Ecotoxicological assessments of biochar additions to soil employing earthworm species Eisenia fetida and Lumbricus terrestris

Abstract

Biochar is the degradation-resistant product generated by the pyrolysis of organic materials and is produced for the intended use of land application in order to promote carbon sequestration and soil improvement. However, despite the many potential benefits biochar application offers, it is important to quantify any ecological impacts that may result from soil amendment in order to avoid potentially causing negative effects upon soil biota which are crucial in the many ecosystem services provided by soil. Any impacts on earthworms in particular are important to evaluate because of their pivotal role in organic matter breakdown, nutrient cycling and soil formation. In this study, we conducted a series of ecotoxicological assays to determine lethal and sublethal (avoidance, mass change and moisture content) effects of heavy biochar applications that reflect levels that may be used in soil restoration efforts. Two earthworm species, Eisenia fetida, an epigeic species, and Lumbricus terrestris, an anecic species, were utilised as test organisms. Two types of biochar, produced from wheat straw and rice husk feedstocks, respectively, were applied to OECD artificial soil and to a natural soil (Kettering loam) at rates of up to 20% w/w. The influence of biochar application on soil porewater chloride, fluoride and phosphate concentrations was also assessed. The biochar applications induced only a subtle level of avoidance behaviour while effects on survival over a 4-week exposure period were inconsistent. However, death and physical damage to some individual earthworms at high biochar application rates were observed, the mechanisms and processes leading to which should be investigated further. Earthworm development (mean mass change over time) proved to be a more sensitive measure, revealing negative effects on L. terrestris at 10% and 20% (w/w) wheat biochar applications in OECD soil and at 20% (w/w) applications of both biochars in Kettering loam. The moisture content of E. fetida remained remarkably consistent across all treatments (~82%), indicating that this is not a sensitive measure of effects. The high rates of biochar application resulted in increased chloride (2 to 3-fold) and phosphate (100-fold) concentrations in simulated soil porewaters, which has important implications for soil fertility and production but also for environmental management.

Impact of Eisenia fetida earthworms and biochar on potentially toxic element mobility and health of a contaminated soil

“…These results highlight that the use of biochar for soil restoration may reduce the chance of PTEs entering the terrestrial food web through earthworms, if they are predated by higher animals (i.e. mammals, birds, reptiles and amphibians) (Elliston and Oliver, 2020). Only Sb-BAF increased for earthworms grown in the amended soils (i.e.…”

Biochar and Its Broad Impacts in Soil Quality and Fertility, Nutrient Leaching and Crop Productivity: A Review

“…In aquatic ecosystems, biochar was shown to increase the leaching of dissolved organic carbon, and this apparently reduced the light penetration in lakes [131,191]. Finally, studies have shown that biochar application disturbed the abundance of earthworms (Lumbricus terrestris), which play a key role in soil formation, breakdown of organic matter, and nutrient cycling in agroecosystems [192].…”

Investigating the Sublethal Effects of Cannabis sativa on Earthworms and Trematode Cercariae

“…As such, changes in metrics like reproduction, mortality, growth, and behaviour are easy to test experimentally, making E. fetida an ideal candidate for examining the potential lethal and sublethal effects of environmental contaminants. To date, E. fetida have been used to examine the effects of many potential environmental contaminants, including compounds like heavy metals, pesticides, and artificial soil (Yasmin & D'Souza, 2007;Garcia-Velasco et al 2017;Elliston & Oliver, 2019). Although some studies have tested the effects of various applications of C. sativa on E. fetida and found that there are no short-term lethal effects (Chauhan & Joshi, 2010;Benelli et al 2018), potential sublethal effects on reproduction, growth, and behaviour remain unknown.…”