Molecular biomarkers of oxidative stress in aquatic organisms in relation to toxic environmental pollutants

Effects of pesticides and antibiotics on penaeid shrimp with special emphases on behavioral and biomarker responses

The purpose of the present study is to provide information on the current state of knowledge regarding the effects of pesticides and antibiotics used in aquaculture on penaeid shrimp, one of the most common aquatic products for human consumption, with a special emphasis on the use of behavioral, physiological, and biochemical response. These include behavior; feeding rate changes; respiration rate, oxygen consumption, and osmoregulation alterations; nucleic acids, protein, and glycogen synthesis; cholinesterase activity inhibition; ATPase activity; and oxidative stress responses. This paper also deals with residues of antibiotics and pesticides in penaeid shrimp. Antibiotics and pesticides used in aquaculture may have adverse effects on treated animals and human consumers health if they are not correctly used. As a complement to the measurement of antibiotic and pesticide residues in tissues, the use of behavioral and biomarker responses can provide more relevant biological information on the potential adverse effects of antibiotics and pesticides on penaeid shrimp health.

Use of microarray technology to assess the time course of liver stress response after confinement exposure in gilthead sea bream (Sparus aurata L.)

Background

Selection programs for growth and stress traits in cultured fish are fundamental to the improvement of aquaculture production. The gilthead sea bream (Sparus aurata) is the main aquacultured species in the Mediterranean area and there is considerable interest in the genetic improvement of this species. With the aim of increasing the genomic resources in gilthead sea bream and identifying genes and mechanisms underlying the physiology of the stress response, we developed a cDNA microarray for gilthead sea bream that is enriched by suppression substractive hybridization with stress and immunorelevant genes. This microarray is used to analyze the dynamics of gilthead sea bream liver expression profile after confinement exposure.

Results

Groups of confined and control juvenile fish were sampled at 6, 24, 72 and 120 h post exposure. GeneSpring analyses identified 202 annotated genes that appeared differentially expressed at least at one sampling time (P < 0.05). Gene expression results were validated by quantitative PCR of 10 target genes, and K-means clustering of differently expressed genes identified four major temporal gene expression profiles. Set 1 encompassed a rapid metabolic readjustment with enhanced uptake and intracellular transport of fatty acids as metabolic fuels. Set 2 was associated with a wide variety of tissue repair and remodeling processes that were mostly mediated by the stress response of the endoplasmic reticulum (ER). Sets 3 and 4 encompassed the re-establishment of cellular homeostasis with increased intracellular trafficking and scavenging of reactive oxygen species (ROS), accompanied by a bidirectional regulation of the immune system and a general decline of ROS production.

Conclusions

Collectively, these findings show the complex nature of the adaptive stress response with a clear indication that the ER is an important control point for homeostatic adjustments. The study also identifies metabolic pathways which could be analyzed in greater detail to provide new insights regarding the transcriptional regulation of the stress response in fish.

NMR-based metabonomic study of the sub-acute toxicity of titanium dioxide nanoparticles in rats after oral administration

As titanium dioxide nanoparticles (TiO(2) NPs) are widely used commercially, their potential toxicity on human health has attracted particular attention. In the present study, the oral toxicological effects of TiO(2) NPs (dosed at 0.16, 0.4 and 1 g kg( - 1), respectively) were investigated using conventional approaches and metabonomic analysis in Wistar rats. Serum chemistry, hematology and histopathology examinations were performed. The urine and serum were investigated by (1)H nuclear magnetic resonance (NMR) using principal components and partial least squares discriminant analysis. The metabolic signature of urinalysis in TiO(2) NP-treated rats showed increases in the levels of taurine, citrate, hippurate, histidine, trimethylamine-N-oxide (TMAO), citrulline, alpha-ketoglutarate, phenylacetylglycine (PAG) and acetate; moreover, decreases in the levels of lactate, betaine, methionine, threonine, pyruvate, 3-D-hydroxybutyrate (3-D-HB), choline and leucine were observed. The metabonomics analysis of serum showed increases in TMAO, choline, creatine, phosphocholine and 3-D-HB as well as decreases in glutamine, pyruvate, glutamate, acetoacetate, glutathione and methionine after TiO(2) NP treatment. Aspartate aminotransferase (AST), creatine kinase (CK) and lactate dehydrogenase (LDH) were elevated and mitochondrial swelling in heart tissue was observed in TiO(2) NP-treated rats. These findings indicate that disturbances in energy and amino acid metabolism and the gut microflora environment may be attributable to the slight injury to the liver and heart caused by TiO(2) NPs. Moreover, the NMR-based metabolomic approach is a reliable and sensitive method to study the biochemical effects of nanomaterials.

Biomarkers of oxidative stress in the land snail, Theba pisana for assessing ecotoxicological effects of urban metal pollution

This study investigates the biomarkers of oxidative stress and heavy metal accumulation for assessing ecotoxicological effects of urban metal pollution in Alexandria city, Egypt. This investigation was performed in the digestive gland of roadside Theba pisana snails obtained from six different sites in the city. Relationships between heavy metal (Zn, Cu, Pb and Cd) concentrations and oxidative stress indicators were also examined. The results showed that mean concentrations of the measured elements (mugg(-1) dry weight) were higher in polluted sites when compared to the background levels of the reference site. The pattern of metals accumulation at all sites was Zn>Cu>Pb>Cd. In the metal polluted sites, snails displayed higher mean of catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities, lower reduced glutathione (GSH) content and higher levels of lipid peroxidation (LPO) compared to snails from the reference site. All oxidative stress parameters were positively correlated to heavy metal concentrations except GSH content which exhibits negative correlation with the concentrations of these metals. Our results suggest that the tested antioxidant defenses are sensitive parameters that could be useful as oxidative stress biomarkers in snails exposed to the actual metals in the environment. These biomarkers when complemented with metal accumulation in the digestive gland of snails may provide a powerful biomonitor for the assessment of environmental metal pollution.

