Avoidance behaviour of Enchytraeus albidus (Oligochaeta) after exposure to AgNPs and AgNO3 at constant and fluctuating temperature

We conducted avoidance tests at fixed (20 °C) and fluctuating temperature (15/25 °C) for 2 and 7 days to assess the effects of temperature regime and duration of exposure on the avoidance of Enchytraeus albidus towards silver nitrate (AgNO3) and silver nanoparticles (AgNPs). The metal contents of the worms that avoided both toxicants were measured in order to find out whether these worms explored both soil environments before displaying the observed avoidance behaviour. Successful avoidance of AgNO3 was found under both temperature regimes at day 2 (10% < net response< 90%). At day 7, the net avoidance response had decreased to between 20 and 40% at 15/25 °C, whereas at constant temperature (20ᵒC) the worms did not avoid AgNO3. With regard to AgNPs, at day 2 the avoidance response was greater at constant (≥60% net response) than fluctuating temperature (≤40% net response). At day 7, under fluctuating temperature a slight increase in avoidance was observed while it was the opposite at constant temperature. In general, the response at day 7 was similar between the two temperature regimes. For both toxicants, we found that longer exposure than 48 h may better reveal the range of avoidance behaviour that occur under more environmentally realistic conditions. Ag tissue contents in the worms which had shown avoidance behaviour revealed that these worms had explored the contaminated soil compartments but the overall results indicate that metal body burdens would be a poor predictor of the avoidance behaviour of E. albidus.