Stress responses of Eisenia andrei and Enchytraeus doerjesi (Oligochaeta) to combined effects of temperature and metal contamination

[摘要] ENGLISH ABSTRACT: The terrestrial Oligochaete species Eisenia andrei and Enchytraeus doerjesi wereexposed to different concentration series of Cd and Zn, both separately and inmixtures for 28 days in artificial OECD soil at 15, 20 and 25°C. At the end of the fourweek exposure period, survival and reproduction were assessed in E. doerjesi andsurvival, reproduction, biomass change, metal uptake and biomarker responses (MTTand comet assays) in E. andrei.Survival results for both E. andrei and E. doerjesi indicated that the lethality of Cdincreased at higher temperatures, whereas the opposite was observed for Zn.Cadmium LC50 values were the highest at 15°C and the lowest at 25°C. In the Zn exposures LC50 increased with increasing temperature. Mixture results in both testorganisms indicated that mixtures were less lethal than the metals separately. Effectsof mixtures on survival, nonetheless, increased with increasing temperature.In the Cd experiment, reproduction in E. andrei was only recorded in the controltreatments at the three temperatures investigated. However, the deleterious effect ofZn on the reproduction of both E. andrei and E. doerjesi decreased with increasingtemperature and Zn EC50 for reproduction increased with increasing temperature.Results for exposures to mixtures indicated in both test organisms that the interactionbetween Cd and Zn were antagonistic. In both E. andrei and E. doerjesi, the effect ofmixture exposures on reproduction decreased with increasing temperatures. Thehighest mixture EC50 values for reproduction were found at higher temperature.In E. doerjesi (using reproduction results in MixToxModules) Cd and Zn interactionswere dose level dependent at the three temperatures investigated. Antagonism wasthe predominant interaction at lower mixture concentrations whereas synergismoccurred at mixture concentrations equal to or higher than the mixtures' EC50 values.Biomass loss increased with increasing temperature in the Cd exposures (p 9 0.05)but not in the Zn exposures in E. andrei. In this species mixture results indicated antagonistic interactions between Cd and Zn at all temperatures investigated. Thedeleterious effect of mixtures on the biomass of E. andrei increased with increasingtemperature.When Cd and Zn interactions were further investigated in E. andrei (using biomassresults in MixToxModules) it was found that they were dose level dependent at thethree temperatures investigated. Antagonism was the predominant interaction at lowermixture concentrations whereas synergism occurred at mixture concentrations higherthan the mixtures EC50 values.The assessment of metal uptake in E. andrei revealed a temperature dependent Cduptake with higher Cd body burdens occurring at higher exposure concentrations andtemperatures (p ≤ 0.05). In the case of Zn, although uptake was lower at highertemperature, there was no statistical difference in uptake between exposureconcentrations and between temperatures. Mixture results however indicated that inmixture exposures less Cd was accumulated by E. andrei than in single Cd exposures(p ≤ 0.05). Inversely, in mixture exposures more Zn was accumulated by E. andreithan in single Zn exposures (p ≤ 0.05).Biomarker studies revealed that Cd and Zn were both cytotoxic and genotoxic whetherin single or mixture exposures. Factorial ANOVA analyses of the effects oftemperature and metals on the reduction of MTT by E. andrei indicated thattemperature rather than the metals was the most important factor controllingmitochondrial activity (p < 0.001). In both Cd and Zn exposures significant deleteriousmetal effects on mitochondrial processes were found to increase with temperature (p ≤0.01). Mixture exposures indicated decreasing cytotoxicity with increasing temperature(p ≤ 0.05) and possible antagonism between Cd and Zn at cellular level.Results of the comet assay showed that the genotoxic profile of Cd was the oppositeof the genotoxic profile of Zn. Cd was less genotoxic at lower temperature andincreasingly deleterious at higher temperature while Zn was more genotoxic at lowerthan higher temperature (p ≤ 0.05). The results of mixture exposures indicated decreasing mixture genotoxicity with increasing temperature and suggested that theinteractions between Cd and Zn at molecular level were probably antagonistic.

[发布机构] Stellenbosch University