pesticides (oxon forms) and most polycyclic aromatic hydrocarbons (PAHs) and
phenoxy herbicides (phenol formation) by oxidative reactions mostly catalysed by
P450 enzymes. The authors from this former review concluded that in earthworms
the main metabolic processes are carried out by the cytochrome P450 family,
carboxylesterases (phase I oxidation and hydrolysis reactions, respectively) and
glutathione S-transferases (conjugation phase II metabolism) although in quantitative terms they are less represented than in fish or higher vertebrates. Moreover, CEand GST-catalysed reactions are mainly detoxification pathways, whereas those by
phase I cytochrome P450 enzymes can lead to more toxic metabolites.
The identification of metabolites can also shed light onto the metabolic pathways
experienced by the parental chemicals in earthworms and the further assessment of
their associated toxicities. The study by Qin et al. [78] on the toxicity of the two
racemic forms of the insecticide fipronil identified by means of HPLC-MS/MS
analyses several phase I metabolites resulting from oxidation (sulphide), reduction
(sulphone) and hydrolysis (amide) and revealing the S-fipronil form was more toxic
than the R-fipronil one. Other phase II conjugation mechanisms significant in
mammalian systems (conjugation with glucose, glucuronic acid or sulphate) are
not regarded as prevalent in earthworms. However, with more recent technological
advances in analytical methodologies, metabolite identification has greatly
improved. In soil-dwelling organisms, O-methylation seems to be the preferred
detoxification strategy, at least for phenolic compounds such as TBBPA [62]. Exposure to the OP flame retardant TPhP in the 28-day soil microcosm experience with
the earthworm P. excavatus formerly described [70] identified several phase I and
phase II metabolites by untargeted LC-QTOF methods, with the glucoside conjugates more abundant than the thiol-derived ones. A suggestion of potential metabolite formation in earthworms could also be provided by the enzymatic responses
altered after the exposures and its confirmation by the application of state-of-the-art
analytical technologies. This is the case provided by the [69] study formerly
described in relation to EtFOSE exposures in which an elevation of GST activities
was indicative of this conjugation pathway taking place and its further confirmation
with metabolite identification by GC-MS.
The importance of metabolite identification for further toxicity assessment was
given by the Liu et al. [26] study on dinotefuran (a neonicotinoid insecticide) and
two of their main metabolites 1-methyl-3-(tetrahydro-3-furylmethyl) urea (UF) and
1-methyl-3-(tetrahydro-3-furylmethyl) guanidium dihydrogen (DN) exposures in
E. fetida. The toxic effects induced by UF and DN metabolites showed a significant
dose-effect and time-effect correlation. By increasing the concentrations (0.1–2 mg kg
À1 ) and time (up to 28 days), more UF and DN were accumulated in
earthworms, and these identified metabolites were responsible for changes in SOD
and CAT activities, damage in lipid and nucleic acid and abnormal expression of
Hsp70 and ANN genes confirming their toxic properties. More recently, an environmentally relevant study applied suspect and non-target screening QTOF-MS
technology to identify 60 parental pesticides and pharmaceuticals and at least
50 of its transformation products in wastewater, resulting from biotic and abiotic
degradation processes, and its further toxicity assessment was applied using the
ECOSAR model [79].
332
M. Solé
phenoxy herbicides (phenol formation) by oxidative reactions mostly catalysed by
P450 enzymes. The authors from this former review concluded that in earthworms
the main metabolic processes are carried out by the cytochrome P450 family,
carboxylesterases (phase I oxidation and hydrolysis reactions, respectively) and
glutathione S-transferases (conjugation phase II metabolism) although in quantitative terms they are less represented than in fish or higher vertebrates. Moreover, CEand GST-catalysed reactions are mainly detoxification pathways, whereas those by
phase I cytochrome P450 enzymes can lead to more toxic metabolites.
The identification of metabolites can also shed light onto the metabolic pathways
experienced by the parental chemicals in earthworms and the further assessment of
their associated toxicities. The study by Qin et al. [78] on the toxicity of the two
racemic forms of the insecticide fipronil identified by means of HPLC-MS/MS
analyses several phase I metabolites resulting from oxidation (sulphide), reduction
(sulphone) and hydrolysis (amide) and revealing the S-fipronil form was more toxic
than the R-fipronil one. Other phase II conjugation mechanisms significant in
mammalian systems (conjugation with glucose, glucuronic acid or sulphate) are
not regarded as prevalent in earthworms. However, with more recent technological
advances in analytical methodologies, metabolite identification has greatly
improved. In soil-dwelling organisms, O-methylation seems to be the preferred
detoxification strategy, at least for phenolic compounds such as TBBPA [62]. Exposure to the OP flame retardant TPhP in the 28-day soil microcosm experience with
the earthworm P. excavatus formerly described [70] identified several phase I and
phase II metabolites by untargeted LC-QTOF methods, with the glucoside conjugates more abundant than the thiol-derived ones. A suggestion of potential metabolite formation in earthworms could also be provided by the enzymatic responses
altered after the exposures and its confirmation by the application of state-of-the-art
analytical technologies. This is the case provided by the [69] study formerly
described in relation to EtFOSE exposures in which an elevation of GST activities
was indicative of this conjugation pathway taking place and its further confirmation
with metabolite identification by GC-MS.
The importance of metabolite identification for further toxicity assessment was
given by the Liu et al. [26] study on dinotefuran (a neonicotinoid insecticide) and
two of their main metabolites 1-methyl-3-(tetrahydro-3-furylmethyl) urea (UF) and
1-methyl-3-(tetrahydro-3-furylmethyl) guanidium dihydrogen (DN) exposures in
E. fetida. The toxic effects induced by UF and DN metabolites showed a significant
dose-effect and time-effect correlation. By increasing the concentrations (0.1–2 mg kg
À1 ) and time (up to 28 days), more UF and DN were accumulated in
earthworms, and these identified metabolites were responsible for changes in SOD
and CAT activities, damage in lipid and nucleic acid and abnormal expression of
Hsp70 and ANN genes confirming their toxic properties. More recently, an environmentally relevant study applied suspect and non-target screening QTOF-MS
technology to identify 60 parental pesticides and pharmaceuticals and at least
50 of its transformation products in wastewater, resulting from biotic and abiotic
degradation processes, and its further toxicity assessment was applied using the
ECOSAR model [79].
332
M. Solé