RESUMO
A pipe rupture during unloading led to a spillage of 350-700 tonnes of Caño Limon, a light sweet crude oil, into San Vicente Bay in 2007. Initial clean-up methods removed the majority of the oil from the sandy beaches although some oil remained on the rocky shores. It was necessary for the responsible party to clean the spilled oil even though at this location there were already crude oil hydrocarbons from previous industrial activity. A biosolvent based on vegetable oil derivatives was used to solubilise the remaining oil and a statistical approach to source apportionment was used to determine the efficacy of the cleaning. Sediment and contaminated rock samples were taken prior to cleaning and again at the same locations two days after application of the biosolvent. The oil was extracted using a modified USEPA Method 3550B. The alkanes were quantified together with oil biomarkers on a GC-MS. The contribution that Caño Limon made to the total oil hydrocarbons was calculated from a Partial Least Squares (PLS) analysis using Caño Limon crude oil as the source. By the time the biosolvent was applied, there had already been some attenuation of the oil with all alkanes Assuntos
Monitoramento Ambiental/métodos
, Recuperação e Remediação Ambiental
, Poluição por Petróleo/análise
, Petróleo/análise
, Poluentes Químicos da Água/análise
, Baías/química
, Chile
, Análise dos Mínimos Quadrados
, Poluição Química da Água/estatística & dados numéricos
RESUMO
Aquaculture activities in southern Chile demand floating devices to produce electricity powered by diesel generators. It has been recently proposed to replace this fuel with propane. However, little is known about the behaviour and possible environmental impacts of an accidental release of propane underwater. In this study we evaluated the impact of water temperature and salinity on the saturation and further release of propane under controlled laboratory experiments. Results showed that under extreme environmentally relevant scenarios (high and low temperature and salinity), propane saturated the water more quickly. However, while it is important to consider that saturation times can be similar (â¼2 h), the magnitudes of propane dissolved can be different. Experiments showed that cold waters (5 °C) propane is dissolved twice than warm waters (20 °C). Residence time was more affected by water temperature and almost independent of water salinity. Propane may take at least 2 days to be released from waters (around 90% of the initial amount dissolved under laboratory conditions). Additionally, we evaluated the impact on dissolved oxygen displacement and the embryotoxicity of the dissolved fraction by using Zebrafish Embryo Toxicity Assay. Results showed that dissolved oxygen was quickly removed. However, the levels of dissolved oxygen were promptly recovered in the studied systems. We also observed that propane can generate genotoxic effects (3-10% mortality), but after 2 days the system can be almost free of propane and the effects may become much lower. Comparatively with the literature, propane showed to be less toxic than diesel and it is a viable and less environmentally hazardous replacement for diesel.
Assuntos
Propano , Peixe-Zebra , Animais , Chile , Meio Ambiente , Propano/toxicidade , SalinidadeRESUMO
To investigate the potential sources of fatty alcohols arriving at a WWTP and entering the receiving waters, a study was conducted at Treborth North Wales using compound specific stable isotope mass spectrometry (¹³C and ²H). Samples were collected from soils, marine sediments, detergents used in the catchment and in the WWTP. Total fatty alcohol concentrations decreased in the liquid phases through the treatment works with the majority of the compounds accumulating in the sludge (biosolids). Natural plant based detergents have δ¹³C values between -26 and -32 while petroleum-based detergents occupy a range between -25 and -30. The corresponding δ²H values are -250 for natural sourced materials and -50 for oil-based detergents which enable these two sources to be separated. The influent to the WWTP contained fatty alcohols which originated mainly from faecal sources and natural surfactants (â¼75%) with a smaller amount potentially derived from petroleum-based surfactants (â¼25%). The effluents from the WWTP contained mainly short chain compounds with a chain length less than C¹6. Their δ²H stable isotope signature was different to the other potential sources examined and suggests bacterial synthesis during the treatment processes. The sludge had relatively high concentrations of fatty alcohols as would be expected from their low water solubility. The stable isotopic signatures were consistent with a mixture of faecal and detergent sources. The sludge in this area is routinely spread on agricultural land as a fertiliser and may find its way back into the sea via land runoff. On the basis of the mean discharge rates and the mean C12 concentration in the effluent, this WWTP would contribute â¼300 g day⻹ to the receiving waters. The marine sediment samples had short chain fatty alcohols that are typical of marine production and with stable isotope values that indicate exclusive marine production for the C14 potentially mixed with terrestrial sources for the C16 and C18 compounds. Therefore, the fatty alcohols in the marine sediments are not the same as those that were discharged in the liquid effluent and these fatty alcohols were not the ones that entered the works through the influent but were synthesised or recycled within the works.