Biomarkers and heavy metal bioaccumulation in mussels transplanted to coastal waters of the Beagle Channel

Mussels coming from a mussel farm at Brown Bay (Beagle Channel) were transplanted to four sites inside Ushuaia Bay for 2 and 4 weeks. The objective of this study was to assess the quality of coastal waters of Ushuaia Bay by measuring catalase activity, lipid peroxidation, total lipid content, bioaccumulation of heavy metals and condition index in transplanted mussel Mytilus edulis chilensis. Biomarkers except condition index showed significant differences among exposure times as well as among tissues. Digestive gland presented the highest catalase activity, malondialdehyde level and total lipid content. Digestive gland also was the main target tissue of accumulation of iron and copper, while gill accumulated the highest levels of zinc. A principal component analyzes with the whole set of data allowed to separate stations based on physicochemical conditions and biochemical responses of each studied area.

Sublethal effects of the organic antifoulant Mexel(R)432 on osmoregulation and xenobiotic detoxification in the flatfish Solea senegalensis

Mexel(R)432 is an anionic surfactant used as biocide in the cooling water system of power plants for biofouling reduction. Refrigeration waters from power plants do not usually follow, prior to their discharge to sea, any treatment aimed to eliminate biocides and this can have negative consequences on the aquatic fauna nearby. The effects of different concentrations of the antifoulant Mexel(R)432 (0.5, 1 and 2mgL(-1)) on osmoregulation (osmolality and Na(+)/K(+)-ATPase activity) and stress parameters (cortisol, glucose, and lactate) were assessed in juveniles of the flatfish Solea senegalensis. Gill histopathology and alterations due to oxidative stress (increased lipid peroxidation, LPO, levels) at branchial and hepatic levels were also considered. Other parameters tested were the antioxidant enzymes (catalase, CAT; glutathione peroxidase, GPX; and glutathione reductase, GR), xenobiotic metabolism defenses involved in detoxification (carboxylesterase, CbE; 7-ethoxyresorufin O-deethylase, EROD; and glutathione S-transferase, GST) and the neurotransmitter acetylcholinesterase (AChE) activity. Significant variations in osmoregulatory parameters, histological lesions and decreased branchial Na(+)/K(+)-ATPase activity were observed in exposed fish. Other gill biomarkers presented little or no significant variations in relation to controls. In contrast, hepatic parameters, such as CAT activity, were inhibited while EROD activity was initially elevated but after longer exposures it recovered basal values. These results suggested that under our experimental protocol exists toxic associated to Mexel(R)432 exposures.

Seasonal variations of the activity of antioxidant defense enzymes in the red mullet (Mullus barbatus l.) from the Adriatic Sea

This study investigated seasonal variations of antioxidant defense enzyme activities: total, manganese, copper zinc containing superoxide dismutase (Tot SOD, Mn SOD, CuZn SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and biotransformation phase II enzyme glutathione-S-transferase (GST) activity in the liver and white muscle of red mullet (Mullus barbatus). The investigations were performed in winter and spring at two localities: Near Bar (NB) and Estuary of the River Bojana (EB) in the Southern Adriatic Sea. At both sites, Mn SOD, GSH-Px, GR and GST activities decreased in the liver in spring. In the white muscle, activities of Mn SOD, GSH-Px, GR and GST in NB decreased in spring. GR decreased in spring in EB, while CAT activity was higher in spring at both sites. The results of Principal Component Analysis (PCA) based on correlations indicated a clear separation of various sampling periods for both investigated tissues and a marked difference between two seasons. Our study is the first report on antioxidant defense enzyme activities in the red mullet in the Southern Adriatic Sea. It indicates that seasonal variations of antioxidant defense enzyme activities should be used in further biomonitoring studies in fish species.

Oxidative stress response and gene expression with atrazine exposure in adult female zebrafish (Danio rerio)

Atrazine (ATZ) is the most common pesticide of freshwater ecosystems in the world. The effects of ATZ exposure on the induction of oxidative stress and the alteration of gene expression were studied in liver and ovary samples from female zebrafish (Danio rerio). Antioxidant enzyme activities (SOD and CAT), in addition to the GSH and MDA content, in the liver altered significantly; the mRNA levels for the genes encoding these antioxidant proteins, such as Cu/Zn-Sod, Mn-Sod, Cat, and Gpx, were up-regulated significantly in the liver when zebrafish were exposed to various concentrations of ATZ for 14d. However, the mRNA induction patterns were not in accordance with those of antioxidant enzyme changes in the liver and ovary. Moreover, the transcriptional expression of mitochondrial inner membrane genes related to ROS production, such as Ucp-2 and Bcl-2, were altered significantly in high ATZ treatment groups. However, the ATZ treatment did not induce any apparent changes in the transcriptional expression of CoxI, Ndi, or ATPo6, which are related to the mitochondrial respiratory chain and ATP synthesis. To our knowledge, this is the first report to study the transcriptional effects of ATZ stress on zebrafish. The information presented in this study will be helpful in fully understanding the mechanism of oxidative stress induced by ATZ in fish.

