The effects of chemical warfare agent Clark I on the life histories and stable isotopes composition of Daphnia magna

Chemical warfare agents (CWA) dumped worldwide in all types of aquatic reservoirs pose a potentialenvironmental hazard. Leakage of CWAs from eroding containers at dumping sites had been observed,and their presence in the tissues of aquatic animals was confirmed. However, the ecological effects ofCWA have not yet been studied. In standardized laboratory bioassays, we tested if sublethal concen-tration of Clark I, an arsenic based CWA, can affect life histories (somatic growth rate, fecundity, size atmaturity), population growth rate and stable isotope signatures of a keystone crustacean grazerDaphniamagna. We found that the life histories andfitness of daphnids reared in the presence of Clark I differedfrom those reared in Clark-free conditions. The effects were observed when Clark I concentrations wereno less than 5mgL1. With increasing concentrations of the tested CWA, all of the tested parametersdecreased linearly. Thefinding indicates that even sublethal concentrations of Clark I can affect crus-tacean populations, which should be taken into account when assessing the environmental risks of thisparticular CWA. We found intraspecific diversity in susceptibility to Clark I, with some clones beingsignificantly less vulnerable than others. We also found that in the presence of Clark I, the ratio of heavyand light isotopes of nitrogen in the bodies of daphnids was affectededaphnids exhibitedd15Nenrichment with increasing concentrations of this CWA. The isotopic composition of carbon was notaffected by the presence of Clark I. The nitrogen isotopic signature may be used as an indicator of stress inzooplankton exposed to the presence of toxic xenobiotics.