Assuntos
Detergentes/análise , Álcoois Graxos/análise , Sedimentos Geológicos/química , Esgotos/química , Poluentes da Água/análise , Isótopos de Carbono , Detergentes/química , Álcoois Graxos/química , Solo , País de Gales , Poluentes da Água/químicaRESUMO
Volatile Organic Compounds (VOCs) in the marine environment are produced by biogenic sources (marine macroalgae, phytoplankton, sediments, etc.) as well from anthropogenic sources. The temporal variation of such VOCs was studied together with their relationship to biological, meteorological and physico-chemical factors. Sixty four different VOCs were quantified including halogenated (Assuntos
Monitoramento Ambiental/métodos
, Água do Mar/química
, Compostos Orgânicos Voláteis/química
, Poluição Química da Água/análise
, Fitoplâncton
, Pigmentos Biológicos
, Fatores de Tempo
, Reino Unido
, Movimentos da Água
, Vento
RESUMO
Electronic waste (e-waste) is informally processed and recycled in Agbogbloshie in Accra (Ghana), which may be the largest such site in West Africa. This industry can lead to significant environmental contamination. In this study, surface dust samples were collected at a range of sites within Accra to establish the offsite consequences of such activities. Fifty-one samples were collected and analysed for 69 elements by ICP-mass spectrometry after nitric acid digestion. The data indicated a significant enrichment in metals associated with solder and copper wire at the site itself and a downwind dispersion of this source material to a distance of approximately 2.0 km. Chlorine and bromine were also elevated at this site as residues from polyvinyl chloride combustion and flame retardants respectively. The elemental composition indicated that only low technology electrical equipment was being treated this way. Multivariate statistical analyses by principal components analysis and polytopic vector analysis identified three sources contributing to the system; (i) burn site residue dispersing within 2 km from the source site, (ii) marine matter on the beaches alone and (iii) the baseline soil conditions of the city of Accra. Risk ratios and hazard quotients developed from the measured concentrations indicated that copper was providing the greatest risk to inhabitants in most cases although nickel, vanadium, chromium and zinc also contributed.
Assuntos
Resíduo Eletrônico/análise , Monitoramento Ambiental/métodos , Metais Pesados/análise , Reciclagem , Poluentes do Solo/análise , Solo/química , Cromo/análise , Cobre/análise , Monitoramento Ambiental/estatística & dados numéricos , Gana , Análise Multivariada , Níquel/análiseRESUMO
Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzo-p-furans (PCDF) are widely distributed in the environment. The diverse production processes that form these compounds lead to a range of chemical signatures although weathering may cause changes to these signature over time and with increasing distance from their origin. Chemical signatures in sediments based on 17 PCDD/Fs were developed in Concepcion, a Chilean city in the middle of a complex hydrological system which contains several small urban freshwater bodies and the River Bio-Bio. The region has numerous industrial and domestic activities that may contribute PCDD/Fs to the environment. Sediments from urban lakes had higher concentrations of dioxins and furans (mean=941ng·kg-1) than either a remote lake (335ng·kg-1) located 32km from the city or marine samples (mean=124ng·kg-1). Up to 85% of the compounds present in all sediment samples could be explained by the chemical signature associated with airborne particulates leaving only 15-30% of the chemical signature potentially arising from other sources. The remote lake had higher proportions of the less-chlorinated compounds compared to the urban samples.
RESUMO
The presence of the radionuclide (99)Tc in the marine environment is of concern to environmental scientists because of its conservative nature and high concentration factor in commercially valuable species. The brown seaweed Ascophyllum nodosum (Linnaeus) Le Jolis was used to biomonitor the spatial distribution of (99)Tc around the Welsh coast, an area relatively unstudied with respect to this isotope. Over the course of a year an inverse relationship was observed between the (99)Tc concentration in A. nodosum samples and approximate straight-line distance from Sellafield. These data show that detectable levels of a Sellafield derived radionuclide are reaching the Welsh coast despite the overall northward movement of the Sellafield plume.
