different times of exposure (7, 14 and 28 days) [32]. In that study, non-conservative
measures in whole tissue such as LPO (MDA content) and total antioxidant capacity
(TAC), as well as measures in coelomocyte/genotoxicity (TUNEL assay), were
related to metal partitioning in several subcellular fractions. Their conclusions
confirmed the lower sensibility of E. fetida to metal exposures and therefore the
need to include more ecologically relevant species in soil pollution assessment, as
suggested previously in other earthworm studies.
5 Biomarkers for Mixed Chemical Exposure
Under a realistic field scenario, soil-dwelling earthworms will experience multixenobiotic exposures which are likely to require the consideration of a comprehensive set of biomarkers, including those dealing with general stress. This was the case
of a field study in India using the earthworm Dichogaster curgensis as bioindicator
in which the targeted chemicals were a consequence of fly ash pollution (mostly
made of metals and polyhalogenated compounds). Amongst the biomarkers tested,
there were antioxidant CAT, SOD, GR, GPX and GST activities and LPO levels,
cytotoxicity, genotoxicity and histopathology as effect markers [33].
From a realistic perspective, and within the context of the usage of treated
wastewaters (TWWs) in agriculture of arid and semi-arid climate areas, E. fetida
was exposed to artificial soils irrigated with wastewater following different purification treatments [34]. The biomarkers of general stress, LMS (NRR assay) in
coelomocytes, and the specific one, MT content in whole tissue homogenates,
were measured after 28 days, and the authors claimed their approach proved suitable
for assessing toxicological safety in reclaimed wastewaters’ reuse [34]. Similarly,
the species E. andrei was selected under laboratory soil exposure conditions for the
potential use of TWW in agriculture, and a set of parameters involving enzymatic
activities (CAT, GST and AChE) and gene expression (cat and gst) were considered
as biomarkers in the exposed organisms [35]. The soil irrigated with an increasing
percentage of TWW caused a reduction of CAT and AChE activities, while GST
activity and LPO levels increased in the exposed earthworms, and the corresponding
gene expression (cat and gst) was significantly downregulated with respect to
controls. These researchers conducted the same type of study but considered natural
soils that had been irrigated with TWW in a country with water scarcity problems
(Tunisia) for an extended period of time: 1, 8 and 20 years [36]. The biomarkers
considered in the long-term study were coincident with those considered before, but
they also included genotoxicity (using micronuclei test). The longer exposures
(20 years) impacted more negatively on the earthworm fauna, seen as enhanced
genotoxicity, probably as a consequence of the higher metal and organic pollutant
load detected in the longer-term irrigated soil experience. The vermicompost earthworm E. eugeniae was exposed for 24 h to contaminated soil containing three
concentrations of several fertilisers and agrochemicals of concern in Indian agricultural soils, and the biomarkers measured comprised histology alterations, LPO
Biomarkers in Earthworms
325
measures in whole tissue such as LPO (MDA content) and total antioxidant capacity
(TAC), as well as measures in coelomocyte/genotoxicity (TUNEL assay), were
related to metal partitioning in several subcellular fractions. Their conclusions
confirmed the lower sensibility of E. fetida to metal exposures and therefore the
need to include more ecologically relevant species in soil pollution assessment, as
suggested previously in other earthworm studies.
5 Biomarkers for Mixed Chemical Exposure
Under a realistic field scenario, soil-dwelling earthworms will experience multixenobiotic exposures which are likely to require the consideration of a comprehensive set of biomarkers, including those dealing with general stress. This was the case
of a field study in India using the earthworm Dichogaster curgensis as bioindicator
in which the targeted chemicals were a consequence of fly ash pollution (mostly
made of metals and polyhalogenated compounds). Amongst the biomarkers tested,
there were antioxidant CAT, SOD, GR, GPX and GST activities and LPO levels,
cytotoxicity, genotoxicity and histopathology as effect markers [33].
From a realistic perspective, and within the context of the usage of treated
wastewaters (TWWs) in agriculture of arid and semi-arid climate areas, E. fetida
was exposed to artificial soils irrigated with wastewater following different purification treatments [34]. The biomarkers of general stress, LMS (NRR assay) in
coelomocytes, and the specific one, MT content in whole tissue homogenates,
were measured after 28 days, and the authors claimed their approach proved suitable
for assessing toxicological safety in reclaimed wastewaters’ reuse [34]. Similarly,
the species E. andrei was selected under laboratory soil exposure conditions for the
potential use of TWW in agriculture, and a set of parameters involving enzymatic
activities (CAT, GST and AChE) and gene expression (cat and gst) were considered
as biomarkers in the exposed organisms [35]. The soil irrigated with an increasing
percentage of TWW caused a reduction of CAT and AChE activities, while GST
activity and LPO levels increased in the exposed earthworms, and the corresponding
gene expression (cat and gst) was significantly downregulated with respect to
controls. These researchers conducted the same type of study but considered natural
soils that had been irrigated with TWW in a country with water scarcity problems
(Tunisia) for an extended period of time: 1, 8 and 20 years [36]. The biomarkers
considered in the long-term study were coincident with those considered before, but
they also included genotoxicity (using micronuclei test). The longer exposures
(20 years) impacted more negatively on the earthworm fauna, seen as enhanced
genotoxicity, probably as a consequence of the higher metal and organic pollutant
load detected in the longer-term irrigated soil experience. The vermicompost earthworm E. eugeniae was exposed for 24 h to contaminated soil containing three
concentrations of several fertilisers and agrochemicals of concern in Indian agricultural soils, and the biomarkers measured comprised histology alterations, LPO
Biomarkers in Earthworms
325