Investigating mechanisms of diethylenetriamine pentaacetic acid toxicity to the cladoceran, Daphnia carinata
Van Dam, R.A.; Barry, M.J.; Ahokas, J.T.; Holdway, D.A.
Aquatic Toxicology 46(3-4): 191-210
ISSN/ISBN: 0166-445X DOI: 10.1016/s0166-445x(98)00130-1
A study was carried out to determine if the well-documented diethylenetriamine pentaacetic acid (DTPA)-induced reproductive impairment in the cladoceran, Daphnia carinata, could be attributed to chelation, and subsequent limitation of one or any of the four important trace metals, iron (Fe), copper (Cu), zinc (Zn) and manganese (Mn). Daphnids were exposed to a range of DTPA concentrations at one, two and four times normal Fe, Zn and Mn concentrations, and one, two and three times the normal Cu concentration, in a series of four, three-brood reproductive experiments. Increasing the Fe concentration to 1280 mug/l had no effect on the reproductive impairment after three broods of offspring. However, fourth brood was also monitored in the experiment, and some recovery in reproduction was observed at both 5 and 10 mg/l DTPA and 1280 mug/l Fe. Speciation modelling indicated this was possibly due to an increase in the amount of available Fe, as Fe(OH)2.7Cl0.3. Increasing the Cu concentration to 75 mug/l (nominal) had no effect on the DTPA-induced reproductive impairment. Speciation modelling indicated that even at 75 mug/l Cu, all Cu was bound to DTPA. Increasing the Zn concentration to 100 mug/l (nominal) resulted in a 50-60% recovery in daphnid reproduction at 10 mg/l DTPA. However, speciation modelling indicated that, at 100 mug/l Zn, all Zn was still bound to DTPA. Increasing the Mn concentration to 847 mug/l resulted in a 60-70% recovery in daphnid reproduction at 10 mg/l DTPA, with speciation modelling indicating that the partial reproductive recovery was associated with an increase in available Mn, in the form of Mn-EDTA. The results of this study suggest that the DTPA-induced reproductive impairment observed in D. carinata is due to a large extent to the chelation of Mn and possibly Zn, while the chelation of Fe may also be of importance. The lowest-observed-effect concentration and no-observed-effect concentration of DTPA were 5 and 1 mg/l, respectively,based on reproduction.