The effects of pollution on the vitamins A, E, C, beta-carotene contents and oxidative stress of the freshwater crayfish, Astacus leptodactylus

In this study, we determined the effects of pollution on levels of antioxidant vitamins (A, E, C), beta-carotene and malondialdehyde (MDA), in the hepatopancreas and muscle tissues of freshwater crayfish (Astacus leptodactylus). The crayfish samples were collected from Aydincik (unpolluted control site) and Ağin (polluted site) in the Keban Dam Lake (Elazig-Turkey) in August 2007. The results showed that the concentrations of vitamins E, C and beta-carotene in both tissues were significantly lower, and MDA levels were higher than in controls. There were no significant alterations in vitamin A levels. In comparison among the sex groups, some values were different significantly between the localities. The comparison of same-sex groups of the different localities also showed that concentrations of the vitamins E, C, beta-carotene and MDA changed statistically according to the tissues between the localities.

Effects of the model PAH phenanthrene on immune function and oxidative stress in the haemolymph of the temperate scallop Pecten maximus

Phenanthrene, a major component of crude oil, is one of the most abundant PAHs in aquatic ecosystems, and is readily bioavailable and toxic to a range of marine invertebrates. Within bivalves, the haemolymph acts as a transfer medium for these pollutants and their metabolic products, leaving haemocytes susceptible to deleterious effects. Using a suite of biological endpoints, this study determined the sublethal (7-d exposure to 50, 100 and 200microgL(-1)) effects of phenanthrene on several oxidative stress and immunological parameters in the haemolymph of the commercially-important scallop Pecten maximus. Phenanthrene exposure (200microgL(-1)) resulted in immune modulation with significant reductions in cell membrane stability (P<0.05) and phagocytosis (P<0.05), and a significant increase in the number of total haemocytes (P<0.05). Oxidative stress was also observed with a significant decrease in total glutathione (P<0.05) and significantly increased levels of lipid peroxidation in the haemolymph (P<0.05). Changes in the cellular and biochemical endpoints observed in this study illustrate their potential use in assessing the subtle effects of contaminant exposure. Whilst previous reports have suggested a link between free radical generation and immune suppression in vertebrates, this is the first instance where oxidative stress and immune function have been measured together in the haemolymph of a bivalve mollusc, demonstrating a possible link between PAH-induced oxidative stress and the subsequent inhibition in haemocyte immune function.

Muscular cholinesterase activities and lipid peroxidation levels as biomarkers in several Mediterranean marine fish species and their relationship with ecological variables

Muscular cholinesterase activities, as potential markers of neurotoxic exposure, and lipid peroxidation levels, indicative of oxidative stress damage, both currently used in early-warning pollution monitoring, were characterised in eighteen fish species of ecologic and/or economic importance. These species comprise five orders and eleven families of teleosts and two species of elasmobranchs, feed using different strategies (benthic, epibenthic, endobenthic and pelagic), belong to different trophic levels and express different swimming behaviour. Their habitat ranges from 50 to 60 m (shallow or continental shelf) and 600 to 850 m (middle continental slope). Sampling took place in front of the Barcelona coast (NW Mediterranean) during four seasonal cruises in 2007. In the summer sampling, another site potentially exposed to a different pollution load (Vilanova) was included for comparison. Species, seasonal and site differences were tested and discussed in relation to chemical analysis of the local sediment, systematic position, habitat depth, feeding strategy, trophic level and swimming activity. Greater inter species differences rather than seasonal or site trends were seen in accordance to little pollution fluctuations. Higher cholinesterase activities were recorded in suprabenthos feeders, regardless of depth habitat, whereas LP levels were similar in all species except for the shark Scyliorhinus canicula in which they were consistently elevated. This study confirms and broadens former observations carried out with a more reduced number of fish species (Solé et al., 2008a).

Modulation of antioxidant defence system in brain of rainbow trout (Oncorhynchus mykiss) after chronic carbamazepine treatment

We investigated the effect of long-term exposure to CBZ on the antioxidant system in brain tissue of rainbow trout. Fish were exposed to sublethal concentrations of CBZ (1.0 microg/L, 0.2mg/L or 2.0mg/L) for 7, 21, and 42 days. Oxidative stress indices (LPO and CP) and activities of antioxidant enzymes (SOD, CAT, GPx and GR) in fish brain were measured. In addition, non-enzymatic antioxidant (GSH) was determined after 42 days exposure. Carbamazepine exposure at 0.2mg/L led to significant increases (p<0.05) of LPO and CP after 42 days and, at 2.0mg/L, after 21 days. Activities of the antioxidant enzymes SOD, CAT, and GPx in CBZ-treated groups slightly increased during the first period (7 days). However, activities of all measured antioxidant enzymes were significantly inhibited (p<0.05) at 0.2mg/L exposure after 42 days and after 21 days at 2.0mg/L. After 42 days, the content of GSH in fish brain was significantly lower (p<0.05) in groups exposed to CBZ at 0.2mg/L and 2.0mg/L than in other groups. Prolonged exposure to CBZ resulted in excess reactive oxygen species formation, finally resulting in oxidative damage to lipids and proteins and inhibited antioxidant capacities in fish brain. In short, a low level of oxidative stress could induce the adaptive responses of antioxidant enzymes, but long-term exposure to CBZ could lead to serious oxidative damage in fish brain.

