Biochemical, metabolic, and behavioural responses and recovery of Daphnia magna after exposure to an organophosphate
Introduction
Environmental disturbances, for example exposure to toxicants, affect organisms initially at the suborganismal level and might then affect higher levels of biological organisation, such as the populations or communities.
Effects at the suborganismal level can act as early warning signals of the presence of xenobiotics and provide detailed information on how chemicals interact with target sites. Effects at the level of the individual are indicative of the overall fitness of organisms, and might spread to the population and community levels depending on their severity and the compensatory mechanisms employed by the organisms that have been exposed. The responses at different levels of organisation can provide useful information for identifying and quantifying the effects of toxicants on biological systems (Maltby, 1999). To understand the processes involved, an approach is recommended in which the suborganismal impact of sublethal stress is related to higher-order biological consequences at the individual and population levels (Picado et al., 2007).
Numerous studies on the biological effects of toxicants in aquatic ecosystems have focused on invertebrates. Among them, studies of daphnids are highly relevant because these organisms are important components of freshwater food chains; they consume algae and other small organisms, and are in turn prey for small fish and other carnivorous aquatic animals. They are used commonly to assess the hazard or risk of contaminants (ISO (International Standard Organization), 1989), and are particularly useful for that purpose because of their short lifespan and reproductive capabilities, and also because of their sensitivity to toxic compounds including metal and organic compounds (Wogram and Liess, 2001). For example, Daphnia magna are known to be sensitive to organophosphates (OPs) (Guilhermino et al., 1996; Barata et al., 2001). They are also useful for comparing the effects of toxicants on various endpoints at different levels of biological organisation. This is particularly beneficial because there have been few reports that have compared the effects that occur at the suborganismal level with those at higher levels for invertebrates. The few exceptions include studies that link cellular energy markers (De Coen and Janssen, 2003; Durou et al., 2007), metallothionein and DNA damage (De Coen and Janssen, 2003; Neuparth et al., 2005; Costa et al., 2005), and inhibition of cholinesterases (ChE) (Duquesne, 2006) with effects at the population level. In the latter study, pulse exposure to a moderate level of OP induced a decrease in ChE activity in D. magna. Although the decrease in ChE activity was transient, effects occurred at the population level (for example, in terms of reproductive performance and population growth rate) above a threshold concentration.
In contrast to the above, comparisons of the effects that occur at the suborganismal and organismal levels have been reported for a large number of invertebrate species (Livingstone, 2001; Hyne and Maher, 2003; Galloway et al., 2004); in these reports the endpoint was usually the death of the organism. However, sublethal endpoints, such as changes in reproduction or feeding activity, are much more useful because, potentially, they offer a more sensitive and ecologically relevant alternative to lethality (McWilliam and Baird, 2002). Sublethal disturbances that occur commonly in the environment can lead to long-term changes at the population and community levels. In the case of pesticide stress, the widely used OPs, for example, exert their toxicity at the suborganismal level by inhibiting cholinesterases (ChE) and carboxylesterases. Inhibition of ChE has been observed in many species of aquatic invertebrates (e.g. Day and Scott, 1990; Sturm and Hansen, 1999; Diamantino et al., 2000; Barata et al., 2001, Barata et al., 2004; Guilhermino et al. 1996). The relationship between ChE inhibition and mortality is generally less well distinct in invertebrates than in fish (Fulton and Key, 2001).
A more detailed characterisation of the responses of various parameters to pulse exposure to a sublethal level of OP at the suborganismal and organismal levels would lead to a better understanding of the mechanisms of toxic effects. The capacity to relate such information to different biological levels would improve the ability to predict the effects of OPs on ecosystems, especially if linked to parameters that describe population dynamics. In this study, the biochemical, metabolic, and behavioural responses of D. magna after pulse exposure to a sublethal level of paraoxon-methyl, the active metabolite of parathion-methyl, were assessed. The aims were (i) to record changes in ChE, filtration, and swimming activities, (ii) to compare the sensitivity of these activities and their recovery potential, and (iii) to evaluate the implications of the changes on physiological endpoints, namely, nitrogen metabolism from this study and body size from an earlier study (see Table 1; Duquesne, 2006).
Section snippets
Chemicals
The choice of paraoxon-methyl instead of parathion-methyl was based on various criteria. It avoids to quantify, in the daphnids, the exact doses and rates of metabolization of parathion-methyl and enables to assume a direct correlation between exposure concentrations and effective doses. Furthermore, the metabolite is less lipophilic than the parent compound (log Kow: 0.98–1.33 versus 2.75–2.86), and thus the lower sorption on containers facilitates the comparison of results of different tests.
Cholinesterase activity
Exposure of D. magna to paraoxon-methyl inhibited cholinesterase (ChE) activity in a concentration-dependant manner (Fig. 2). After 24 h of exposure, ChE activity was reduced by 70% or more at concentrations equal to or greater (≥) than 1.0 μg L−1 compared with the control values (data from Duquesne, 2006). New data for the subsequent 24 h recovery phase, which occurred directly after the 24 h pulse exposure, showed that the enzyme activity had recovered significantly at the end of this period.
Responses of various parameters after the exposure and recovery phases
This study investigated the effects of a sublethal pulse of paraoxon-methyl on biochemical, metabolic, and behavioural parameters in D. magna. Although these parameters responded to various pathways of different complexities, they all showed significant and simultaneous responses. These effects were all transient and, after a subsequent 24 h period in clean medium, the values had recovered either partly or completely to control levels.
