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 topics, especially in native species. The objective of this study was to increase understanding of soil contamination by heavy metals at e-waste recycling sites, and the amount that these metals bioaccumulate in Alma nilotica, a tropical earthworm species. Soil samples were collected from 8 informal e-waste recycling sites and 2 reference sites in Douala, Cameroon and analyzed for metals content via Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The resulting concentrations could be rank ordered as Cu > Pb > Zn > Hg > Ni > As > Cd > Co > Cr. The concentrations were significantly higher in e-waste sites compared to reference sites. Based on contamination factors the soils ranged from 'moderate' to 'very high'. Based on the modified degree of contamination indice all soils were classified as 'ultra-high'; and the order of metal ecological risk index was Zn > Pb > Ni > Hg > Cu > Cr > Co > Cd > As. There was a positive correlation between soil metal concentrations and earthworm accumulation though metals with higher soil concentrations tended to have lower bioaccumulation factors (BAFs). Only Hg and Co had BAFs >1. These results document that e-waste sites in Douala are contaminated with metals, and that native earthworm species can bioaccumulate relatively high amounts. With e-waste recycling growing worldwide, there is a need for more data especially from understudied locations and native species that may be impacted. This article is protected by copyright. All rights reserved.