Effect of Bentazon on Growth and Physiological Responses of Marine Diatom: Chaetoceros gracilis

Abstract

The herbicide bentazon (CASRN 25057-89-0) is extensively used in agriculture in Brittany (France) to replace atrazine. Bentazon is not readily adsorbed by soil and therefore it enters adjacent freshwater ecosystems, making its way to estuarine and marine waters areas. Information regarding its effects on marine ecosystems is scarce. Phytotoxicity assessments were conducted in the laboratory on the common diatom Chaetoceros gracilis using both the active ingredient and its formulated product (Basamaïs). The 3 day EC₅₀ using cell counts were, respectively, 150 mg/L and 60 μg/L for bentazon active ingredient and for bentazon-formulated while cellular volume was increased. Although bentazon is known as a photosystem II inhibitor, it produced an increase of pigment (chlorophylls a, c, and carotenoids) content, ATP synthesis, rates of photosynthesis and respiration, and TBARS formation. Therefore, pigments cannot be used as biomarkers of toxicity. Algal cell recovery from bentazon effects occurred after 6–9 days, suggesting a tolerance mechanism.

KEYWORDS:

• ATP
• Bentazon
• Carotenoids
• Chaetoceros gracilis
• Chlorophylls
• Growth
• Marine diatom
• Photosynthesis

This research was financed by grants from the Ministère de l'Ecologie et du Développement Durable through the program ‘Evaluation et réduction des risques liés à l'utilisation des pesticides’. We certify that experiments needed for the work described in this manuscript have not required any study involving humans or animals.