Antioxidant status in relation to age,condition, reproductive performance and pollution in three passerine species

Oxidative stress has been suggested as a mediator in life‐history trade‐off. By spending more resources on for example reproduction an organism might sacrifice its antioxidant defence. So far, most conclusions on trade‐offs between life‐history traits and oxidative stress have been drawn from laboratory studies using a few model species and there is a need for studies conducted in natural settings. We investigated associations between markers for antioxidant status (antioxidant enzyme activities and antioxidant levels), body condition, age and reproduction in three species of wild‐living passerines. The impact from an anthropogenic stressor (metal pollution) was also assessed. The three bird species showed interspecific variation in their SOD and CAT activities, indicating different pathways to eliminate radicals. The age of females affected both antioxidant status and the breeding performance, indicating the importance of age as a factor in life‐history studies. Old birds had lower levels of antioxidants/antioxidant enzyme activities and they produced larger broods/more successful broods, though the latter might be confounded by surviving females having increased fitness. Metal exposure had a negative impact on breeding, and improved breeding outcome was also associated with increased antioxidant defence, but metal exposure was not directly related to the oxidative status of birds, emphasizing that additional stressors might independently affect the same traits. Our results highlight that caution has to be taken when generalizing and extrapolating results to even closely related species. The results support the idea that there is a cost of reproduction, in terms of increased resources spent on antioxidant defence, though this should be confirmed with experimental studies.     

Long-term recovery of macroinvertebrate biota in grossly polluted streams: Re-colonisation as a constraint to ecological quality

To meet targets imposed by the European Water Framework Directive (2000/60/EC) it is vital that measures to improve the status of rivers are both effective and economically viable. Achievement of such aims needs robust understanding of biological responses to changes in water quality vis-à-vis mechanisms of and constraints to the colonization of previously polluted sites. This study therefore examined the long-term chemical and biological changes in historically polluted rivers to elucidate the responses of macroinvertebrate biota to improvements in chemical water quality. For three historically polluted sites in the English Midlands, data from surveys over a period of ca. 50 years were analysed. Ammonia (NH₃) and 5-day biochemical oxygen demand (BOD₅) were used as chemical water quality indicators. Variations in the ecological recovery of the study sites were assessed using an average pollution sensitivity score (Average Score Per Taxon) and the number of taxa present (usually to family level) present in hand-net samples. Ecological recovery varied widely and was influenced by the intensity and spatial extent of the pollution and the proximity of available sources of potential colonisers. At the site most isolated from potential sources of colonizing taxa, no clean-water macroinvertebrate taxa were recorded 30 years after the major sources of pollution ceased. Where clean-water colonisers were more readily available, significant improvements in ecological quality followed within 2–5 years of the improvements in chemical quality. Macroinvertebrate communities and hence monitoring data may thus be indicative of long past conditions or of biological isolation rather than contemporaneous chemical conditions. Combined chemical and biological data were used to explore a generic model for predicting recovery rates and success. Neither BOD₅ nor NH₃ were found to provide a consistent and meaningful prediction of either average pollution tolerance of macroinvertebrate taxa or of the number of taxa present. Long-term relationships between macroinvertebrate variables and chemical water quality variables, however, were non-linear, suggesting that water quality thresholds may have to be exceeded before biological recovery can occur. Even when chemical water quality has been improved substantially, the apparent ecological status of macroinvertebrate communities may not reflect reduced pollution levels attained until adequate time to allow for re-colonisation (possibly decades) has elapsed.     

Comparing macroinvertebrate indices to detect organic pollution across Europe: a contribution to the EC Water Framework Directive intercalibration

