Avoidance, biomass and survival response of soil dwelling (endogeic) earthworms to OECD artificial soil: potential implications for earthworm ecotoxicology

Ecotoxicology, Mar 2017

Soil dwelling earthworms are now adopted more widely in ecotoxicology, so it is vital to establish if standardised test parameters remain applicable. The main aim of this study was to determine the influence of OECD artificial soil on selected soil-dwelling, endogeic earthworm species. In an initial experiment, biomass change in mature Allolobophora chlorotica was recorded in Standard OECD Artificial Soil (AS) and also in Kettering Loam (KL). In a second experiment, avoidance behaviour was recorded in a linear gradient with varying proportions of AS and KL (100% AS, 75% AS + 25% KL, 50% KS + 50% KL, 25% AS + 75% KL, 100% KL) with either A. chlorotica or Octolasion cyaneum. Results showed a significant decrease in A. chlorotica biomass in AS relative to KL, and in the linear gradient, both earthworm species preferentially occupied sections containing higher proportions of KL over AS. Soil texture and specifically % composition and particle size of sand are proposed as key factors that influenced observed results. This research suggests that more suitable substrates are required for ecotoxicology tests with soil dwelling earthworms.

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Avoidance, biomass and survival response of soil dwelling (endogeic) earthworms to OECD artificial soil: potential implications for earthworm ecotoxicology

Ecotoxicology Avoidance, biomass and survival response of soil dwelling (endogeic) earthworms to OECD artificial soil: potential implications for earthworm ecotoxicology C. Brami 0 ● A. R. Glover 0 ● K. R. Butt 0 ● C. N. Lowe 0 0 School of Forensic and Applied Sciences, University of Central Lancashire , Preston PR1 2HE , UK Soil dwelling earthworms are now adopted more widely in ecotoxicology, so it is vital to establish if standardised test parameters remain applicable. The main aim of this study was to determine the influence of OECD artificial soil on selected soil-dwelling, endogeic earthworm species. In an initial experiment, biomass change in mature Allolobophora chlorotica was recorded in Standard OECD Artificial Soil (AS) and also in Kettering Loam (KL). In a second experiment, avoidance behaviour was recorded in a linear gradient with varying proportions of AS and KL (100% AS, 75% AS + 25% KL, 50% KS + 50% KL, 25% AS + 75% KL, 100% KL) with either A. chlorotica or Octolasion cyaneum. Results showed a significant decrease in A. chlorotica biomass in AS relative to KL, and in the linear gradient, both earthworm species preferentially occupied sections containing higher proportions of KL over AS. Soil texture and specifically % composition and particle size of sand are proposed as key factors that influenced observed results. This research suggests that more suitable substrates are required for ecotoxicology tests with soil dwelling earthworms. Artificial soil ● Avoidance test ● Ecotoxicology ●; Soil dwelling earthworms Introduction The potential for earthworms as bio-indicators of environmental quality is widely recognised (reviewed by Fründ et al. 2011 ). Litter dwelling (compost) earthworms have been widely adopted for use in both acute and chronic ecotoxicological studies, with Eisenia fetida proposed in a number of standardised tests (OECD Acute Toxicity Test (OECD 1984) , USEPA OCSPP 850.3100 Earthworm Subchronic toxicity test (USEPA 2012) , ISO 11268-1:2012 acute toxicity test (ISO 2015) and ISO 17512-1:2008 avoidance test (ISO 2012) . This is due to a short life cycle, high fecundity, relative ease of cultivation and commercial availability. However, the use of such species in ecotoxicology has been openly questioned (Lukkari et al. 2005; Lowe and Butt 2007) as they do not inhabit mineral soil, have a limited distribution associated with naturally occurring organic matter and are therefore considered to have limited ecological relevance. The use of soil dwelling species is increasingly advocated (Svendsen et al. 2005; Suthar et al. 2008; Butt and Lowe 2011) particularly as perceived issues associated with maintenance and culture have been overcome (Lowe and Butt 2005) . Artificial soils are often preferred to natural soils in standardised toxicity tests as they allow conformity in, and comparability of results, are available throughout the year and do not contain organisms or pollutants that can influence the test. In standardised earthworm-related tests (e.g. ISO 17512-1:2008, ISO 11268-1:2012) , OECD artificial soil (AS) is recommended. However, the use of OECD AS may not always be appropriate. Hofman et al. (2009) refer to several specific issues including: (1) validity of test result extrapolation to field conditions, as the properties of OECD AS are substantially different to natural soils; (2) variation in toxicity results between laboratories employing OECD AS, as the specific properties of each component are not specified, even though the component composition of AS is strictly defined. A number of researchers have sought to address the second issue (Bouwman 2007) , however such studies have focussed on development of substrates for epigeic earthworm species. Several studies (e.g. Shoults-Wilson et al. 2011; Loureiro et al. 2005) have found that avoidance of contaminants by earthworms can be equivalent to or more sensitive than traditional endpoints, such as biomass gain/loss and mortality. Only one standardized avoidance test (ISO 17512-1, 2008) has been developed and recommends the use of E. fetida and E. andrei. This standard details the methods for a two-section and also a six-section avoidance test, with the latter difficult to set up and rarely used. Lowe et al. (2016) developed an avoidance test that allows for the establishment of a linear pollution gradient within rectangular mesocosms (troughs) that are simpler to establish than the six-section chamber test and also allow for a larger range of concentrations than the two-section chamber design. As soil dwelling earthworms are adopted more widely in ecotoxicology, it is important to establish if standardised test parameters remain applicable. Two-section avoidance tests have been used to study the influence of soil properties (Natal-da-Luz et al. 2008) , by manipulating OECD AS, but these have focused on epigeic rather than soil dwelling earthworms. The main aim of this study was to establis (...truncated)


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C. Brami, A. R. Glover, K. R. Butt, C. N. Lowe. Avoidance, biomass and survival response of soil dwelling (endogeic) earthworms to OECD artificial soil: potential implications for earthworm ecotoxicology, Ecotoxicology, 2017, pp. 576-579, Volume 26, Issue 4, DOI: 10.1007/s10646-017-1788-1