Assuntos
Ascophyllum/química , Tecnécio/análise , País de GalesRESUMO
The occurrence of airborne particulate matter has been flagged as "of concern" in several megacities, especially in Asia. Selected Chilean regions have similar problems as wood burning is the major source of heating in homes. This concern has led to mitigation measures restricting the burning of wood at periods when the particulate matter smaller than 2.5 µm (PM2.5) concentrations are predicted to be high. This work investigates the linkage between indoor and outdoor particle concentrations, determines their source through the polyaromatic hydrocarbon (PAH) signature and investigates the efficacy of the current management practice of burning restrictions. The PM2.5 fraction was collected at 12 different properties with coincident indoor and outdoor sampling using a low-volume active sampler for 24 hours. Indoor concentrations of PM2.5 ranged from 6 to 194 µg m(-3) with a mean of 72 µg m(-3) and corresponding outdoor concentrations ranged from 5 to 367 µg m(-3) with a mean of 85 µg m(-3) over the winter periods of 2014 and 2015; the Chilean national permitted maximum in outdoor air is 50 µg m(-3) in 24 hours. Higher concentrations were measured when the outdoor air temperature was lower. The PAHs were analysed on the PM2.5 fraction; the indoor concentrations ranged from 2 to 291 ng m(-3) with a mean of 51 ng m(-3) compared to an outdoor concentration between 3 and 365 ng m(-3) with a mean of 71 ng m(-3). Multivariate statistical analysis of the PAH profiles using principal components analysis (PCA) and polytopic vector analysis (PVA) identified wood burning, static and mobile diesel emissions and kerosene combustion as the major contributors to the particulate matter. When converted to toxicity equivalents (BaP-TEQ), the highest toxicity arising from PAHs in the indoor air was associated with a property that used a "leaky" combined wood stove and heater and also used a wood-fired brazier for local heating. In outdoor air, there was a relationship between the housing density and the BaP-TEQ, such that denser housing had higher BaP-TEQ values. The restrictions in wood burning on selected days may have had a measureable effect on the PM2.5 concentrations in that region but the effects were small and only present for the day of the restriction.
Assuntos
Poluentes Atmosféricos/análise , Poluentes Atmosféricos/toxicidade , Poluição do Ar em Ambientes Fechados/análise , Material Particulado/análise , Material Particulado/toxicidade , Hidrocarbonetos Policíclicos Aromáticos/análise , Hidrocarbonetos Policíclicos Aromáticos/toxicidade , Chile , Exposição Ambiental , Monitoramento Ambiental , Calefação , Habitação , Análise de Componente Principal , Estações do Ano , Madeira/química , Madeira/toxicidadeRESUMO
Since sewage discharges can significantly contribute to the contaminant loadings in coastal areas, it is important to identify sources, pathways and environmental sinks. Sterol and fatty alcohol biomarkers were quantified in source materials, suspended sediments and settling matter from the Ria Formosa Lagoon. Simple ratios between key biomarkers including 5beta-coprostanol, cholesterol and epi-coprostanol were able to identify the sewage sources and effected deposition sites. Multivariate methods (PCA) were used to identify co-varying sites. PLS analysis using the sewage discharge as the signature indicated approximately 25% of the variance in the sites could be predicted by the sewage signature. A new source of sewage derived organic matter was found with a high sewage predictable signature. The suspended sediments had relatively low sewage signatures as the material was diluted with other organic matter from in situ production. From a management viewpoint, PLS provides a useful tool in identifying the pathways and accumulation sites for such contaminants.
Assuntos
Monitoramento Ambiental/métodos , Esgotos , Gerenciamento de Resíduos/métodos , Eutrofização , Ácidos Graxos/análise , Sedimentos Geológicos , Humanos , Análise dos Mínimos Quadrados , Rios , Esteróis/análise , Movimentos da Água , Purificação da ÁguaRESUMO
A series of laboratory experiments were carried out to test the potential of vegetable oil biodiesel for the cleaning of oiled shorelines. In batch experiments, biodiesel was shown to have a considerable capacity to dissolve crude oil, which appears to be dependent on the type of biodiesel used. Pure vegetable oil biodiesels (rapeseed and soybean) were significantly more effective in the cleanup of oiled sands (up to 96%) than recycled waste cooking oil biodiesel (70%). In microcosm and mesocosm experiments, oiled sediments were sprayed with biodiesel and subjected to simulated tides. Microcosm experiments revealed that, of those tested, the highest ratio of biodiesel to crude oil, had the highest effectiveness for cleaning fine sands, with ratios of 2:1 (biodiesel:crude oil) giving the best results. In the mesocosm experiments a ratio 1:1 of soybean biodiesel to crude oil removed 80% of the oil in cobbles and fine sands, 50% in coarse sand and 30% in gravel. Most of the oil was removed with the surface water, with only a small amount being flushed through the sediments. Particle size and pore size were important determinants in the cleanup and mobility of crude oil in the sediments in these static systems. It is expected that the biodiesel effectiveness should improve in the natural environment particularly in exposed beaches with strong wave action. However, more laboratory and field trials are required to confirm the operational use of biodiesel as a shoreline cleaner.
