Threshold concentrations of the road salt for adverse effects on females and resting eggs of cladoceran Moina macrocopa

The salinization of freshwaters due to the use of deicing road salts is a serious anthropogenic threat. We investigated the effects of the road deicer, which is mostly composed (ca. 70%) of NaCl, on the life cycle parameters of the cladoceran Moina macrocopa in acute and chronic toxicity tests and on the hatching success of resting eggs exposed to sediments contaminated with the road salt. The negative effects of the road salt on survival and life cycle parameters of animals were observed at concentrations above 5 g L-1. The 6-month exposure of resting eggs to contaminated sediments had a consistent but relatively weak effect on the postexposure hatching of resting eggs. Experiments demonstrated that the concentration of the deicer in the top water layer in the water-sediment systems is more important for the hatching success of resting eggs than the salt content in the sediment. Only 2.2 +/- 1.9% of resting eggs hatched when the deicer content in the top water layer was equal to 12 g L-1. Lethal effects on hatchlings were observed starting from the deicer content in the water equal to 1 g L-1, and 97.0 +/- 0.8% of hatchlings were dead at the deicer content in the water equal to 5 g L-1. Thus, the resilience of resting eggs to the contaminated sediments can ensure the replenishment of the population from the egg bank after the salinity disturbance is diminished but the negative effects of the elevated salt content in surface waters on active population will be manifested at lower salinities.

Automated summary

The road deicer, primarily composed of NaCl, negatively affects survival and life cycle parameters of animals at concentrations above 5 g L-1, as well as the hatching success of resting eggs exposed to contaminated sediments. Resilience of resting eggs to contaminated sediments ensures population replenishment after salinity disturbance diminishes, but negative effects on active population due to elevated salt content in surface waters will be observed at lower salinities.