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)