Tributyltin pollution biomonitoring under the Water Framework Directive: proposal of a multi-species tool to assess the ecological quality status of EU water bodies

Abstract

The Water Framework Directive (WFD) is a key legislative action developed by the European Unionin order to protect aquatic ecosystems. One of the concerning pollutants, listed in this directive as apriority hazardous substance, is tributyltin (TBT), a biocide largely used in antifouling paints and identifiedas a causative agent of imposex/intersex in gastropods. In order to integrate TBT pollution monitoringwithin this legislative framework, a practical exercise is here proposed to assess the evolution of surfacewater ecological status in Ria de Aveiro (NW Portugal). Three bioindicators – the caenogastropods Nucellalapillus, Nassarius reticulatus and Littorina littorea – were used under the general WFD benthic invertebratequality element, and the vas deferens sequence index (VDSI) and the intersex index (ISI) were selected asbiomarkers for the purpose of assessing the condition of this quality element regarding the impact of TBTpollution. Levels of VDSI in N. lapillus and N. reticulatus, and ISI in L. littorea, were surveyed in 2013 andcompared with previous data available for the same species and study area in 1998 and 2005, providing atime lapse for a period of 15 years. VDSI and ISI values were converted into Ecological Quality Ratios (EQR)and EQR boundaries were set for each species in order to define the five ecological status classes (High,Good, Moderate, Poor and Bad). We propose N. lapillus as key bioindicator, however the combined use offurther species is very useful to cover a wider study area. Based on the proposed method, it is concludedthat the ecological status of the surface waters surveyed in Ria de Aveiro, concerning the impact of TBTpollution on the above benthic invertebrate taxa, improved considerably since 1998 and achieved a GoodEcological Status in 2013, thus meeting the WFD environmental objectives for this priority hazardoussubstance even before 2015.