Modeling responses of Daphnia magna to pesticide pulse exposure under varying food conditions: intrinsic versus apparent sensitivity
Pieters, B. J., Jager, T., Kraak, M. H. S. and Admiraal, W. 2006.
Modeling responses of Daphnia magna to pesticide pulse exposure under varying food conditions: intrinsic versus apparent sensitivity.
Ectoxicology, 15: 601 - 608
Abstract
Recent studies showed that limiting food conditions resulted in either
increased or decreased sensitivity of Daphnia magna to toxicants. It
remained unclear whether these contrasting food-dependent alterations
in toxicity resulted from differences in intrinsic sensitivity of the
daphnids or from changes in toxicokinetics and resource allocation. It
is hypothesized here that, if food level only affects accumulation
kinetics and resource allocation, then the intrinsic sensitivity to
this toxicant should be the same for all food regimes. This hypothesis
was investigated using the DEBtox model, which is based on the theory
of Dynamic Energy Budgets. We examined results of two recently
conducted life-cycle studies on the combined effects of food level and
a pulsed exposure to the pyrethroid insecticide fenvalerate (FV) on
D. magna. The model described the effects of the time-varying exposure
well, and indicated that when the animals did not die from exposure to
FV, full reversibility of toxic effects was possible, allowing a
complete recovery. Results revealed furthermore that the data from
both studies could be described by the same NECs for survival and
assimilation, killing rate and tolerance concentration (132 (49.2 228)
106 ug/L, 0 (0 1.18 105) ug/L, 74.4 (55.6 96.4)
L (ug d) 1 and 5.39 (2.72 18.5) 103 ug/L, respectively). It
is therefore concluded that food-dependent FV toxicity can be
explained by altered toxicokinetics and resource allocation, but not
by changes in the intrinsic sensitivity of the daphnids. This study
implies that the effect of pesticide application in the field depends
on the trophic state of the receiving water body, but also that full
recovery of survivors is possible after FV application.