Application of the European Water Framework Directive: Identification of reference sites and bioindicator fish species for mercury in tropical freshwater ecosystems (French Guiana)

• Published in: Ecological indicators 2019-11, Vol.106, p.105468, Article 105468
• Main Authors: Gentès, Sophie, Coquery, Marina, Vigouroux, Régis, Hanquiez, Vincent, Allard, Luc, Maury-Brachet, Régine
• Format: Article
• Language: English
• Subjects: Bioindicator; Environmental Quality Standard; Environmental Sciences; Fish; Mercury; Priority substance; Tropical freshwater
• ISSN: 1470-160X; 1872-7034
• DOI: 10.1016/j.ecolind.2019.105468

•Mercury (Hg) levels were measured in 6208 fish in French Guiana (creeks and rivers)•All fish in creeks and 84% in rivers had Hg concentration above the EQSbiota.•Seven reference sites on creeks and two areas on rivers were identified for Hg.•Bioindicator fish species/genera for Hg are proposed to allow the WFD implementation.•Background Hg concentrations were defined in the selected bioindicator fish species. Mercury (Hg) is a toxic metal subject to several international regulations. The European Water Framework Directive (WFD) established in 2008 an Environmental Quality Standard for biota (EQSbiota) at 0.02 µg.g−1 fresh weight. This standard is not always adapted, such as in French Guiana subjected to high natural background Hg levels and intensive illegal gold mining. Therefore, this study focuses on how to apply the WFD for the definition of good chemical status (i.e., EQSbiota) in a context of strong and generalized natural and anthropic Hg contamination. Based on Hg concentrations measured in 6208 fish over >200 sites between 2004 and 2015, we first aimed at discriminating the natural or anthropogenic influences at each site. Then, as WFD recommends considering only high trophic level fish species as bioindicator species, we selected carnivorous/piscivorous fish species able to significantly accumulate Hg and discriminate reference sites from gold mining polluted sites. Total Hg concentrations measured in fish muscle were mostly above the EQSbiota (100% for creeks and 84% for rivers), confirming the unsuitability of the direct application of this standard in French Guiana. Among the studied sites, few potential reference sites were identified: eight sites spread over six different watersheds for creeks, and only two areas (group of sites) both on the Oyapock watershed for rivers. Several relevant bioindicators fish species are proposed: ten species (over 35 species tested) belonging to seven genera on creeks (Moenkhausia oligolepis, Gymnotus carapo, Sternopygus macrurus, Jupiaba [abramoides + keithi], Pimelodella [cristata + geryi + macturki], Copella carsevennensis, Pyrrhulina filamentosa.), and four species (over 21 species tested) belonging to three genera on rivers (Acestrorhyncus [micropelis + falcatus], Hoplias aïmara, Ageneiosus inermis). In order to facilitate field sampling, difficult in such remote hydrosystems, and to improve results interpretation, we tested the possibility to group some of these species. Our results indicate that only J