With the EC Water Framework Directive (WFD) the ecological status of a water body is defined by comparing the observed biological community composition present with near-natural reference conditions. The ecological status is then classified into five quality classes (high, good, moderate, poor and bad). It is of great importance that `good ecological status' has the same meaning within the European Union, since water bodies not measuring up to these standards have to be improved. Therefore, the Ecological Quality Ratios (EQR) at high-good, and good-moderate quality class boundaries will be intercalibrated. Each country has to report physical, chemical, and biological data from two sites at each of these boundaries and since most data exist for benthic macroinvertebrates, this quality element will be of great importance in the intercalibration process. The aim of this study was therefore to compare the results of different benthic macroinvertebrate metrics used to assess the impact of organic pollution (including eutrophication) (one of the major human impacts on European streams). A selection of the data sampled in the AQEM project was evaluated, where benthic macroinvertebrate- and abiotic data from four countries (Austria, the Czech Republic, Portugal and Sweden) and seven `stream types' were included. An organic pollution (including eutrophication) gradient was defined using Principal Component Analysis and the boundaries for high-good and good-moderate ecological status set by the partners from each country were used to define arbitrary class boundaries. The Average Score Per Taxon (ASPT) was well correlated with the stress gradient in most stream types, whereas the Saprobic Index worked clearly better than ASPT in those countries (Austria and the Czech Republic) where macroinvertebrates are generally identified to lower (species) as opposed to a higher (genus or family) level of identification. Defining harmonised class boundaries is difficult; this process has to consider the natural differences between stream types (e.g. in the reference values of metrics) but has to eliminate different perceptions of ecological quality.     

Skin resistance to oxidative stress induced by resveratrol: From Nrf2 activation to GSH biosynthesis

Skin is particularly exposed to oxidative stress, either from environmental insults such as sunlight or pollution or as a consequence of specific impairments in antioxidant status resulting from pathologies or aging. Traditionally, antioxidant products are exogenously provided to neutralize pro-oxidant species. However, another approach based on stimulation of endogenous antioxidant defense pathways is more original. Resveratrol (RSV) was reported to display such a behavior in various tissues, but data about the mechanisms of action in skin are scarce. We show here that, in primary culture of normal human keratinocytes (NHKs) or in full-thickness reconstructed human skin, RSV activated the Nrf2 pathway at nontoxic doses, from 20 µM up to 100 µM. Among the Nrf2 downstream genes, glutamylcysteinyl ligase and glutathione peroxidase-2 were induced at the mRNA and protein levels. In parallel, a significant increase in glutathione content, assessed by LC/MS analysis, was observed in both models. Nrf2 gene silencing experiments performed in NHKs confirmed that Nrf2 was involved in RSV-induced modulation of cellular antioxidant status, in part by increasing cellular glutathione content. Finally, improvement of endogenous defenses induced in RSV-pretreated reconstructed skin ensured protection against the toxic oxidative effects of cumene hydroperoxide (CHP). In fact after RSV pretreatment, in response to CHP stress, glutathione content did not decrease as in unprotected samples. Cellular alterations at the dermal–epidermal junction were clearly prevented. Together, these complementary experiments demonstrated the beneficial effects of RSV on skin, beyond its direct antioxidant properties, by upregulation of a cutaneous endogenous antioxidant pathway.     

Note: the effect of parasite infection on the innate immune response of European flounder (Platichthys flesus L.) in the southern North Sea

In a field study, infecting European flounder (Platichthys flesus L.) subclinically with different parasite species did not result in any alteration of the innate immune response. Due to the high variability in infection status and the immune parameters measured, no relationships of biological significance were found. The data indicate that copepods, as the most abundant parasites, most probably had no major influence on immune responses measured here. Thus it might be concluded that these parameters were not sensitive to parasite infections occurring under natural conditions. The immune parameters considered here are regarded as promising indicators of chemical contaminant-induced variation in piscine immune responses, which could be implemented in pollution monitoring programmes. Communicated by H. v. Westernhagen, A. Diamant     

Lipid peroxidation and regulation of it in rat blood and liver under the experimental alimentary radionuclide effect

Effect of alimentary radionuclide load (137Cs, 700 Bq for animal per day during 7, 14 and 22 days) on the lipid peroxidation intensity and blood and liver enzymatic and non-enzymatic antioxidant system in the Wistar male-rats was investigated. It was found that considerable change of antioxidant system activity in plasma and erythrocytes of experimental animals was already noticeable on the 7th day of radionuclide load. After 22 days of experiment the reliability of glutathione-dependent antioxidant system in blood was essentially decreased and lipid hydroperoxide content was increased. The increase of lipid peroxidation intensity was also found in the experimental animals liver but at the same time the activities of all studied enzymes of antioxidant system were significantly higher than they were in the control rats.     