Diclofenac-enriched artificial sediment induces oxidative stress in Hyalella azteca

Diclofenac is a nonsteroidal anti-inflammatory drug widely used in Mexico where it is sold over the counter. It enters water bodies through municipal and industrial discharges, posing a risk to water systems and aquatic organisms. Diclofenac-enriched artificial sediment was used to evaluate the toxicity of this pharmaceutical on the sentinel species Hyalella azteca, using oxidative stress biomarkers in order to determine if the set of tests used in this study is a suitable early damage biomarker. The median lethal concentration (72-h LC(50)) was determined and oxidative stress was evaluated using lipid peroxidation, protein carbonyl content to evaluate oxidized protein content, and the activity of superoxide dismutase, catalase, and glutathione peroxidase. All biomarkers were significantly altered. Diclofenac induces oxidative stress in H. azteca and the set of tests used (lipid peroxidation, protein carbonyl content, antioxidant enzyme activities) constitutes an adequate early damage biomarker for evaluating the toxicity of this pharmaceutical group in aquatic species.

Levels of DNA adducts in the blood and follicular fluid of women undergoing in vitro fertilization treatment and its correlation with the pregnancy outcome

This study is designed to investigate the impact of DNA damage on pregnancy and fertilization rate outcome in a sub-sample of women undergoing IVF treatment. Blood and follicular fluid samples (n = 60) were analyzed for DNA adducts. While no BPDE-DNA adducts were detected, other unknown lipophilic adducts were seen in blood and follicular fluid. Women who failed to achieve pregnancy had higher DNA adducts in follicular fluid than those who succeeded (p < 0.05). Follicular fluid cotinine levels were associated with DNA adduct levels in blood and follicular fluid (p < 0.05). Evaluation of DNA damage resulting from oxidative stress could have a role in predicting IVF success rate.

Oxidative stress induced on Cyprinus carpio by contaminants present in the water and sediment of Madin Reservoir

Madin Reservoir (MR), located in the State of Mexico, is fed mainly by the Rio Tlalnepantla. MR supplies potable water to the municipalities of Naucalpan and Atizapan, and various recreational activities take place in its vicinity, such as sailing and the fishing of diverse species including the common carp Cyprinus carpio. The purpose of this study was to determine the toxic effects of contaminants present in MR water and sediment on C. carpio. Five sampling stations were selected (those considered to have the most problems due to discharges). Water and sediment samples were taken and toxicity studies were performed, including acute toxicity (lethality) and subacute toxicity assays. The biomarkers used in the subacute assays were lipid peroxidation (LPX) and activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in the liver and brain of test organisms. These biomarkers were also evaluated in local carp, i.e. carp with chronic exposure in situ to reservoir contaminants. Results show that contaminants in the water and sediment of the different sampling stations induce oxidative stress, this toxicity being more evident in samples from stations near the entry point of the Rio Tlalnepantla tributary and in local carp. This may be due to high contaminant levels as well as the fact that the physicochemical characteristics of the matrices might favor their bioavailability. Thus, both the water and sediment of this reservoir are contaminated with xenobiotics hazardous to C. carpio, a species consumed by the local human population.

Toxicological and ecotoxic impact of secondary and tertiary treated sewage effluents

Secondary sewage effluents are discharged in significant quantities in aquatic environments delivering pollutants that were not removed during treatment; yet advanced treated effluents are not lacking of contaminants. In this study, biochemical biomarkers were measured in liver and kidney of rainbow trout (Oncorynchus mykiss) exposed to unchlorinated, chlorinated and tertiary treated secondary sewage effluents. In addition, organic matter, nitrogen and suspended solids were assayed, while a common bioassay, Daphnia magna 21d reproduction test was also applied in order to examine potential relation between the performed bioassay and the biomarkers. Processes using oxidative conditions, such as ozonation and chlorination, resulted in significantly increased breeding rate (up to 74%) of the organism. Biomarkers measurements incorporated the determination of total glutathione (GSH), glutathione S-transferases (GST), glutathione peroxidase (GPX), lipid peroxidation (LPO) and an innovative biomarker in such applications, haem peroxidase. In general, the response of biomarkers was dependent upon the treatment method and it was tissue specific. Secondary effluents inhibited liver GST and haem peroxidase, while GSH levels and LPO were significantly provoked in liver. Ozonation provoked hepatic peroxidation, in terms of haem peroxidase and LPO, and GST; while the protective (to Reactive Oxidant Species - ROS) GSH was depleted, suggesting extended ROS attack to the organism. Similar response of biomarkers (but to a lesser extend) was observed after exposure of trout to effluents submitted to both coagulation and ozonation, emphasizing the significance of removing the residual organic matter by other methods than oxidative ones. Ozonation also enhanced renal LPO and GPX; however the former employment of coagulation limited the peroxidation phenomena. Chlorination mainly affected the levels of total GSH in both tissues.

Malathion-induced alteration of the antioxidant defence system in kidney, gill, and intestine of Carassius auratus gibelio

Pesticides such as malathion, commonly used in agriculture and households, are toxic substances that lead to reactive oxygen species generation, which harms organisms. Ecotoxicological consequences of malathion, particularly its effects on antioxidants in fish, are not well understood. Thus, we investigated the effects of malathion (0.05 mg/L) on lipid peroxidation and antioxidant systems in Carassius auratus gibelio kidney, intestine, and gills following exposure times of 1, 2, 3, and 6 days. The lipid peroxidation and antioxidative defense mechanisms display different responses in investigated tissues. The lipid peroxidation was increased in all investigated tissues, especially after 1 day of malathion administration. Changes in reduced glutathione levels have been registered, mainly after 6 days of pesticide exposure. The modulation in the activities of antioxidant enzymes, catalase, gluthatione peroxidase, glutathione reductase, and glutathione-S-transferase was time and tissue specific. The investigated parameters can be used as biomarkers of fish exposure to malathion.

