Using X-ray microtomography to characterize the burrowing behaviour of earthworms in heterogeneously polluted soils

International audienceLarge amounts of chemicals are released into soil environments due to human activities, thereby harming organisms and their habitats. Earthworms are important bioindicators for chemical risk assessments of soil ecosystems, but the question remains of how they respond to different patterns of pollution. Laboratory experiments in soil mesocosms were carried out to observe changes in the burrowing behaviour of two earthworm species (Aporrectodea caliginosa and Lumbricus terrestris) with regard to different spatial distributions of benzo(a)pyrene, cadmium and copper, using X-ray computed microtomography (μCT). This is, to our knowledge, the first contribution of μCT to study earthworm behaviour in heterogeneously multi-polluted soils. Columns (14 × 30 cm) were filled with a silt loam soil and packed to represent two scenarios of heterogeneous pollution: a) ‘binary’, containing polluted soil in the low half part and unpolluted soil on top; and b) ‘patches’, containing small portions of polluted soil randomly placed into an unpolluted matrix. Earthworms were introduced individually in the columns and left in climatic chambers for 7 weeks. μCT images revealed that earthworms avoided the polluted zones differently (e.g. A. caliginosa>L. terrestris, ‘binary’ configuration). Individuals of L. terrestris that entered polluted areas showed a lower burrowing activity (volume and length of the burrow system) than those that did not enter. The presence of ‘patches’ of polluted soil did not cause a reduction of the burrowing activity such as that found in the ‘binary’ columns, although earthworms showed avoidance. Our results indicate that pollutants had a greater effect on earthworms’ burrowing behaviour in the presence of larger portions of contaminated soil compared with small random ones. The more evident avoidance behaviour of A. caliginosa pinpoints its usefulness in toxicity bioassays based on avoidance patterns, but questions its use in assays based on bioaccumulation of pollutants in tissues, for which L. terrestris may perform better

Editorial : Celebrating the work of Early Career Researchers in Soil Science

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Microbial-Assisted Phytoremediation: A Convenient Use of Plant and Microbes to Clean Up Soils

Environmental pollution by metal(loid)s (e.g., heavy metals—HMs) is a severe problem worldwide, as soils and aquatic resources became increasingly contaminated, threatening land ecosystems, surface and groundwater, as well as food safety and human health. The primary sources contributing to this extended pollution are anthropogenic inputs related to the burning of fossil fuels, mining and continued industrial activities, disposal of municipal solid wastes and wastewater discharges or use for irrigation, and excessive utilization of fertilizers and pesticides. A consequence of these anthropogenic activities is an increase of contaminated areas, which should be remediated to prevent or mitigate transfer of contaminants into terrestrial, atmospheric, or aquatic environments. Point and diffuse contamination by organic and inorganic pollutants causes wide concerns, and intentional or accidental introduction of these substances in the environment may represent serious impacts on public health