Interactions of trace metals with bacteria and fungi in selected agricultural soils of Egbema Kingdom, Warri North, Delta state, Nigeria

Ecotoxicity of thallium to two soil animal species with different niches and modification by organic materials

Soil thallium (Tl) contamination is of major public concern but little is known about soil Tl ecological toxicity or potential ecological remediation strategies. Here, two soil animal species with different ecological niches, Folsomia candida and Enchytraeus crypticus, were used to test Tl toxicity and modification by exogenous organic materials (i.e. maize straw and biochar). The endpoints of Tl ecotoxicity to F. candida and E. crypticus were studied at two biological levels, i.e., the individual (body Tl concentrations) and the population (survival, reproduction, and growth). Thallium concentrations in F. candida and E. crypticus increased with increasing soil Tl concentration, and their survival and reproduction rates decreased with increasing soil Tl concentration. The LC50 value of Tl effects on F. candida mortality (28 d) was 24.0 mg kg-1 and the EC50 value of reproduction inhibition was 6.51 mg kg-1. The corresponding values were 4.15 mg kg-1 and 2.31 mg kg-1 respectively for E. crypticus showing higher sensitivity to soil Tl than F. candida. These effective values are comparable to or much lower than the environmental Tl concentrations in field soils, suggesting high potential ecological risk. Both biochar and straw can decrease animal body Tl concentrations in different ways, i.e. reducing Tl availability or offering clean food sources, and addition of exogenous organic materials clearly mitigated Tl ecotoxicity in highly polluted soil. The results highlight the potential Tl ecological risk to soil animals and the potential use of organic materials to control the toxicity.

The Effects of Heavy Metal Pollution on Collembola in Urban Soils and Associated Recovery Using Biochar Remediation: A Review

Heavy metal pollution in urban soil continues to be a global issue that poses a serious hazard to invertebrates and human lives through oral ingestion and inhalation of soil particles. Though the toxicity of several heavy metals on invertebrates like Collembola has been studied, lead (Pb) and cadmium (Cd) have been extensively studied due to their high toxicity to collembolans. As a ubiquitous soil organism all over the world, collembolans have been used as a model species to study the effects of heavy metals on invertebrate communities. To reduce the effects of heavy metals on ecosystem functions, biotic and abiotic measures have been used for heavy metal remediation; biochar seems to be the most effective approach that not only increases the physical absorption of heavy metals but also indirectly benefits soil organisms. In this study, we briefly reviewed the application of biochar in Pb and Cd polluted soil and showed its potential in soil remediation. Furthermore, we outlined the potentially toxic effects of Pb- and Cd-polluted urban soil on the collembolan species. We searched peer-reviewed publications that investigated: (1) the level of Pb and Cd contamination on urban soil in different cities around the world; and (2) the different sources of Pb and Cd as well as factors influencing their toxicity to collembolan communities. The obtained information offers new perspectives on the interactions and effects between collembolans, Pb, and Cd, and their remediation in urban soils.

Health risk estimations and geospatial mapping of trace metals in soil samples around automobile mechanic workshops in Benin city, Nigeria

This study was carried out to assess the distribution of trace metals in soil samples from selected automobile mechanic workshops (AMWs) in Benin City, spatially map the concentrations and estimate the health risk indices for the exposed populace. Topsoil samples were collected from twenty-one (21) AMWs in Benin City in 3 composites for three months at each station. Soil samples were analyzed for heavy metals (Pb, Cd, Fe, Cu, Ni, Cr, and Zn) using Atomic Absorption Spectrophotometer. The non-carcinogenic risks caused by exposure to the metals were insignificant, characterized by in mean values of hazard quotient (HQ) and hazard index (HI) below one (1) in adults and children. Carcinogenic risk (CR) occurred only in the children exposed to nickel through ingestion; attributable to ingestion. In adults and children, the risks associated with the uptake routes were in the order of ingestion > dermal contact > inhalation. The hazard index (HI) values of heavy metals for children and adults decreased in the order of Pb > Cr > Cd > Cu > Zn > Ni and were all lower than one (1), which indicated that the children and adults were not at non-carcinogenic risk. The contamination factors (CF) of all metals analyzed were lower than one (1), suggesting low contamination. The average CF decreased in the order of Pb (0.3715) > Zn (0.14) > Cu (0.087) > Cr (0.013) > Ni (0.01) > Fe (0.0007). Potential ecological risks of the trace metals in soils of these workshops revealed low pollution of the soils by the metals. Results indicated that the three routes of uptake in adults and children decreased in the order of ingestion > dermal > inhalation. The non-carcinogenic risks posed by metals to the children and adults were insignificant. Ingested nickel however posed potential carcinogenic risk to only the children. The toxicodynamics of heavy metals in the soil profile demonstrated in this study could be a vital information for future studies and decisions on the management of the health and environment of the study area.