Toxicological responses in wheat Triticum aestivum under joint stress of chlorimuron-ethyl and copper

It was observed in this work that joint effects of chlorimuron-ethyl and copper on chlorophyll content, the peroxidases (POD) activity, superoxide dismutases (SOD) activity and soluble protein content in leaves and roots of wheat were markedly significant. The chlorophyll content and the SOD activity in wheat under joint stress of chlorimuron-ethyl and copper were obviously higher than that under single stress of chlorimuron-ethyl. However, joint effect of chlorimuron-ethyl and copper on the decrease of soluble protein content in roots was more serious than that under single stress of chlorimuron-ethyl. The effect of copper dominated the change of POD activity and soluble content in leaves and roots of wheat under joint stress of chlorimuron-ethyl and copper. It was suggested that the change of enzyme activity was related to the change of soluble protein content in roots under single and joint stress of chlorimuron-ethyl and copper.

Joint stress of copper and petroleum hydrocarbons on the polychaete Perinereis aibuhitensis at biochemical levels

Responses of the polychaete Perinereis aibuhitensis Grube to single and joint stress of copper (Cu) and petroleum hydrocarbons (PHCs) at biochemical levels (including superoxide dismutases, SOD; peroxidases, POD; and the content of total soluble protein, TSP) were investigated under controlled laboratorial conditions. Significant decreases in SOD activity in the first 3 days of single exposure to Cu or PHCs were observed. Although SOD activity increased and returned to the level of the control on day 6 after having decreased on day 3 under single stress of Cu or PHCs, Cu and PHCs had complicated interactive influences on SOD activity in P. aibuhitensis. Their joint effects on SOD activity depended on concentration combinations and exposure time, called double-dose dependent effects. The POD activity and the content of TSP remained generally constant under both single and joint stress of Cu and/or PHCs, compared with the control. The beef-witted responses of investigated biochemical parameters in this study might suggest that toxic effects of pollutants with emphasis on the action of abiotic parameters and the time factor on the antioxidant enzymes in the polychaete should be addressed in the future work.

Genomic organization and mRNA expression of manganese superoxide dismutase (Mn-SOD) from Hemibarbus mylodon (Teleostei, Cypriniformes)

The genomic structure of manganese superoxide dismutase (Mn-SOD) was characterized in Hemibarbus mylodon (Teleostei, Cypriniformes), an endangered freshwater fish species, and changes in Mn-SOD mRNA expression in response to various stimuli, such as challenge with lipopolysaccharide (LPS), bacteria, or heavy metals, were examined. H. mylodon Mn-SOD possesses well-conserved features of vertebrate Mn-SODs, including its homologous quinquepartite gene structure (five exons interrupted by four introns) and high sequence identity with vertebrate orthologs in coding regions, including a typical eukaryotic Mn-SOD signature. The 5'-regulatory upstream region of the H. mylodon Mn-SOD gene lacked a canonical TATA sequence; however, it displayed various transcription factor binding elements that may be involved in immune and stress responses, as well as the modulation of enzymes that mediate the metabolism of metals and other xenobiotics. Bioinformatic analysis of Mn-SOD genes from fish and mammalian genome databases revealed chromosomal synteny of the Mn-SOD locus in the vertebrate lineage. Mn-SOD transcripts were ubiquitously detected in diverse tissues with variable levels of basal expression using an RT-PCR assay. Mn-SOD expression in the liver and kidney were significantly modulated by injection of LPS (1, 5, or 10 microg g(-1) body weight), Edwardsiella tarda challenge (5 x 10(3) or 5 x 10(5) cells/fish), and heavy metal exposure (Cd, Cu, or Zn at 5 microM). Results from this study suggest that Mn-SOD plays an important role in the host defence against oxidative damage caused by infection-mediated inflammation and/or toxicant related stress in this species.

Biotransformation and antioxidant enzymes of Limnoperna fortunei detect site impact in watercourses of Córdoba, Argentina

The golden mussel Limnoperna fortunei was used as a biomonitor of environmental pollution in the Suquía River basin around Córdoba City (Argentina). The sampling sites along the river were chosen according to their increasing levels of pollutants (e.g. heavy metals) as well as biological oxygen demand (BOD) and chemical oxygen demand (COD). A water quality index (WQI) was constructed from the interaction of several normalized factors that affect the aquatic environment, such as the mentioned pollutants and physico-chemical characteristics of the sampling sites. Activity changes of biotransformation enzyme glutathione S-transferase (GST) and the antioxidant enzymes glutathione peroxidase (GPx), glutathione reductase (GR) and catalase (CAT), after exposure to pollutants, served as biomarkers. Membrane bound GST and antioxidant enzymes responded at the most polluted sampling site within 1 day showing increased activities lasting for 4 days. Further sampling was restricted due to no survival of the animals. Antioxidant enzymes GPx, GR and CAT were sensitive responding to the different pollution scenarios, showing good correlation to the chemical characterization.

