The use of the biomarker imposex to assess the environmental status of aquatic ecosystems regarding tributyltin pollution

Abstract

Recent recommendations for the European Union (EU) directives concerning aquatic environment propose the use of effect based tools in pollution monitoring for a better integration of hydromorphological, chemical and biological data. In order to meet those recommendations, recent works proposed two different tools – based on the biomarker imposex – to asses TBT pollution under these directives. The present study applies these tools and evaluates its combined effectiveness on the assessment of TBT pollution, and the consequent definition of environmental status regarding this substance, in transitional water bodies: the Minho and Lima estuarine systems and adjacent coastal waters (NW Portugal). For this, in situ imposex levels and corresponding quality classes were assessed with the gastropod bioindicator species Nucella lapillus and Nassarius reticulatus, and a sediment bioassay with N. reticulatus, due to its burrowing behavior, was performed with sediments collected in both estuarine systems. A new ecological classification for this bioassay is proposed to categorize the ability of sediments to cause endocrine disruption effects in gastropods, due to the presence of TBT. Imposex expression allowed the identification of different environmental status in the two estuaries assessed, with Minho presenting “Good” status while inside the Lima estuary a “Moderate” to “At Best Poor” quality was evidenced. The sediment bioassay results were in accordance with the quality statuses obtained from the imposex assessment, Minho estuary presented non-contaminated sediments while in Lima toxic (BL1) and potentially toxic sediments (BL2, BL4 and BL7) were found. The combined use of these tools increases the surveyed area since the absence of imposex bioindicator species can be, sometimes, a shortcoming in TBT pollution biomonitoring. These results are discussed and the relevance of the biomarker imposex within EU Directives is highlighted.