Multigenerational exposure of Folsomia candida to silver: Effect of different contamination scenarios (continuous versus pulsed and recovery).

ABSTRACT

Effects of pollutants are mostly assessed using standard testing procedures, which cover a fraction of the animals' life cycle. Although, in nature species are exposed during multiple generations of sub-lethal doses of persistent chemicals. In the present study, we focused on the multigenerational (MG) effects of silver in Folsomia candida during 6 generations using the EC50 for reproduction as exposure concentration. We tested 9 different exposure scenarios, going from continuous 6 generations Ag exposure over pulse exposure (i.e. one generation clean, next contaminated, next clean etc.) to gradually increasing the number of exposure generations, with a final transfer to clean media. The biological endpoints assessed included survival, reproduction and size, with reproduction being the most sensitive. The biological response depended on the specific MG scenario, e.g. the 6 Ag MG caused a decreased number of juveniles from F4, whereas the pulse exposure experienced an increase in reproductive output when in clean soil. It is uncertain whether Ag causes transgenerational effects, but the reproduction levels in both pulse exposures are lower than in continuous control over the 6 generations which could be due to transference of Ag by the maternal generation. Overall, population size distribution seemed to indicate a delay in time for egg laying, with close relationship between adult survival, organisms size and reproduction output. Size monitoring allowed significant added interpretation possibilities and we strongly recommend the addition of this endpoint to the standard guideline. The smaller observed size range can have implications in terms of adaptation potential, carrying associated increased risk.