Assuntos
Poluição Ambiental/prevenção & controle , Óleos de Plantas/química , Tamanho da Partícula , Petróleo , Dióxido de Silício , Movimentos da ÁguaRESUMO
The effects of a simulated spill of sunflower oil in salt marsh sediments were compared with an experiment with linseed oil. Sunflower and linseed oil penetrated the sediments at the same rates but different adsorption of the oils onto sediment particles resulted in the establishment of anaerobic conditions at shallower depths in sediments contaminated with linseed oil than with sunflower oil. The total lipid content of sunflower oil contaminated sediments remained almost stable for 6 months, whilst only 40% of linseed oil remained in the sediment after 2 months. Numbers of culturable heterotrophic bacteria and aerobic oil degrading bacteria in muddy sediment increased rapidly in response to the presence of the oils but bacterial numbers in sandy sediments increased more slowly for sunflower oil. Changes in fatty acid composition indicate similar degradation pathways for both oils but sunflower oil degraded more slowly than linseed oil and thus has the potential for longer lasting effects in marine environments.
Assuntos
Sedimentos Geológicos/química , Óleo de Semente do Linho/análise , Óleos de Plantas/análise , Adsorção , Bactérias Aeróbias/metabolismo , Bactérias Aeróbias/fisiologia , Biodegradação Ambiental , Ecossistema , Monitoramento Ambiental , Ácidos Graxos/química , Sedimentos Geológicos/microbiologia , Concentração de Íons de Hidrogênio , Cinética , Óleo de Semente do Linho/metabolismo , Oxirredução , Óleos de Plantas/metabolismo , Óleo de Girassol , TemperaturaRESUMO
In a simulated spill in a salt marsh, linseed oil penetrated rapidly into the sediments at a rate of 10(-7) cm2 s(-1). The oil concentration remained unchanged for the first month after the spill, but 60% of the oil disappeared from the top 30 cm after a further month. The oil adsorbed to and accumulated in the muddy sediments (top 15 cm) leading to decreased sediment permeability, pH, Eh, abundance of plant roots and infauna and to the establishment of anoxic conditions. These changes accompanied transformations in the original fatty acid composition of the linseed oil, mainly associated with a decrease in 18 : 3omega3, an increase in the other fatty acids and the presence of 'new' fatty acids. A rapid increase in the abundance of heterotrophic aerobic and anaerobic bacteria and aerobic oil degrading bacteria, suggested that these micro-organisms degraded the oil. The role of the bacteria in oil degradation was confirmed in laboratory experiments where the fatty acids composition of the linseed oil underwent identical transformations to those obtained in the field. The degradation of linseed oil appears to be a sequential process initiated by aerobic and/or anaerobic bacteria and continued by sulphate reducing bacteria, which were unable to degrade the raw oil.
Assuntos
Ecossistema , Sedimentos Geológicos/química , Óleo de Semente do Linho/metabolismo , Bactérias Aeróbias/fisiologia , Bactérias Anaeróbias/fisiologia , Biodegradação Ambiental , Monitoramento Ambiental , Ácidos Graxos/química , Concentração de Íons de Hidrogênio , Óleo de Semente do Linho/efeitos adversos , Permeabilidade , Bactérias Redutoras de Enxofre/fisiologiaRESUMO
Fatty alcohol-based surfactants are widely used in detergents and personal care products; they are typically disposed of down-the-drain and are degraded or removed during wastewater treatment. Analytical data had shown concentration and profile differences between regions of the United States. Market sales data were purchased relevant to the sampling dates. In combination with analysis of the fatty alcohol profiles in the top selling products, the influent profiles were reconstructed and compared to the whole U.S. sales data. The per capita usage rate for fatty alcohols through these 4000+ top selling products was 4.9 g per day, with 88% arising from liquid laundry detergents and hand dish detergents. This extrapolates to a national usage of 185,000 tonnes per year. There were significant differences in the purchasing habits of the inhabitants across the four regions sampled, although this had minimal impact on the fatty alcohol profile which was dominated by the C12 moiety. The U.S. market was also dominated by petrochemically-sourced chemicals. This market forensics approach using purchased sales data was able to extend our knowledge of the fate of these chemicals without a major (expensive) sampling and analytical campaign.
