toxicogenomics and toxicotranscriptomics in earthworms will not be discussed here
as they have been accurately addressed elsewhere [16].
In addition to traditional biochemical markers, gene expression and
metabolomics are new molecular tools gaining importance in biomonitoring
although genetic changes and endogenous metabolite alterations should be translated
into protein and physiological consequences, respectively, to gain ecological relevance. In fact, to relate sub-individual molecular and biochemical modifications to
higher ecological consequences is one of the main objectives on the use of biomarkers for toxicity assessment. Therefore, studies aimed at linking responses at
different hierarchy biological levels are of the utmost relevance.
In earthworms, the organs/tissues selected for biomarker determinations mostly
refer to whole tissue homogenates due to constraints on the size of those most
frequently used as sentinels. Moreover, to consider the whole tissue is relevant as
it informs on the integrative response of the entire organism. In the case of larger
earthworms, such as L. terrestris, and for research purposes, the use of particular
organs/tissues has been encouraged as it discriminates the most sensitive ones to
particular exposures [7]. Nonetheless, for monitoring purposes which frequently
require sufficient biological tissue to perform a comprehensive set of complementary
measures, and in which the speed for processing large quantities of samples is
important, the use of earthworm whole tissue homogenates greatly simplifies the
protocol. In this sense, some studies have been centred on validating the whole tissue
approach in respect of more time-consuming accurate dissection techniques that
require more expertise. It is also worth stressing the interest in validating biomarkers
measured in whole tissue using traditional destructive tools with these same markers
measured using alternative conservative techniques in biological fluids
(e.g. coelomocytes). Some studies in earthworms are designed to achieve this goal
since, in addition to having an ethical value, they allow follow-up of exposures in the
same individuals and thus, reduce biological variability and the number of individuals required for experimentation. In this sense, the use of the coelomic fluid and the
well-developed nervous system of larger earthworms is the targeted non-destructive
matrix and will be discussed further.
In the next section, earthworm studies conducted using mostly biochemical biomarkers since 2014 will be described in relation to specific types of pollutants as
listed in Table 1. Only a few studies have addressed particular exposures to pharmaceuticals; thus, a consideration to other chemicals has been given. However,
general biomarker responses in terms of immune responses, oxidative stress and
neurotoxicity are expected due to exposure to pharmaceuticals as has been observed
in other invertebrate groups. Given the promising evidences with the incorporation
of biomarkers in the field of gene expression and metabolomics, some recent studies
including this approach will also be considered. An additional section will address
the importance of metabolism and metabolite identification in earthworms for two
main reasons: (1) it evidences the pathway of xenobiotic metabolism taking place
within the organism and (2) it identifies by-products with even greater potential
toxicity after their metabolism (metabolites) and therefore of the utmost importance
not only for the individual but also in terms of food chain transfer.
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M. Solé
as they have been accurately addressed elsewhere [16].
In addition to traditional biochemical markers, gene expression and
metabolomics are new molecular tools gaining importance in biomonitoring
although genetic changes and endogenous metabolite alterations should be translated
into protein and physiological consequences, respectively, to gain ecological relevance. In fact, to relate sub-individual molecular and biochemical modifications to
higher ecological consequences is one of the main objectives on the use of biomarkers for toxicity assessment. Therefore, studies aimed at linking responses at
different hierarchy biological levels are of the utmost relevance.
In earthworms, the organs/tissues selected for biomarker determinations mostly
refer to whole tissue homogenates due to constraints on the size of those most
frequently used as sentinels. Moreover, to consider the whole tissue is relevant as
it informs on the integrative response of the entire organism. In the case of larger
earthworms, such as L. terrestris, and for research purposes, the use of particular
organs/tissues has been encouraged as it discriminates the most sensitive ones to
particular exposures [7]. Nonetheless, for monitoring purposes which frequently
require sufficient biological tissue to perform a comprehensive set of complementary
measures, and in which the speed for processing large quantities of samples is
important, the use of earthworm whole tissue homogenates greatly simplifies the
protocol. In this sense, some studies have been centred on validating the whole tissue
approach in respect of more time-consuming accurate dissection techniques that
require more expertise. It is also worth stressing the interest in validating biomarkers
measured in whole tissue using traditional destructive tools with these same markers
measured using alternative conservative techniques in biological fluids
(e.g. coelomocytes). Some studies in earthworms are designed to achieve this goal
since, in addition to having an ethical value, they allow follow-up of exposures in the
same individuals and thus, reduce biological variability and the number of individuals required for experimentation. In this sense, the use of the coelomic fluid and the
well-developed nervous system of larger earthworms is the targeted non-destructive
matrix and will be discussed further.
In the next section, earthworm studies conducted using mostly biochemical biomarkers since 2014 will be described in relation to specific types of pollutants as
listed in Table 1. Only a few studies have addressed particular exposures to pharmaceuticals; thus, a consideration to other chemicals has been given. However,
general biomarker responses in terms of immune responses, oxidative stress and
neurotoxicity are expected due to exposure to pharmaceuticals as has been observed
in other invertebrate groups. Given the promising evidences with the incorporation
of biomarkers in the field of gene expression and metabolomics, some recent studies
including this approach will also be considered. An additional section will address
the importance of metabolism and metabolite identification in earthworms for two
main reasons: (1) it evidences the pathway of xenobiotic metabolism taking place
within the organism and (2) it identifies by-products with even greater potential
toxicity after their metabolism (metabolites) and therefore of the utmost importance
not only for the individual but also in terms of food chain transfer.
316
M. Solé