Environmental levels of atrazine decrease spatial aggregation in the freshwater mussel, Elliptio complanata.

Area of Science:

• Environmental Toxicology
• Ecotoxicology
• Aquatic Ecology

Background:

• Atrazine (ATR) is a widely used herbicide with known estrogen-like effects.
• Xenoestrogens, including ATR, can potentially alter animal behavior.
• Bivalve aggregation is a behavior that may be linked to reproductive strategies.

Purpose of the Study:

• To investigate the effects of short-term exposure to ecologically relevant atrazine concentrations on freshwater mussel aggregation.
• To compare the effects of atrazine with those of estradiol, a known estrogen.

Main Methods:

• Freshwater mussels were exposed to atrazine concentrations ranging from 1.5 to 150 µg/L for 6 and 72 hours.
• The aggregation index (AI), measuring the proportion of mussels in the most crowded tank section, was evaluated.
• Comparisons were made between control groups, estradiol-treated groups, and atrazine-treated groups.

Main Results:

• Mussel aggregation increased over time in both 6- and 72-hour trials, indicating a natural tendency to aggregate.
• After 72 hours, exposure to estradiol and mid-range atrazine concentrations significantly decreased mussel aggregation compared to controls.
• Specifically, estradiol and mid-ATR treatments reduced aggregation by 26% and 24%, respectively.

Conclusions:

• Ecologically relevant concentrations of atrazine can decrease aggregation behavior in freshwater mussels after 72-hour exposure.
• Estradiol exposure demonstrated a similar inhibitory effect on mussel aggregation.
• These findings suggest that atrazine may have ecological consequences on freshwater mussel populations by impacting aggregation, which is potentially linked to reproduction.