Evaluation of Heavy Metals in Public Refuse Dumpsites in Nsukka Metropolis and their Faunal Implications

Abstract

This study assessed the concentrations of lead, chromium, iron, manganese, zinc, cadmium and copper in soil and dumpsite fauna as well as some environmental properties of soils collected from open dumpsites in Nsukka metropolis, Enugu State Nigeria. Sampling was conducted at all the open refuse dumpsites from January to March, 2017 (for dry season collection) and June to August, 2017 (for wet season collection). Soil samples from each of the dump sites were collected randomly at the depth of 15cm and the dumpsite fauna found around each of these dump sites were also sampled. Heavy metals in soil samples and dumpsite fauna were determined using Varian AA240 Atomic Absorption Spectrophometer (AAS). Environmental properties of the soil samples evaluated were soil pH, soil temperature, soil moisture and particle size distribution. Dumpsite fauna composition in the dumpsite, Percentage abundance, diversity, evenness, and richness were calculated using Simpson’s index, Gini-Simpson, Reciprocal Simpson, Shannon-Wiener diversity index, Modified Shannon-Wienner index, Berger-Parker index, McIntosh index, Margalef index, Menhinick index, Hill’s family of numbers, ShePbons index, Heip index, Pielo’s index and Simpson’s index of evenness. Six species of the dumpsite fauna were analyzed for heavy metal accumulation. Bioaccumulation of heavy metals in the dumpsite fauna was evaluated using US EPA Bioaccummulation factor (BAF) formula. Results indicated that the soil samples were moderately acidic ranging from 5.70 to 6.82, soil temperature ranged 25.03 – 29.67oC and moisture content 2.23 – 7.66%. Meanwhile the particle size distribution in the sand contents (40 – 55%) was higher than silt and clay. Throughout the duration of the study, total number of organisms collected from the dumpsites was 3,165. All the fauna collected belong to the following orders: Hymenoptera, Diptera, Orthoptera, Hemiptera, Araneae, Scorpiones, Coleoptera, Anura and Lepidoptera. Musca domestica had the highest number of organisms sampled while Heterometrus sp. was the lowest. Environmental properties of soil and heavy metals concentrations at the dumpsites showed variations both monthly and seasonally. The rank profile of heavy metals in the dumpsites soil was Fe > Zn > Mn > Cu > Cr > Pb > Cd. Among the dumpsites, the heavy metal concentrations was ranked Obimo > Ikenga Hotel > UNN > Obukpa. Among the heavy metals analyzed in the soil samples, Fe had the highest concentration of 21.08 ± 0.01mg/kg from Ikenga Hotel dumpsite while Cd was the lowest heavy metal that occurred (1.15 ± 0.30mg/kg) at UNN dumpsite. Concentrations of heavy metals in the dumpsite fauna ranked Fe > Zn > Mn > Pb > Cd > Cu > Cr for the dry season while the wet season concentrations ranked Fe > Zn > Mn > Cu > Pb > Cr > Cd. Z. variegatus had the highest Fe occurrence (16.04 ± 0.47 mg/kg) among all the dumpsite fauna studied. Rabiosa spp. had the lowest heavy metal occurrence of Cd and Pb (0.00 ± 0.00 mg/kg). The findings of the study showed that the concentrations of heavy metals in soil were generally far below the maximum permissible limits of a soil by Federal Environmental Protection Agency, European Regulatory Standards and United States Environmental Protection Agency standards.