Influence of the polyphenolic tannic acid on the toxicity of the insecticide deltametihrin to fish. A comparative study examining both biochemical and cytopathological parameters

Humics and pesticides are present in aquatic environment and the toxicological consequences of their chemical interaction is well studied. However, data concerning the mechanism of the biochemical action of humic-pesticide combinations are scarce, especially in vertebrates. Thus we have chosen to study the in vivo effects of the plant polyphenolic tannic acid and the pyrethroid insecticide deltamethrin [Decis] alone or in combination on hepatic xenobiotic-metabolizing enzyme activities and the associated redox-parameters in carp, as the complex assessment of these systems are regarded to serve as a relevant biomarker of environmental pollution. Stress effects and tissue damage were followed by determination of the plasma glucose level, the activities of plasma transaminases, and by electron microscopy. Tannic acid alone exerted weak prooxidant effect due to its marked antioxidant enzyme inhibitory activity. Deltamethrin, applied in a very low dose, induced oxyradical production in fish via activation of cytochrome P450 isozymes. This effect was promoted by the antioxidant enzyme inhibitory action of tannic acid, when the two chemicals were combined; however, the ultrastructural damage of the hepatocytes was reduced by the common cytoprotective capacity of the phenolic. Numerous humics are known to alter the toxicity of pesticides and their influence depends on their type and concentration. Therefore, our work taken together with other comparative studies may contribute to the assessment of the impact of humics in nature, especially in case of environmental pollution.     

The relationship between biomarkers of oxidative DNA damage, polycyclic aromatic hydrocarbon DNA adducts, antioxidant status and genetic susceptibility following exposure to environmental air pollution in humans

Polycyclic aromatic hydrocarbons (PAHs) appear to be significant contributors to the genotoxicity and carcinogenicity of air pollution present in the urban environment for humans. Populations exposed to environmental air pollution show increased levels of PAH DNA adducts and it has been postulated that another contributing cause of carcinogenicity by environmental air pollution may be the production of reactive oxygen species following oxidative stress leading to oxidative DNA damage. The antioxidant status as well as the genetic profile of an individual should in theory govern the amount of protection afforded against the deleterious effects associated with exposure to environmental air pollution. In this study we investigated the formation of total PAH (bulky) and B[a]P DNA adducts following exposure of individuals to environmental air pollution in three metropolitan cities and the effect on endogenously derived oxidative DNA damage. Furthermore, the influence of antioxidant status (vitamin levels) and genetic susceptibility of individuals with regard to DNA damage was also investigated. There was no significant correlation for individuals between the levels of vitamin A, vitamin E, vitamin C and folate with M₁dG and 8-oxodG adducts as well as M₁dG adducts with total PAH (bulky) or B[a]P DNA adducts. The interesting finding from this study was the significant negative correlation between the level of 8-oxodG adducts and the level of total PAH (bulky) and B[a]P DNA adducts implying that the repair of oxidative DNA damage may be enhanced. This correlation was most significant for those individuals that were non smokers or those unexposed to environmental air pollution. Furthermore the significant inverse correlation between 8-oxodG and B[a]P DNA adducts was confined to individuals carrying the wild type genotype for both the GSTM1 and the GSTT1 gene (separately and interacting). This effect was not observed for individuals carrying the null variant.     

Soil microbial community structure and functionality changes in response to long-term metal and radionuclide pollution

Microbial communities are essential for a healthy soil ecosystem. Metals and radionuclides can exert a persistent pressure on the soil microbial community. However, little is known on the effect of long-term co-contamination of metals and radionuclides on the microbial community structure and functionality. We investigated the impact of historical discharges of the phosphate and nuclear industry on the microbial community in the Grote Nete river basin in Belgium. Eight locations were sampled along a transect to the river edge and one location further in the field. Chemical analysis demonstrated a metal and radionuclide contamination gradient and revealed a distinct clustering of the locations based on all metadata. Moreover, a relation between the chemical parameters and the bacterial community structure was demonstrated. Although no difference in biomass was observed between locations, cultivation-dependent experiments showed that communities from contaminated locations survived better on singular metals than communities from control locations. Furthermore, nitrification, a key soil ecosystem process seemed affected in contaminated locations when combining metadata with microbial profiling. These results indicate that long-term metal and radionuclide pollution impacts the microbial community structure and functionality and provides important fundamental insights into microbial community dynamics in co-metal-radionuclide contaminated sites.     