ChE activity varied in a concentration-dependant manner and
Conclusion
The threshold levels for the effects of exposure to pesticides vary depending on the endpoints considered. Despite a high potential for the affected parameters to recover, the effects of pesticides can propagate through biological systems and possibly induce long-term effects at higher levels of biological organisation. It is important to understand such mechanisms to clarify the significance of effects exerted on various levels. Such knowledge is highly relevant for the assessment and
Acknowledgments
The authors acknowledge the scientific support from M. Liess, S. Reynaldi and K. Jung, as well as the technical support from I. Raenker, S. Trogisch and H.A. Dau and the financial support of the UFZ.
References (55)
- et al.
Analysis of the swimming velocity of cadmium-stressed Daphnia magna
Aquat. Toxicol.
(1999) - et al.
Biochemical factors contributing to response variation among resistant and sensitive clones of Daphnia magna Straus exposed to ethyl parathion
Ecotoxicol. Environ. Saf.
(2001) - et al.
Role of B-esterases in assessing toxicity of organophosphorus (chlorpyrifos, malathion) and carbamate (carbofuran) pesticides to Daphnia magna
Aquat. Toxicol.
(2004) - et al.
Sublethal impact of short term exposure to the organophosphate pesticide azamethiphos in the marine mollusc Mytilus edulis
Mar. Pollut. Bull.
(2007) - et al.
A comparison of feeding efficiency and swimming ability of Daphnia magna exposed to cypermethrin
Aquat. Toxicol.
(2005) - et al.
Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: II. Organism and population-level endpoints
Mar. Environ. Res.
(2005) - et al.
Toxicity of sodium molybdate and sodium dichromate to Daphnia magna Straus evaluated in acute, chronic, and acetylcholinesterase inhibition tests
Ecotoxicol. Environ. Saf.
(2000) Effects of an organophosphate on Daphnia magna, at suborganismal and organismal levels: implications for population dynamics
Ecotoxicol. Environ. Saf.
(2006)- et al.
From biomarkers to population responses in Nereis diversicolor: assessment of stress in estuarine ecosystems
Ecotoxicol. Environ. Saf.
(2007) - et al.
Trace nutrient deficiency in Daphnia magna cultured in standard medium for toxicity testing. Effects of the optimization of culture conditions on life history parameters of Daphnia magna
Water Res.
(1990)
A new and rapid colorimetric activity
Biochem. Pharmacol
Effect of the insecticide methylparathion on filtration and ingestion rates of Brachionus calyciflorus and Daphnia rnagna
Sci. Total Environ.
Effect of sublethal concentrations of pesticides on the feeding behavior of Daphnia magna
Ecotoxicol. Environ. Saf.
Different susceptibility of two aquatic vertebrates (Oncorhynchus mykiss and Bufo arenarum) to azinphos methyl and carbaryl
Comp. Biochem. Physiol. C: Toxicol. Pharmacol.
Photochemical activities of a particle fraction P1 obtained from green-alga Chlorella Fusca
Biochem. Biophys. Res. Commun.
Inhibition of acetylcholinesterase activity as effect criterion in acute tests with juvenile Daphnia magna
Chemosphere
Free amino acids as a biochemical indicator of stress in the estuarine bivalve Macoma balthica
Sci. Total Environ.
Invertebrate biomarkers: links to toxicosis that predict population decline
Ecotoxicol. Environ. Saf.
Alterations of physiological energetics, growth and reproduction of Daphnia magna under toxicant stress
Aquat. Toxicol.
Contaminant-stimulated reactive oxygen species production and oxidative damage in aquatic organisms
Mar. Pollut. Bull.
Protein measurement with the Folin Phenol Reagent
J. Biol. Chem.
Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: I. Biochemical endpoints
Mar. Environ. Res.
Understanding the toxic actions of organophosphates
Physiological responses of Macoma balthica to copper pollution in the Baltic
Oceanol. Acta
The role of ecotoxicity in organophosphorous nerve agents central poisoning
Trends Pharmacol. Sci.
Altered cholinesterase and monooxygenase levels in Daphnia magna and Chironomus riparius exposed to environmental pollutants
Ecotoxicol. Environ. Saf.
Evaluation of the swimming activity of Daphnia magna by image analysis after administration of sublethal cadmium concentrations
Compar. Biochem. Physiol. A Mol. Integr. Physiol.
Cited by (40)
Ecotoxicology of microplastics in Daphnia: A review focusing on microplastic properties and multiscale attributes of Daphnia
2023, Ecotoxicology and Environmental SafetyPlanarian behavioural endpoints in ecotoxicology: A case study evaluating mercury and salinity effects
2021, Environmental Toxicology and PharmacologySublethal effects of DBE-DBCH diastereomers on physiology, behavior, and gene expression of Daphnia magna
2021, Environmental PollutionStandard and biochemical toxicological effects of zinc pyrithione in Daphnia magna and Daphnia longispina
2020, Environmental Toxicology and PharmacologyCitation Excerpt :Locomotion is a feature usually compromised by a series of toxicants but seems to be rather unspecific. In fact, changes in mobility of living organisms have been associated to various environmental factors, such as light, water temperature, food presence and predators (Hamza and Ruggiu, 2000; Ziarek et al., 2011), but may be also changed by exposure to pesticides (Dodson et al., 1995; Duquesne and Küster, 2010), hormonal drugs (Goto and Hiromi, 2003), cyanobacterial toxins (Ferrão-Filho et al., 2014; Restani and Fonseca, 2014), metals such as cadmium (Wolf et al., 1998), among others. In the present study, swimming traits of exposed organisms were not altered following a clear dose-response pattern, and the changes were diffuse in relation to the exposure parameters and cycles, with some moments of excitation (increase in distance and time) or inhibition (decrease in distance and time).
Physiological endpoints in daphnid acute toxicity tests
2020, Science of the Total Environment