A multi-biomarker assessment of the impact of the antibacterial trimethoprim on the non-target organism Zebra mussel (Dreissena polymorpha)

A battery of eight biomarkers was applied in the freshwater mussel Dreissena polymorpha to evaluate potential sub-lethal effects of the antimicrobial trimethoprim (TMP, 5-[3,4,5-trimethoxybenzyl]pyrimidine-2,4-diamine). Mussels were exposed for 96 h to increasing concentrations (1, 3, 10 nM) of TMP in in vivo experiments. We determined the single cell gel electrophoresis (SCGE) assay, the micronucleus test (MN test), the apoptotic frequency (Halo assay) and the lysosomal membrane stability (Neutral Red Retention Assay) in mussel hemocytes. Moreover, to reveal whether the oxidative status was altered, measurements of the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and the phase II detoxifying enzyme glutathione S-transferase (GST) were performed using the cytosolic fraction extracted from a pool of entire mussels. The biomarker battery pointed out only a moderate cyto- and genotoxicity on Zebra mussel hemocytes since only a slight increase in DNA damage was registered by apoptosis induction and MN frequency, while significant differences of lysosomal membrane stability from baseline levels were measured at 3 and 10 nM at the end of exposures only. Finally, TMP seems to have a very low induction capability or even an inhibitory effect on the activities of antioxidant enzymes, but a clear significant induction on GST.

Multi-level ecotoxicity assay on the aquatic midge, Chironomus tentans (Diptera, Chironomidae) exposed to octachlorostyrene

Octachlorostyrene (OCS) is a ubiquitously distributed compound, of which, ecotoxicological property is little known. To investigate the ecotoxicity of OCS, short- and long-term experiments were conducted under controlled laboratory conditions, using the aquatic midge, Chironomus tentans, as a biological model system. Ecophysiological responses using organism/population level endpoints, such as growth, reproduction and development, were investigated. Moreover, oxidative stress-related parameters and the expression of heat shock protein and hemoglobin gene were also investigated as potential biomarkers for OCS exposure. Significant disturbance in male/female adult ratio and on oviposition by chronic exposure to OCS suggests that this compound may have serious consequences on Chironomus population by affecting reproduction. To elucidate the mechanism of these speculated phenomena, direct experimental demonstrations on the relationships between observed ecotoxicological response and upstream-induced molecular/biochemical events may be needed.

Prometryne-induced oxidative stress and impact on antioxidant enzymes in wheat

Prometryne is one of the herbicides widely used for controlling weed/grass in agricultural practice. However, whether it has an adverse effect on crops is unknown. In this study, we investigated prometryne-induced oxidative stress in wheat (Triticum aestivum). Wheat plants were grown in soils with prometryne at 0-24 mgkg(-1) soil. The growth of wheat treated with prometryne was inhibited. Chlorophyll content significantly decreased even at the low level of prometryne (4 mgkg(-1) soil). Accumulation of thiobarbituric acid reactive substances (TBARS), an indicator of cellular peroxidation, increased, suggesting oxidative damage to the plants. The prometryne-induced oxidative stress triggered significant changes in activities of a variety of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione S-transferase (GST). Activities of the enzymes showed a general increase at low prometryne concentrations but a decrease at high levels. Analysis of non-denaturing polyacrylamide gel electrophoresis (PAGE) confirmed the results. To get an insight into the molecular response, a qRT-PCR-based assay was performed to analyze the transcript abundance of Cu/Zn-SOD and GST with prometryne exposure. Our analysis revealed that both genes displayed up-regulated expression patterns similar to the activities of the two enzymes. These data imply that prometryne-induced oxidative stress was responsible for the disturbance of the growth and antioxidant defensive systems in wheat plants.

Assessing the toxicity of TBBPA and HBCD by zebrafish embryo toxicity assay and biomarker analysis

Tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) are two of the most widely used brominated flame retardants (BFRs). The biological toxicity effect of TBBPA and HBCD was studied by means of zebrafish embryo toxicity assays in combination with three biomarkers, including superoxide dismutase (SOD), lipid peroxidation, (LPO), and heat shock protein (Hsp70). The standard zebrafish embryo assay showed that high concentrations of TBBPA (> or =0.75 mg/L) can cause lethality or malformation. For HBCD within the concentration range (0.002-10 mg/L), no endpoint was observed. Furthermore, SOD activities of zebrafish embryos exposed to TBBPA were increased with the increasing concentrations. SOD activities in the group treated by HBCD showed an increase followed by a decline. Regardless of TBBPA or HBCD, LPO were increased along with the increase of the concentration. The change pattern of Hsp70 levels was the same with LPO. All these results showed that TBBPA and HBCD could cause oxidative stress and Hsp70 overexpression, inducing acute toxicity to zebrafish embryo in a short-term exposure. The study also indicates that the zebrafish embryo assay in combination with the biomarkers is effective in aquatic environmental toxicology and risk assessment.

Low toxic herbicide Roundup induces mild oxidative stress in goldfish tissues

The formulation of Roundup consists of the herbicide glyphosate as the active ingredient with polyethoxylene amine added as a surfactant. The acute toxicity of Roundup (particularly of glyphosate) to animals is considered to be low according to the World Health Organization, but the extensive use of Roundup may still cause environmental problems with negative impact on wildlife, particularly in an aquatic environment where chemicals may persist for a long time. Therefore, we studied the effects of Roundup on markers of oxidative stress and antioxidant defense in goldfish, Carassius auratus. The fish were given 96 h exposure to Roundup at concentrations of 2.5-20 mg L(-1). Exposure to Roundup did not affect levels of lipid peroxides (LOOH) in goldfish brain or liver, and in kidney only the 10 mg L(-1) treatment elevated LOOH by 3.2-fold. Herbicide exposure also had no effect on the concentrations of protein thiols or low molecular mass thiols in kidney, but selective suppression of low molecular mass thiols by 26-29% occurred at some treatment levels in brain and liver. Roundup exposure generally suppressed the activities of superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione reductase and glucose-6-phosphate dehydrogenase in fish tissues. For example, SOD activities were reduced by 51-68% in brain, 58-67% in liver and 33-53% in kidney of Roundup treated fish. GST activity decreased by 29-34% in liver. However, catalase activity increased in both liver and kidney of herbicide-exposed fish. To our knowledge this is the first study to demonstrate a systematic response by the antioxidant systems of fish to Roundup exposure.