Influence of technogenic dust pollution on changes in the physiological and biochemical adaptation and radioresistance of pepperweed (Lepidium apetalum Wild.) seedlings

The influence of technogenic dust pollution on changes in the physiological and biochemical characteristics and their heterogeneity (variability) has been studied in Lepidum apetalum seedlings, as has the formation of their radioresistance. In spite of the high antioxidant status of seedlings, a higher level of dust pollution in the habitat of maternal plants does not significantly influence the radioresistance of seedlings when compared to the control group, which is probably a result of the reduced variability of the studied characteristics.     

Phenotypic variability of the pearly heath, Coenonympha arcania L. (Lepidoptera, Satyridae) in natural and anthropogenically transformed habitats in the Middle and South Urals

Analysis of variation of the wing length and eyespots in Coenonympha arcania (Linnaeus, 1761) (Lepidoptera, Satyridae) in the Middle and South Urals showed greater differences between populations from the forest and steppe zones than between populations from natural habitats and those subjected to chemical and radionuclide pollution. Based on small values of the fluctuating asymmetry (FA) index in all the habitats examined, it may be concluded that C. arcania finds favorable environment in both natural and anthropogenically transformed habitats in the Middle and South Urals.     

近20年广西钦州湾有机污染状况变化特征及生态影响

利用1990至2010年长期监测的结果,采用有机污染指数法对钦州湾近20年有机污染程度进行评价,分析其变化趋势并探讨其对海湾环境的潜在生态影响。结果表明近20a钦州湾有机污染指数变化较大,内湾变化范围为-0.55-5.49,外湾的变化范围为-0.44-3.96。20世纪90年代内湾和外湾有机污染物程度均显下降趋势,1999-2003年显上升趋势,2003年以后外湾显平稳波动状态而内湾为显著增加的趋势,近几年内湾有机污染加重到严重污染的程度。径流输入、浮游植物消耗以及水体交换等因子的综合作用是该海湾有机污染变化的主要因素,也是导致内湾和外湾变化差异的主要原因。海湾有机污染的变化导致富营养化的变化,有机污染和富营养化程度的变化并没有与浮游植物生物量的变化显著相关,但内湾近年来急剧加重的有机污染增加了赤潮等生态灾害的风险。内湾有机污染加重也会对水产增养殖等产生影响,需要加大关注和防治。     

Moderate exercise prevents impaired Ca2+ handling in heart of CO-exposed rat: implication for sensitivity to ischemia-reperfusion

Sustained urban carbon monoxide (CO) exposure exacerbates heart vulnerability to ischemia-reperfusion via deleterious effects on the antioxidant status and Ca(2+) homeostasis of cardiomyocytes. The aim of this work was to evaluate whether moderate exercise training prevents these effects. Wistar rats were randomly assigned to a control group and to CO groups, living during 4 wk in simulated urban CO pollution (30-100 parts/million, 12 h/day) with (CO-Ex) or sedentary without exercise (CO-Sed). The exercise procedure began 4 wk before CO exposure and was maintained twice a week in standard filtered air during CO exposure. On one set of rats, myocardial ischemia (30 min) and reperfusion (120 min) were performed on isolated perfused rat hearts. On another set of rats, myocardial antioxidant status and Ca(2+) handling were evaluated following environmental exposure. As a result, exercise training prevented CO-induced myocardial phenotypical changes. Indeed, exercise induced myocardial antioxidant status recovery in CO-exposed rats, which is accompanied by a normalization of sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a expression and then of Ca(2+) handling. Importantly, in CO-exposed rats, the normalization of cardiomyocyte phenotype with moderate exercise was associated with a restored sensitivity of the myocardium to ischemia-reperfusion. Indeed, CO-Ex rats presented a lower infarct size and a significant decrease of reperfusion arrhythmias compared with their sedentary counterparts. To conclude, moderate exercise, by preventing CO-induced Ca(2+) handling and myocardial antioxidant status alterations, reduces heart vulnerability to ischemia-reperfusion.     

