Highly produced synthetic chemicals in the world used in the production of plastics (as e.g. Bisphenol A) have endocrine-disrupting (ED) effects in a variety of organisms, and being released into surface and ground waters, may pose the risk to freshwater ecosystems. Using freshwater ostracods (Ostracoda) to qualify ecological effects of ED compounds seems to be beneficial as these benthic microcrustaceans have been shown to be sensitive to toxic chemicals and compared to planktonic species may allow better understanding of the relationship between bioavailability of potentially hazardous substances and their ecotoxicological effects.

Ostracods are tiny crustaceans that live in most aquatic habitats in all marine and freshwater ecoregions of the world. Their body is protected and completely enclosed by shell formed by two (often strongly calcified) valves, and that is why they are sometimes known as seed shrimps or mussel shrimps. Non-marine species, usually less than 2 mm in size, are essentially benthic or nektobenthic and can be found in a variety of habitats from watering troughs for domestic livestock, pails and other artificial structures, through all kinds of natural permanent and temporary surface waters and various ground waters to thermal springs with water temperature reaching 50°C, damp moss and rainforest leaf litter. Ostracods feed chiefly on organic detritus but have a wide range of diets, including scavenger, carnivore or herbivore species, some of the latter are spinach lovers in laboratory cultures.

Ostracods plates
Scanning electron microscopy images of ostracods (Foto: Tadeusz Namiotko)

Ostracods have various important applications and are mostly known as one of the best palaeoenvironmental indicators. However, in recent years their value as sentinels of anthropogenically induced deteriorations of freshwaters, including different types of pollution, has also been recognised. Several laboratory experiments show high sensitivity of various non-marine ostracod species to heavy metals, pesticides or herbicides. A 6-day direct contact toxicity test for freshwater sediments (Ostracodtoxkit F manufactured by MicroBioTests Inc.) was even developed and accepted by the International Organisation for Standardization. However, new laboratory bioassays are needed to determine the long-term effects of several emerging pollutants on aquatic wildlife.

One of the principal examples of contaminants of emerging concern which are being discovered in freshwaters throughout Europe are endocrine disrupting compounds (EDCs). EDCs are substances that may interfere with the endocrine system and are found in a wide range of products used in everyday life. Recently, there has been growing interest among the scientific community in testing and learning the potential risk ECDs may pose to freshwater ecosystems. The most highly produced synthetic chemicals in the world with endocrine-disrupting effects are bisphenol A (BPA) used in the production of polycarbonate plastics or epoxy resins, and benzotriazole (BTA) used as a corrosion inhibitor. While a considerable number of studies have been published on BPA and BTA effects in experimental animals and humans, data on long-term toxicity to aquatic invertebrates are scarce.

The use of benthic ostracods, which may be exposed to higher BPA and BTA concentrations compared to pelagic species, allows better understanding of the relationship between bioavailability of these potentially hazardous substances and their ecotoxicological effects. Since contaminant-induced stress mechanisms and effects (including decreasing of fitness) are still poorly understood in invertebrates, whole-life-cycle tests are of outermost importance because they cover all sensitive stages and enlarge diversity of endpoints of potential toxicant effects. Such tests are currently one of the major and urgent recommendations of the Organisation for Economic Co-operation and Development.

The project Monitoring endocrine disruptors in surface waters of central Spain using toxicity and life history ostracod tests of IMDEA Water (within the Groundwater Ecology Group) aims at qualifying ecological effects and their application to toxicity testing of BPA and BTA on freshwater ostracods by performing laboratory experiments, including both, short- and long-term toxicity tests. In the short-term acute tests standard values that can be used for determining water quality will be assessed. In the partial- and whole-life-cycle tests several life history traits (hatching success, development time, survival, fecundity) will be monitored via exposure of water containing BPA and BTA at environmentally relevant concentrations. Final results of this study are intended to be used for developing standardized guidelines for testing toxicity of selected EDC on development and reproduction of freshwater ostracods, which eventually could be used as a support monitoring method for environmental risk assessment.

Acknowledgement: Talent Attraction Program contract no. 2016-T3/AMB-1951. Consejería de Educación, Juventud, y Deporte, Community of Madrid