Effects of polycyclic aromatic compounds on the drought tolerance of Folsomia fimetaria (collembola, isotomidae)

Drought tolerance (survival at 98.2% relative humidity and 20 degreesC) was investigated for adult individuals of the springtail Folsomia fimetaria af ter three weeks of exposure to different polycyclic aromatic compounds (PAC s). Seven PACs were investigated (acridine, dibenzofuran, carbazole, fluore ne, dibenzothiophene, fluoranthene, and pyrene), with each substance used a t several exposure concentrations. Sublethal concentrations of dibenzothiop hene, fluorene, fluoranthene, and pyrene caused a dose-related decrease in drought tolerance in exposed adults, whereas no such relationship was found for acridine, dibenzofuran, and carbazole. The organisms used in the droug ht tolerance study were taken directly from standard ecotoxicity tests that had just been completed, hence the concentrations causing subsequent effec ts on drought tolerance and those affecting survival and reproduction in th e ecotoxicity tests could be compared. Some of the tested substances signif icantly reduced the drought tolerance of F. fimetaria at concentrations tha t had little effect on survival, indicating a synergistic effect of the two stressors. However, drought tolerance was affected at concentrations below the threshold value for toxicity in standard tests (no-observed-effect con centration for reproduction) only for dibenzothiophene. In the field, soil organisms exposed to contaminants also face multiple environmental stressor s such as drought and cold. Because the reduced drought tolerance is a side effect of chemical exposure, such effects should be considered when extrap olating from laboratory to field conditions.