Macrozoobenthos communities and biocoenotic assessment of ecological status in relation to degree of human impact in small streams in southwest Germany

One of the major objectives of the VALIMAR project is to determine the ecological significance of various fish biomarker studies as indicators of chronic pollution in small streams in southwest Germany. Results of these fish biomarker investigations were compared to information from complementary studies on the meiobenthos, macrobenthos, and fish community studies to assess the ecological significance of these biomarker investigations. The main objective of this study was to provide biological assessments of the biomarker sites on the basis of the macrozoobenthos communities. Since no validated framework for the assessment of the biological integrity existed in Germany, two multimetric approaches were adapted to the whole stream system by investigating benthos and fish communities of 46 sites of varying degrees of human disturbance. Assessment of the communities was conducted in accordance with the European Community Water Framework Directive. Species distribution of benthos depended upon stream type and pollution status of streams. Biological attributes and bioindices of benthos communities, however, did not correlate with typological parameters like stream size or dominant substrate but correlated better with pollution parameters like conductivity or chloride concentration. Using a set of 18 measures, such as portion of sessile individuals, Rheoindex, oxygen availability index, and portion of pool dwellers, the benthos communities were characterized and evaluated. The composition of the fish communities was mainly determined by stream type, pollution and migration barriers. The influence of chemical parameters could be assessed by developing a“fish chemistry index”, which calculatesthe similarity of the present fish community with the potential natural community, but excludes those species strongly effected by deficits in stream channel morphology. Both fish chemistry index and benthic indices strongly correlated with pollution index parameters, clearly distinguishing between the more polluted Körsch sites and the less pollutedKrähenbach and Aich sites. Most of the single bioindices as well as overall assessment by multimetric indices indicated a gradient of decreasing quality from the reference stream Krähenbach to theslightly polluted Aich and Körsch upstream site (KE, upstream of all sewage treatment plants) and finally to the most polluted Körsch site directlybelow the most upstream sewage treatment plant (KD). According to the Water Framework Directive, the classification of ecological status of the benthos communities ranges from “high” (best of 5 classes) forthe reference stream to “bad” (5th class) for KD. Assessment of the fish community tends to score somewhat worse than the benthos due to deficits in morphological quality of the stream reaches. The benthos assessment and the newlydeveloped “fish chemistry index” correlated well with chemical water quality and hence with biomarkers, whereas ecological status of fish and overall ecological status was also influenced by river morphology. In conclusion all tested assessment methods on biocoenotic level are reliable indicators for the degree of human disturbance on small streams, whereas biomarkers are more suited for risk assessment and the investigation ofcause-effect-relationships.     

Egg yolk carotenoids in relation to habitat and reproductive investment in the great tit Parus major

Maternal allocation of antioxidants to egg yolk has been shown to affect early embryonic development and nestling survival. In environments with high levels of anthropogenic pollution, antioxidants (such as carotenoids) are important to protect the body from elevated oxidative stress. Thus, female allocation of antioxidants to yolk may be traded off against self-maintenance. Here we investigate maternal reproductive investment with respect to yolk carotenoid content and composition in relation to subsequent female condition and carotenoid status in urban and rural great tits Parus major. We found no differences between the urban and rural populations in total yolk carotenoids, egg mass, clutch size, hatching success, or female carotenoid status. Interestingly, however, rural eggs contained more zeaxanthin, a more potent antioxidant than lutein, which suggests that rural embryos have better antioxidant protection than urban embryos. Whether rural females actively transfer more zeaxanthin to the yolk or whether it passively reflects differences in dietary access or uptake needs to be further investigated. This highlights the importance of carotenoid identity and composition in future studies of carotenoid physiology, ecology, and signaling.     

Migration characteristics and forms of 90Sr and 137Cs observed in the bottom sediments of certain lacustrine ecosystems on the East Urals Radioactive Trace

The research findings summarized in the paper include data on the radioecological conditions in two lakes (Large Ighish and Small Ighish) located on the East Urals Radioactive Trace. The focus of the study was on the chemical composition of water and bottom sediments, as well as on the specific features of 90Sr and of 137Cs distribution and the forms in which they occur in silts. Coefficients of radionuclide accumulation in the bottom deposits of the lakes of interest were estimated. A conclusion was drawn about the dependences influencing radionuclide distribution by layers of the lake bottom sediments.     

Estimating transfer parameters in the absence of data

The calculation of transfer of radionuclides from the abiotic to the biotic environment is a well-established practice in radiological assessments. Concentration ratios provide simple means to estimate radionuclide activity in biota, from measured (or estimated) radionuclide concentrations in either a food source or an abiotic component such as soil or water. They are typically reported by element, and data compilations may include information such as soil type (e.g., sand, loam, clay) and species. The data may be for multiple species at a single location, single species at multiple locations, or represent compilations from multiple sources. Recently published guidance suggests that estimates are best made using data from the same ecosystem. This paper examines this recent guidance, in the context of using measured data from within a single ecosystem and comparing results to more generic values. Results suggest that generic values may be an adequate substitute for site-specific information. It illustrates how ionic potential may be used as an alternative to group chemical properties in estimating transfer factors. Lastly, limited evidence is found to support the concept of allometric scaling functions for elemental concentrations in plants.     

