title: Assessment of toxicity thresholds in aquatic environments: does benthic growth of diatoms affect their exposure and sensitivity to herbicides?
abstract: Benthic diatoms evolved in a biofilm structure, at the interface between water and substrata. Biofilms can adsorb toxicants, such as herbicides, but little is known about the exposure of biofilm organisms, such as benthic diatoms, to these adsorbed herbicides. We assessed the sensitivity of 11 benthic diatoms species to 6 herbicides under both planktonic and benthic conditions using single-species bioassays. The concentration that reduced the growth rate of the population by 10% (EC10) and 50% (EC50), respectively, varied depending on the species, the herbicides, and the growth forms involved. As a general trend, the more hydrophobic the herbicide, the more species were found to be sensitive under benthic growth conditions. Statistical differences (alpha<5%) were observed between the sensitivities under planktonic and benthic growth conditions for many hydrophobic herbicides. A protective effect of the biofilm against herbicides was observed, and this tended to decrease (at both the EC10 and EC50 levels) with increasing hydrophobicity. The biofilm matrix appeared to control exposure to herbicides, and consequently their toxicity towards benthic diatoms. For metolachlor, terbutryn and irgarol, benthic thresholds derived from species sensitivity distributions were more protective than planktonic thresholds. For hydrophobic herbicides, deriving sensitivity thresholds from data obtained under benthic growth seems to offer a promising alternative.
authors.affiliation: INRA, UMR Carrtel, F-74203 Thonon, France; Université de savoie, UMR Carrtel, F-73011 Chambéry, France. Electronic address: floriane.larras@thonon.inra.fr.
authors.forename: Floriane
authors.initials: F
authors.lastname: Larras
authors.forename: Bernard
authors.initials: B
authors.lastname: Montuelle
authors.forename: Agnès
authors.initials: A
authors.lastname: Bouchez
mesh_terms: D000081:Acetamides / Q000633:toxicity; D001280:Atrazine / Q000633:toxicity; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development; D001681:Biological Assay; D017377:Diatoms / Q000187:drug effects* / Q000254:growth & development; D004237:Diuron / Q000633:toxicity; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000633:toxicity*; D010671:Phenylurea Compounds / Q000633:toxicity; D014227:Triazines / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D000081:Acetamides; D006540:Herbicides; D010671:Phenylurea Compounds; D014227:Triazines; D014874:Water Pollutants, Chemical; C103341:irgarol 1051; C028904:isoproturon; D004237:Diuron; D001280:Atrazine; C051786:metolachlor; C010347:terbutryne
keywords: Benthic diatoms; Bioassays; Biofilm; Herbicides; Risk assessment