Immunologic parameters evaluations in Nile tilapia (Oreochromis niloticus) exposed to sublethal concentrations of diazinon

Fish resistance to microorganisms depends basically on the immune response. Although there are several studies on the diazinon mammalian immunotoxicity, in the case of fish there are only few. The aim of present study was to evaluate the effect of diazinon on immunological parameters (relative spleen weight, splenocytes count, lysozyme activity, respiratory burst and IgM concentration) in Nile tilapia. Diazinon at sublethal concentrations (0.39 and 0.78 mg/L) did not alter RSW, splenocytes count or lysozyme activity. However, at the highest concentration tested (1.96 mg/L) diazinon significantly increased respiratory burst and IgM concentration. In summary, diazinon (and perhaps other pesticides) could alter immunological response and induce oxidative stress.

Characterisation of integrated stress biomarkers in two deep-sea crustaceans, Aristeus antennatus and Nephrops norvegicus, from the NW fishing grounds of the Mediterranean sea

Several biomarkers indicative of stress were characterised in the crustaceans Aristeus antennatus and Nephrops norvegicus sampled off the Barcelona coast (NW Mediterranean). The biomarkers selected were cholinesterase (ChE) activities in muscle; and catalase, glutathione reductase (GR), total glutathione peroxidase (t-GPX), DT-diaphorase (DT-D), glutathione S-transferases (GSTs) and carboxylesterases (CbEs) in hepatopancreas tissue. Lipid peroxidation (LP) levels and total protein yield (PY) were also determined in muscle and hepatopancreas tissues. The activities and levels are discussed in relation to species and season, and differences in these two factors were observed for most biomarkers. AChEs and pseudocholinesterases were present in the muscles of both crustaceans. Catalase and GST activities were higher in N. norvegicus, whereas GR and t-GPX activities varied according to the season. Hepatic CbE activities were similar in the two crustaceans, whereas LP levels and PY were different between species. Seasonality and species particularities are factors to consider when these crustaceans are used as sentinels.

Effects of cadmium on respiratory burst, intracellular Ca2+ and DNA damage in the white shrimp Litopenaeus vannamei

Acute effects of heavy metal ions on shrimp have been an area of intense study worldwide. However, the molecular mechanism by which cadmium-induced injury occurs remains largely unclear, and methods for mitigating toxicity in vivo have rarely been reported. In this study, the changes in respiratory burst and intracellular free calcium in haemocytes of pacific white shrimp, Litopenaeus vannamei, after exposure to Cd(2+) (CdCl(2)) were examined using flow cytometry. Meanwhile, DNA damage and repair in haemocytes and hepatopancreas cells were studied using the comet assay. Respiratory burst generation, intracellular Ca(2+) concentration ([Ca(2+)]i) and DNA damage in haemocytes and hepatopancreas cells all exhibited a dose-dependent increase and a time-dependent change after treatment with Cd(2+) compared with controls. These results indicate that Cd can induce oxidative stress and DNA damage in the shrimp L. vannamei. Moreover, the results also demonstrate that these parameters can be used as sensitive indicators of exposure to this genotoxicant.

Genotoxicity of heptachlor and heptachlor epoxide in human TK6 lymphoblastoid cells

The genotoxic potential of the organochlorine insecticides heptachlor (HC) and its metabolite heptachlor epoxide (HCE) has been evaluated in TK6 cells, a well-established human lymphoblastoid cell line. Genotoxicity has been determined by scoring the induction of DNA breaks in the comet assay and by measuring the frequency of micronuclei (MN) in binucleated cells. The results indicate that both compounds are able to induce significant increases in the percentage of DNA in the tail, the parameter used in the comet assay, with a direct dose-response relationship. Nevertheless, both compounds were unable to induce an increase in the frequency of MN. The comet assay measures primary DNA damage, while the induction of MN measures fixed damage. Thus, our results would suggest that the DNA damage induced by the two insecticides is not fixed as chromosome damage, which would be detectable by means of the MN assay (chromosome breaks and aneuploidy).

A method to measure total antioxidant capacity against peroxyl radicals in aquatic organisms: application to evaluate microcystins toxicity