Ascorbate and glutathione contents in duckweed,Lemna minor,as biomarkers of the stress generated by copper,folpet and diuron

Glutathione and ascorbate are essential components of the general antioxidative strategy to overcome oxidative stress due to environmental constraints such as pollution. The variation of glutathione and ascorbate contents in duckweed (Lemna minor) was investigated after a 48 h exposure to copper, diuron and folpet under laboratory conditions in order to determine whether changes in their level could serve as suitable and early biomarkers of pollution. One could observe that diuron and folpet caused the glutathione level to increase, its redox status remaining unchanged, while copper led to a depletion of this antioxidant and to an increase in its oxidation rate. When duckweed was contaminated by folpet and the metal, an increase of the ascorbate pool size occurred from concentrations as low as 1 mg l^?1 and 50 μg l^?1 respectively. While the ascorbate pool became more oxidized because of exposure to copper concentrations ≤ 200 μg l^?1, folpet caused an increase in its reduction rate. Diuron was responsible for depletion of ascorbate, the redox status of which remained unchanged. Because it is an adaptation to stress and a defence process, the increase in the antioxidant pool size was proposed as a biomarker of exposure to an unsafe environment. Since depletion of antioxidant and an increase in its oxidation rate weakened cellular defences and indicated a precarious state, they could constitute early indicators of toxicity. So they were proposed as potential biomarkers of toxicity. It was concluded that the antioxidant content in duckweed might serve as a useful biomarker for monitoring water quality.     

Biological evaluation of running waters in Korea, with special reference to bioassessment using the PFU system

A total of six stations in the Han River system were selected for establishing polyurethane foam units (PFUs) to collect protozoans, including phytomastigophorans, zoomastigophorans, amoebas and ciliates, in July 1993. In the bioassessment of microbial communities using the PFUs, the number of species decreased as pollution intensity increased. The diversity index values calculated at the main stations generally agreed with the pollution status of the stations. Anyang-Chon (Chon means stream) showed the lowest diversity value (1.89), and all stations, except Masok and Anyang-Chon, showed diversity index values ranging from 3.15 to 3.93. The highest heterotrophic index (HI) value was detected in Anyang-Chon followed by Masok-Chon. The number of species at the main stations reached a maximum on day 11 of being exposed to PFUs. The results of _eq, G and T_90% all suggest that bioassessments using the PFU system were well matched with pollution status of the water. All microbial variables were significantly correlated with comprehensive chemical pollution indices, P_a and P_b , with correlation coefficients ranging from r =0.87 to r=0.96. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ascorbate and glutathione contents in duckweed, Lemna minor, as biomarkers of the stress generated by copper, folpet and diuron

Glutathione and ascorbate are essential components of the general antioxidative strategy to overcome oxidative stress due to environmental constraints such as pollution. The variation of glutathione and ascorbate contents in duckweed (Lemna minor) was investigated after a 48 h exposure to copper, diuron and folpet under laboratory conditions in order to determine whether changes in their level could serve as suitable and early biomarkers of pollution. One could observe that diuron and folpet caused the glutathione level to increase, its redox status remaining unchanged, while copper led to a depletion of this antioxidant and to an increase in its oxidation rate. When duckweed was contaminated by folpet and the metal, an increase of the ascorbate pool size occurred from concentrations as low as 1 mg l^-1 and 50 μg l^-1 respectively. While the ascorbate pool became more oxidized because of exposure to copper concentrations ≤ 200 μg l^-1, folpet caused an increase in its reduction rate. Diuron was responsible for depletion of ascorbate, the redox status of which remained unchanged. Because it is an adaptation to stress and a defence process, the increase in the antioxidant pool size was proposed as a biomarker of exposure to an unsafe environment. Since depletion of antioxidant and an increase in its oxidation rate weakened cellular defences and indicated a precarious state, they could constitute early indicators of toxicity. So they were proposed as potential biomarkers of toxicity. It was concluded that the antioxidant content in duckweed might serve as a useful biomarker for monitoring water quality.