Assuntos
Cosméticos/análise , Detergentes/análise , Álcoois Graxos/análise , Águas Residuárias/química , Poluentes Químicos da Água/análise , Monitoramento Ambiental , LavanderiaRESUMO
Samples of influent, effluent and sediments of the receiving waters of eight WWTPs were collected in each of three eco-regions of the USA, a total of 24 facilities. Six different treatment technologies were included to determine the fate of anthropogenic fatty alcohols. The lipids were analysed by compound-specific stable isotope ratio mass spectrometry. There were significant differences in the profiles of the influent among eco-regions, due to differences in the products used within the catchment, the diets of the inhabitants, or in-pipe processes. The sediments of all the receiving waters had similar fatty alcohol profiles, with terrestrial plant matter dominating and secondary contributions from algal and bacterial synthesis. Any contributions from the WWTP liquid effluents were small (<1%) and not from the original fatty alcohols suite in the influent. These compounds might have the same chain lengths, but they have different stable isotopic signatures. The type of secondary treatment did not affect the removal of fatty alcohols and the sediments of the receiving waters were dominated by terrestrial plant inputs; the eco-region may affect the profile of the influents but not the stable isotopes. The ecological risk from the use of these particular chemicals, which are disposed of down the drain, is minimal.
Assuntos
Monitoramento Ambiental , Álcoois Graxos/análise , Tensoativos/análise , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/análise , Álcoois Graxos/química , Tensoativos/químicaAssuntos
Ecossistema , Fontes Geradoras de Energia , Monitoramento Ambiental , Óleos Combustíveis , Produtos Agrícolas , Fontes Geradoras de Energia/economia , Fontes Geradoras de Energia/ética , Óleos Combustíveis/economia , Óleos Combustíveis/provisão & distribuição , Óleos Combustíveis/toxicidade , PlantasRESUMO
Fatty alcohols are naturally produced hydrocarbons present in all living organisms. They are also used in detergent and cosmetic formulations, may be sourced from either petroleum or biological materials, and are typically disposed of down the drain. This study was conducted on the Luray catchment, Virginia, USA, where sales data indicate that approximately 2 kg of fatty alcohols from detergent enter the wastewater every day. Reconstructing fatty alcohols in the influent on the basis of sales data indicated a mix of odd and even chain compounds, with C(12) being dominant. This profile was influenced strongly by liquid laundry detergents (69%). Sediment and soil samples from the catchment were analyzed by gas chromatography-mass spectrometry and by stable isotope ratio mass spectrometry to determine the δ(13)C and δ(2)H signatures. The long-chain components in agricultural soils and river sediments were distinguishable clearly from the algal fatty alcohols produced within the river system. The wastewater was a mixture of fecal and detergent sources of fatty alcohols in a ratio of 75:25%. The fatty alcohols in the effluent had different stable isotopic signatures and chain-length profiles from the influent, indicating that these compounds are not the same as those that entered the treatment plant. The total quantity of fatty alcohols leaving the treatment plant through the effluent pipe was low compared with the input. Analysis of the contributions based on the stable isotopes and profiles suggests that of the fatty alcohols present in the river system downstream of the treatment plant, 84% were derived from terrestrial plant production, 15% came from in situ algal synthesis, and 1% were derived from the effluent.
