COMPARATIVE ACUTE AND CHRONIC TOXICITY OF DIETHYLENETRIAMINE PENTAACETIC ACID (DTPA) AND FERRIC-COMPLEXED DTPA TO DAPHNIA-CARINATA

The acute and chronic toxicity of diethylenetriamine pentaacetic acid (DTPA) and ferric complexed DTPA (Fe[III]DTPA) to Daphnia carinata wer e compared, while the effects of DTPA exposure prior to and/or during Ist brood embryogenesis were also assessed. For chronic exposures, dap hnids were exposed to DTPA at high or low food levels, or to Fe(III)-D TPA at high food level until the 6th reproductive instar. The 48 h LC( 50)s of DTPA and Fe(III)-DTPA to D. carinata were 245 mg/L and >1,000 mg/L, respectively Chronic exposure to IO mg/L DTPA resulted in a sign ificant reduction in all individual brood sizes, while it increased th e age at each reproductive instar. Ten mg/L DTPA also significantly de creased the cumulative number of offspring per adult at high and low f ood level from 161.3 +/- 14.6 to 11.3 +/- 4.9 offspring, and 56.4 +/- 1.8 to 0 +/- 0 offspring, respectively while a similar effect was obse rved for the number of offspring per adult per day. Both the 3rd and 5 th brood sizes were also significantly reduced at 1 mg/L DTPA, but onl y at high food level, from 39.0 +/- 2.9 to 27.6 +/- 3.8 offspring, and 49.3 +/- 5.0 to 39.9 +/- 4.2 offspring, respectively. Chronic exposur e to Fe(III)-DTPA had little effect on D. carinata, but there was a si gnificant negative relationship between Fe(III)-DTPA and the number of offspring per adult per day (y = -0.024x + 14.048, r(2) = 0.20, n = 2 6, P < 0.02). This was due to a 25% reduction in reproduction at 134 m g/L Fe(III)-DTPA, the highest test concentration, compared to controls . The no-observed-effect concentrations (NOEC) and lowest-observed-eff ect concentrations (LOEC) for DTPA and Fe(III)-DTPA following chronic exposure to D. carinata were 1.0 and 10 mg/L, and 67 and 134 mg/L, res pectively, although the possibility of effects occurring below 10 mg/L DTPA could not be discounted. Exposure to DTPA prior to Ist brood emb ryogenesis significantly decreased the Ist brood size but did not affe ct the 2nd brood size, while exposure during Ist brood embryogenesis s ignificantly decreased the 2nd brood size, but did not affect the Ist brood size, indicating the reproductive impairment was due to maternal ly-mediated factors and not direct toxicity to the eggs. The decrease in DTPA toxicity when complexed with Fe(III) was attributed to prefere ntial binding with that metal, thereby limiting any further chelating ability. Concentrations of DTPA in receiving waters are unlikely to be toxic to D. carinata.