribute to the improvement of metal risk assessment particularly in tropical contexts.

Effects of Electronic and Electrical Waste-Contaminated Soils on Growth and Reproduction of Earthworm (Alma nilotica).

Informal recycling of electronic waste (e-waste) contaminates local environments with metals and other organic compounds. The adverse effects on native earthworm populations are poorly understood. The objective of the present study was to determine metal concentrations in soils from e-waste activity sites in Douala (Cameroon) and assess the effects of these soils on the growth and reproduction of the local earthworm, Alma nilotica. Concentrations of nine metals (arsenic [As], cadmium [Cd], cobalt [Co], chromium [Cr], copper [Cu], mercury [Hg], nickel [Ni], lead [Pb], and zinc [Zn]) were measured in soil samples collected from eight e-waste activity and two non-e-waste sites. Earthworms were then exposed to these soils in the laboratory following test guidelines of the Organisation for Economic Co-operation and Development. Metal concentrations in the e-waste-contaminated soils were significantly higher than in the non-e-waste soils. The e-waste soils were found to have a different soil metal profile (Cu > Pb > Zn > Cr > Ni > Co > As > Cd > Hg) from that of the non-e-waste soils (Zn > Cr > Cu > Pb > Ni > As > Cd > Co > Hg). Earthworm growth and reproduction were significantly inhibited in organisms exposed to soils from e-waste sites. Reproduction was particularly affected, with a mean of 8 ± 5.6 offspring/10 worms in the e-waste-exposed worm groups compared with 90.5 ± 0.7 in non-e-waste soil worms. Notably, earthworm growth recovered during depuration in clean soil, indicating the possibility of remediation activities. The results demonstrate that soils at e-waste sites can affect the health of resident worm populations, which may be more sensitive than temperate species. They also highlight the potential of a bioassay-based approach in monitoring risks at e-waste sites. Environ Toxicol Chem 2022;41:287-297. © 2021 SETAC.

Soil Contamination and Bioaccumulation of Heavy Metals by a Tropical Earthworm Species (Alma nilotica) at Informal E-Waste Recycling Sites in Douala, Cameroon.

Soil contamination at electronic waste (e-waste) recycling sites is pervasive, though many locations have yet to be studied. While such contamination can present risks to soil organisms, little is known on the risks to native species. The objective of the present study was to assess soil contamination by heavy metals at e-waste recycling sites, and the potential of Alma nilotica, a native earthworm species, to bioaccumulate these metals. Soil samples collected from eight informal e-waste recycling sites and two non-e-waste sites in Douala, Cameroon, were analyzed for metal content. Metal concentrations in earthworm juveniles exposed to the soils for 21 days followed by a 14-day post-exposure period were measured weekly. Mean soil metal concentrations at e-waste sites ranked as Cu > Pb > Zn > Hg > Ni > As > Cd > Co > Cr. Based on contamination factors, soil contamination ranged from "moderate" (Cr), through "considerable" (Co and Cd), to "very high" for the rest of the metals. Based on the modified degree of contamination and risk index, all e-waste sites had "ultra-high" contamination with Ni, Pb, and Zn posing very high ecological risks and Bonaberi being the most contaminated site. There was a positive correlation between soil metal concentrations and metal accumulation (retention) by eathworms, but Hg and Co had the highest bioaccumulation factors (BAFs) despite having low soil concentrations. These results document that e-waste sites in Douala are contaminated with metals and that native earthworm species can bioaccumulate the studied metals at levels that could account for the toxic effects earlier recorded. With e-waste recycling growing worldwide, there is a need for more data, especially from understudied locations. Environ Toxicol Chem 2022;41:356-368. © 2021 SETAC.