# Change in activity in Baltic clam (Macoma balthica) exposed to elevated sulphate concentrations

## TL;DR

This study explores how elevated sulphate concentrations affect the activity of Baltic clams, suggesting that behavioral endpoints can be useful in ecotoxicology.

## Contribution

The study introduces a low-cost methodology for using activity as a chronic toxicity endpoint in bivalves under sulphate exposure.

## Key findings

- Activity inhibition in Baltic clam adults decreased over time with sulphate exposure.
- Juvenile Baltic clams had a survival LC10 of 9001 mg/L sulphate.
- Activity EC10s in adults were lower than wet mass EC10s, indicating higher sensitivity.

## Abstract

Behavioral endpoints have been increasingly used in ecotoxicology for their relevance to individual fitness and ecological effects. However, due to the lack of standard experimental protocols, behavioral endpoints are mostly excluded when deriving environmental quality guidelines. To increase reliability and comparability, behavioral endpoints need to be developed alongside standard endpoints in experiments incorporating elements of standard protocols. In this study, we explored a low-cost methodology to examine the use of activity as a chronic endpoint in a bivalve species in sulphate toxicity tests, following principles of the standard protocol. Adults and juveniles of Baltic clam (Macoma balthica) were exposed to sodium sulphate separately. The adult bivalves were individually inspected for their activity at frequent intervals. Activity was at first inhibited, but the extent of activity inhibition decreased and activity EC10 (10% effective concentration) increased as the exposure continued. In M. balthica juveniles, LC10 based on survival was 9001 mg/L sulphate. In M. balthica adults, activity EC10s (1713 − 3176 mg/L) were consistently lower than wet mass EC10 (5511 mg/L). Siphonal autotomy in M. balthica was observed at similar sulphate levels as the activity-based chronic EC10s. We found that the sensitivity of behavioral endpoints in major ion exposures depended on the duration of exposure and, consequently, they need to be evaluated in a case-by-case scenario in the regulatory ecotoxicological context.

The online version contains supplementary material available at 10.1007/s10646-025-02977-7.