Organic contaminants in the Mondego estuary fish assemblage

Abstract

The main objective of this thesis was to study PCBs and HCB accumulation in an estuarine fish assemblage. PCBs and HCB are contaminants very persistent in the environment. Their high stability can lead to a relatively long half-live, low metabolic transformation and hydrophobicity. These contaminants are very lipophilic, therefore they tend to accumulate in organisms, including fish. PCBs are constituted by 209 congeners. In the present thesis the most abundant congeners were CB 138, 153 and 180. These congeners are high chlorinated congeners, therefore very persistent in the environment and in biological samples. Estuaries are very important ecosystems, since they provide several habitats for many comercial species, particularly fish. Fishes can use estuaries as migration routes, refuge against predators and nursery grounds. However, estuaries are exposed to high anthropogenic activities, which can lead to a high uptake of contaminants. The Mondego estuary is a small estuary located in the western coast of Portugal, with limited and diffuse contamination sources. The main contamination sources are wastewaters, from domestic and industrial sewage, fertilizers and pesticides, from agricultural runoff, and the Figueira da Foz harbour. In chapter 1 an introduction to the topic of HCB and PCBs is presented highlighting their importance in the natural environment. Chapter 2 addresses a study performed in the Mondego estuary fish community. No studies regarding the concentration of PCBs in the whole fish community had been made so far, therefore this study fills a gap in knowledge in how PCBs are distributed in fish assemblages. Species that spent more than three years in the estuary presented higher concentration, than species that spent less than three years in the estuary. Furthermore, a positive correlation was found between lipid content and concentration. So the main factors influencing PCBs accumulation in the Mondego estuary were the time spent in the estuary, lipid content and dietary intake. Chapter 3 addresses two studies performed in mullet species, Liza ramada, Liza aurata and Chelon labrosus. Both studies were performed along the species lifespan and in PCBs. In the first study L. ramada and L. aurata increased their concentration with age. Among the three mullet species L. ramada presented the highest concentration, which could be attributed to the fact that this species spent more time inside the estuary then the other two species. In the second study C. labrosus PCBs concentrations’ were analyzed in both genders, in liver and muscle. No significant differences were found in both sexes and tissues concentration, although males increased their concentration with age. Liver presented higher concentration than muscle. Chapter 4 addresses a study regarding PCBs and HCB concentration in Platichthys flesus from the Mondego estuary and adjacent coastal water. P. flesus was analyzed along its lifespan, in three tissues, muscle, liver and gills. PCBs concentration decreased along its lifespan, in all tissues. HCB concentration was only detected in older fishes from the adjacent coastal water, and its concentration inceased with age. Liver and gills presented the highest concentration followed by the muscle, for both contaminants. Most fish species analyzed in this thesis were commercial species, therefore consumed by humans. Regarding PCBs all studied species presented low concentration and below the regulation limit establish by the European Union, 75 ng g-1 (wet wt). P. flesus daily intake was also below the regulation limit of US Department of Health and Human Services, regarding HCB, and WHO tolerance limit, regarding PCBs. Therefore, fishes from the Mondego estuary are considered safe for human intake.