The effects of pyridine hydrochloride on sublethal behavioural endpoints in the common shore crab, Carcinus maenas.

Pyridine is a by-product of several industrial processes and is traditionally extracted from coal tar. In October 2021, a mass stranding of dead, twitching and moribund crustaceans, including edible crabs and lobsters, were observed off the northeast coast of England leading to speculation that pyridine released from dredging was the causal agent. This led to campaign groups asking for a cessation of dredging activity in the Tees estuary until the matter had been resolved. Over the past few years, considerable debate and scepticism have remained among the UK press and the public regarding the potential role of pyridine in this event. To determine the effects of pyridine on juvenile common shore crabs (Carcinus maenus) we conducted a four-day static renewal exposure experiment with the nominal concentrations 1, 10, 100 and 1000 µg/L pyridine hydrochloride. Mortality was recorded and novel activity behaviours (Mean Pixel Difference (MSD)) measured using a Zantiks LT machine after 2 h, 24 h, 48 h, 72 h and 96 h. Concentrations were chosen as below those reported to be lethal but represent some environmentally relevant concentrations recorded in the area over the past decade. No mortality was recorded following four-day exposure at concentrations up to 1 mg/L. There was no significant effect of pyridine exposure on the distance travelled by the juvenile crabs during the experiment. Pyridine did not significantly affect the activity of the crabs, as recorded by the MSD analysis. However, there was an interaction between light and exposure where individuals in the highest exposure concentration were significantly more active during light phases of the experiment. No obvious twitching or erratic limb movement was observed over the course of the experiment. This research highlights the minimal effects that pyridine, has on crab movements and activity at environmentally relevant concentrations. This research supports the opinion that pyridine was an unlikely casual factor in the mass mortality event in crustaceans in 2021. Furthermore, we highlight the promising use of MSD for subtle behavioural movement analysis in ecotoxicology.