Portugal is a Southwest European country which benefits from its temperate climate, with average temperatures in winter of 9-14 C and 20-30 C in summer and from an extensive coastline, the west coast ca. 600 km and the south coast ca. 200 km, facing the Atlantic Ocean. It is not surprising though, that seaside activity are specially practised in particular sun bathing. From June to September the official bathing season starts and brings maybe 50% of the population to the beaches.
Many industries need a place on the coast to settle such as oil refinery plants and their treated or untreated wastewaters are thrown into the sea. Besides industry, urban areas expanded towards the coastal zone and consequently the coastline has received an increasing pressure of organic load and pollutants.

It is well known, at present, that many beaches do not fulfil the requirements for health safety due mainly to pollution from industries and domestic sewage outfall from the cities. Sewage water treatment plants are insufficient to treat the organic load from the cities and villages and the wastes end up in the sea.

Some beaches in the north part of Portugal have sewage wastewater running through their sands because the sewage water pipelines are poorly maintained or in other cases do not exist at all. Freshwater streams also contribute to the contamination of the sands in the beach.
Aterro Beach is one of these beaches located about 8 km northwards of Porto at Leça da Palmeira, close to an oil refinery plant. A water stream coming from land and running into the sea crosses the beach. It was in this stream that an oil slick was observed. The sands in the stream bed were black, the stream water had a sheen of oil and on the edge of the stream, black sediments laid below 1 cm of white sands. It becomes high priority to monitor these areas to protect human health and the marine life.

Polycyclic aromatic hydrocarbons (PAHs) represent a relatively small percentage, of petroleum constituents, their presence in fuel is fundamental to make the combustion inside the vehicle’s engines to become less explosive and more efficient [1], however some PAHs are known by their toxicity and carcinogenicity to mammals and aquatic life. They have been designated as priority pollutants by the American Environmental Protection Agency (EPA). As the name suggests, these compounds are cyclic, made of benzene rings linked together, the simplest PAH has two rings, naphthalene, and the complexity increases with the number of rings attached to the molecule. Their physical/chemical properties are important features, which determine their fate and behaviour in the different components of the ecosystem, water, sands or living organisms. They are water insoluble due to their low polarity and in consequence they can be found adsorbed onto sediments or surfaces and they are also prone to be taken up by organisms. The simpler PAHs are volatile and are the first to disappear from an oil spill when it sets fire, but the more complex ones with higher molecular weights they are persistent in the environment. They have very slow rates of microbial degradation and can be accumulated in the sediments for long time or in the tissues of living organisms. They enter through the cellular membranes of organisms and can be transferred and magnified through the food chain when taken by the predators.

The effects of polycyclic aromatic hydrocarbons in living organisms, particularly in marine mussels have been described as direct effects such as narcosis of the cilia and muscles, causing a decrease or impairment of the feeding rate. In consequence the energy available for growth and reproduction will be reduced. At the cellular level PAHs can alter fluidity and permeability of membranes and cause disturbance in the structure and function of the lysosomes, the organelle responsible to produce digestive enzymes. Injury of lysosomal membrane occurs and the release of hydrolytic enzymes leads to cell damage and possibly cell death [2].

Some scientists have been studied ways of recognising the origin of contaminants from their distribution and predominance. Because these classes of pollutants can have either a petrogenic or pyrolytic origin it is a step forward in environmental chemistry to be able to identify the source of pollution. Lower temperature generation of PAHs leads to abundant formation of alkyl-substituted compounds whereas high temperature processes generate mainly unsubstituted compounds. This has been accomplished by calculating some indices, the ratio of the relative concentration of the typical pyrolytic 4,5-methylene phenanthrene to the total concentration of methylphenanthrenes. High values of this index gives indication that the sample has formed in high temperature processes, while low values are indicative of the presence of petroleum samples [3]. Another index is the ratio of phenanthrene concentration to anthracene concentration (P/A). Due to the high isomeric stability of phenanthrene, high temperature processes such as combustion, gives rise to P/A < 10, whereas slow maturation processes like diagenesis originate P/A > 15. The ratio of fluoranthene concentration to pyrene concentration can also give similar information on the possible source of PAHs. If this index Flt/Pyr > 1, the sample was pyrolytic generated, if Flt/Pyr < 1 it indicates petroleum hydrocarbon signature [4].

A study was conducted at Aterro Beach to evaluate the presence and extent of petroleum contaminants, in particular (PAHs), in the sands and mussel tissues. Samples were collected and analysed by standardised methods and revealed high concentrations of these aromatic compounds. The sixteen polycyclic aromatic hydrocarbons measured monthly were: naphthalene (Nap), acenaphthylene (Acy), acenaphthene/fluorene (Flu+Ace) phenanthrene (Phe), anthracene (Ant), fluoranthene (Flt), pyrene (Pir), benzo(a)anthracene (BaA), chrysene (Chr), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), dibenzo(a,h)anthracene (dBA), benzo(g,h,i)perylene (Bpe) and indeno(123-cd)pyrene (Ind) and 13 of these PAHs were present in the sediments. Their concentrations varied in time in the range 30-1200 ng·g-1 of sediment and the most abundant compound was acenaphthylene (13-580 ng·g-1). The sum of PAHs reached their maximum concentrations in July when the sediments were black tainted in the streambed crossing the beach. When these values are compared to the ones from a reference site, these represent an increase of two orders of magnitude relative to the reference. The molecular ratio Flt/Pyr was calculated for sediments and it gave values less than 1 from May to July, suggesting petroleum hydrocarbons contamination rather than pyrolytic contamination. Overall, the levels of contamination in the sediments were high but well below the values reported from harbour sediments of extensive ship traffic (10-100 µg·g-1)[5].

In the mussel tissues from Aterro Beach all the 16 PAHs under study were present in high concentrations 3700-17000 ng·g-1. In the same way as we compared the concentrations of PAHs in the sediments from a contaminated site to a non-contaminated one, the comparison between mussel tissues gave a different result. The difference between clean and contaminated mussels is not so striking. Mussels from the reference site had total concentration of PAHs varying with time between 1500-6500 ng·g-1 of dry weight. Although the highest concentration was considerably lower than in the contaminated mussels, the magnitude of PAHs concentrations in clean mussels is at most 10 times below that of contaminated mussels.

The range of concentrations of PAHs found in this study for mussels can be considered high when compared to mussels living in polluted conditions of the French coast where PAHs values range 60-370 ngg-1. The PAHs accumulated in the mussel tissues is the result of several routes of input including contamination from the sediments, from the food particles and even from the water column. This observation opens way for discussion on the importance of assessing the contamination in the living organisms besides the other elements of their habitat. It also stresses the need to investigate early warning monitoring tools such as cellular and molecular biomarkers to evaluate cellular damage prior to higher level of organisation disruption.

References

[1] Raymond Chang, Chemistry, 1994. McGraw-Hill, Inc. 5th Ed.
[2] Usha Varanasi, Metabolism of Polycyclic Aromatic Hydrocarbons in the Aquatic Environment, 1989. CRC Press.
[3] P. Garrigues et al., 1995. Polycyclic Aromatic Hydrocarbons, 7, 275.
[4] P. Baumard et al. , 1998. Environ. Toxicol. Chem., 17, 765.
[5] S. E. McGroddy et al., 1996. Environ. Sci. Technol., 30 172.

   

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