Assuntos
Álcoois Graxos/análise , Poluentes do Solo/análise , Águas Residuárias/análise , Detergentes/análise , Cromatografia Gasosa-Espectrometria de Massas , Hidrocarbonetos , Espectrometria de Massas , Petróleo/análise , Solo/química , Virginia , Águas Residuárias/estatística & dados numéricosRESUMO
Analyses of trace metals in benthic sediments from selected fjords and channels between 41 degrees 30' and 46 degrees 50'S, 75 degrees -72.3 degrees W were made after the CIMAR 1 Fjords expedition co-ordinated by CONA-Chile in 1995; the metals analyzed include Ba, Cd, Co, Cr, Cu, Ni, Pb, Sr, V and Zn. The objective of this study was to establish baseline values for these metals and to compare them with similar studies made in comparable, but geographically distinct, environments. Box core samples were collected at 35 stations and metal analysis was by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) using the MESS-2 reference standard. The ranked abundance by metal was Ba >> Sr >> V > Zn > Cr > Cu approximately Ni approximately Pb > Co >> Cd; these metals were not homogenous across the region and coefficients of variation were >10%. There were distinct groupings by metal and geographical area including the fjords, basins and channels. Depth profiles of the metal concentrations also varied spatially, e.g. Guafo, Laguna San Rafael, Moraleda, Corcovado, Quitralco, and Jacaf were predominantly homogeneous with depth profiles indicative of pristine systems experiencing few human impacts. In contrast, Aysen, Cupquelan and Puyuguapi Fjords had higher concentrations towards the surface, indicating elevated inputs in recent years. No major differences in metal content of the sediments were observed when compared with values from comparable natural systems in the northern hemisphere. Principal component analysis (PCA) grouped several seemingly isolated locations as having the same metal signature and indicated the pattern of dispersion across the region.
Assuntos
Monitoramento Ambiental/métodos , Sedimentos Geológicos/química , Metais/análise , Chile , Análise de Componente Principal , Espectrofotometria AtômicaRESUMO
A new method of determining the composition of sediment/soil gases and their volatile organic compound (VOC) content is described. VOCs were collected in situ from intertidal sediments in the Menai Strait and surrounding areas. The sampling was performed using a portable sampler comprising a funnel coupled to a SPME fibre. Gases were extracted from the sediments using a small vacuum pump pulling 100 mL min(-1) at atmospheric pressure. Sixty one different compounds were detected in the samples, and their fluxes and concentrations were determined. The compounds were classified into groups: halogenated, sulfur containing compounds, aldehydes, BTEXs (benzene, toluene, ethyl benzene and xylene) and aliphatic hydrocarbons. Results of principal component analysis (PCA) showed that the chemical composition of extracted gas was influenced primarily by sediment type. Muddy anoxic sediments were dominated by halogenated and sulfur containing compounds and sandy sediments had more aldehydes and BTEXs.
Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental , Sedimentos Geológicos/análise , Compostos Orgânicos/análise , Microextração em Fase Sólida , Aldeídos/análise , Derivados de Benzeno/análise , Cromatografia Gasosa-Espectrometria de Massas , Hidrocarbonetos Acíclicos/análise , Hidrocarbonetos Halogenados/análise , Compostos Orgânicos/química , Análise de Componente Principal , Compostos de Enxofre/análise , VolatilizaçãoRESUMO
Seasonal variation of antioxidant enzymes activities (superoxide dismutase, catalase, and glutathione peroxidases) and lipid peroxidation (LPO) were studied in the clam Ruditapes decussatus in relation to body burdens of polycyclic aromatic hydrocarbons (PAHs). Clams were sampled in eight sites from the Ria Formosa lagoon. PAH concentrations were seasonally rather than spatially dependent, being higher in summer (August). Antioxidant enzymes activities and LPO levels in the clam digestive gland were also seasonally dependent. Antioxidant enzymes presented distinct seasonal variations: Mit SOD (superoxide dismutase activity measured in the mitochondrial fraction) was induced in the summer and down-regulated in winter and spring, while Cyt SOD activity (measured in the cytosolic fraction) was highest in autumn and lower in the summer. Neither Mit nor Cyt SOD were related to the clam PAH body burden, suggesting that cells are using other antioxidant systems to eliminate oxyradicals. Catalase (CAT), however, was induced in spring and down-regulated in summer, the inverse of the PAH concentrations in clam tissues. CAT induction in spring appears to be related to the excess of oxyradicals arising from the metabolic activity associated with the reproductive cycle. Conversely, the decrease in CAT activity in the summer may be related to the high water temperatures reached in the Ria Formosa (up to 30 degrees C). Glutathione peroxidases (total fraction - T-GPx and dependent on selenium - Se-GPx) presented a similar seasonal pattern, and were negatively related to PAH concentrations, which may indicate a precarious state of the clams, associated with PAH toxicity. Similarly, LPO was also inversely correlated to the PAH concentrations indicating that increases in PAH concentrations were not causing membrane oxidative damage in R. decussatus digestive gland. The results suggest that antioxidant enzymes in R. decussatus digestive gland are strongly affected by seasonal factors stressing the need of other experiments to clarify the PAHs effect on this clam species.