Determination of total antioxidant capacity, instead of the measurements of limited number of antioxidants, is very important for the understanding of how antioxidants interact with reactive oxygen species (ROS). Several techniques already exist with this propose, although some of them are extremely time-consuming. A new methodology is proposed, based on the detection of ROS by fluorometry (ex/em: 485/520 nm) employing 2',7'-dichlorofluorescein diacetate (H(2)DCF-DA) as substrate. Supernatant of homogenized samples from different organs (gill, muscle, liver, and brain) of the teleost fish Jenynsia multidentata (Anaplebidae) were exposed to peroxyl radicals generated by thermal (35 degrees C) decomposition of 2,2'-azobis (2 methylpropionamidine) dihydrochloride (ABAP, 4 mM). Different protein concentrations (0.5, 1, 2 and 8 mg/ml) were assayed to get the best signal and curve fitting of fluorescence data over time (30 min). Total antioxidant capacity against peroxyl radicals was estimated as the difference in ROS area with and without ABAP, relative to the fluorescence registered without ABAP. For application of this methodology, J. multidentata specimens were exposed for 24 h to microcystins, cyanotoxins known to induce oxidative stress. Almost all organs showed a lower antioxidant capacity (p<0.05) in samples with 8 mg proteins/ml, when compared to protein content of 1-2 mg/ml. In liver samples, higher (p<0.05) free iron content was determined in samples with 8 mg proteins/ml. Sensitivity test employing GSH spiked in homogenized samples showed the protocol efficiency in detecting total antioxidant capacity. In the test with microcystins a dose-dependent decrease (p<0.05) of antioxidant competence in gills and brain and an inverse result with liver samples were observed. The use of antioxidant defenses was efficient in avoiding oxidative damage, as the content of oxidized proteins was not altered. Data obtained show the potential of this new methodology to be used in ecotoxicological studies.

Oxidative stress responses in bivalves (Scrobicularia plana, Cerastoderma edule) from the Oued Souss estuary (Morocco)

The aim of this work was to study the responses of oxidative-stress biomarkers (catalase: CAT, thiobarbituric acid reactive substances: TBARS) in bivalves (Scrobicularia plana and Cerastoderma edule) from the Oued Souss estuary (Morocco). This estuary, subjected to large amounts of sewage discharges and industrial effluents, do not receive since November 2002 any waste outlets due to their connection to a wastewater purification plant. High CAT and TBARS values were recorded in both species collected before the implantation of wastewater treatment. These results confirm that these bivalves were submitted to various contaminants generating oxidative stress and membrane lipid peroxidation. The diminution of these two biomarkers following the setting up of the purification plant indicates probably a reduction in contaminants in the Oued Souss estuary. We recommend the use of CAT and TBARS as oxidative-stress biomarkers in S. plana and C. edule.

Effect of broccoli (Brassica oleracea) and its phytochemical sulforaphane in balanced diets on the detoxification enzymes levels of tilapia (Oreochromis niloticus) exposed to a carcinogenic and mutagenic pollutant

Tilapia fish (Oreochromis niloticus) were fed with enriched diets containing broccoli and its phytochemical sulforaphane over 30 d. The levels of cytochrome P450, superoxide dismutase, catalase, lipid peroxidation and glutathione-S-transferase activities were measured. Basal value of cytochrome P450 activity was significantly increased as consequence of the broccoli and sulforaphane enriched diets, while no statistically significant changes were found on catalase and lipid peroxidation activities. After benzo(a)pyrene exposure, the cytochrome P450 activity increased to higher levels in the fish feed with broccoli and sulforaphane when compared with the control fish. Activities of antioxidant enzymes also varied but without significant difference with the control fish. Supported by the lower concentrations of BaP metabolites in bile from fish fed with broccoli or with sulforaphane enriched diets (indicating a better xenobiotic elimination) the cytochrome P450 induction could be considered beneficial for the detoxification because this transformation is the first step for PAH elimination by the phase II system. The protection of aquaculture organism against pollution effects by designing special diets able to modulate the enzymes involved in the phase-I and phase-II detoxification mechanism are discussed.

Antioxidant responses and NRF2 in synergistic developmental toxicity of PAHs in zebrafish

Early piscine life stages are sensitive to polycyclic aromatic hydrocarbon (PAH) exposure, which can cause pericardial effusion and craniofacial malformations. We previously reported that certain combinations of PAHs cause synergistic developmental toxicity, as observed with coexposure to the aryl hydrocarbon receptor agonist beta-naphthoflavone (BNF) and cytochrome P4501A inhibitor alpha-naphthoflavone (ANF). Herein, we hypothesized that oxidative stress is a component of this toxicity. We examined induction of antioxidant genes in zebrafish embryos (Danio rerio) exposed to BNF or ANF individually, a BNF + ANF combination, and a prooxidant positive control, tert-butylhydroperoxide (tBOOH). We measured total glutathione (GSH) and attempted to modulate deformities using the GSH synthesis inhibitor L-buthionine (S,R)-sulfoximine (BSO) and increase GSH pools with N-acetyl cysteine (NAC). In addition, we used a morpholino to knockdown expression of the antioxidant response element transcription factor NRF2 to determine if this would alter gene expression or increase deformity severity. BNF + ANF coexposure significantly increased expressions of superoxide dismutase 1 and 2, glutathione peroxidase 1, pi class glutathione-s-transferase, and glutamate cysteine-ligase to a greater extent than tBOOH, BNF, or ANF alone. BSO pretreatment decreased some GSH levels, but did not worsen deformities, nor did NAC diminish toxicity. Knockdown of NRF2 increased mortality following tBOOH challenge, prevented significant upregulation of antioxidant genes following both tBOOH and BNF + ANF exposures, and exacerbated BNF + ANF-related deformities. Collectively, these findings demonstrate that antioxidant responses are a component of PAH synergistic developmental toxicity and that NRF2 is protective against prooxidant and PAH challenges during development.

Oxidative stress and structure-activity relationship in the zebrafish (Danio rerio) under exposure to paclobutrazol

The acute toxicity and changes in the activity of antioxidant enzymes including superoxide dismutase (SOD) and catalase (CAT) in the zebrafish Danio rerio were measured when the fish was exposed to paclobutrazol (PBZ) under laboratory conditions. The median lethal concentration value at 96 h post-exposure (LC(50) (96 h)) was determined to be 20.55 mg/L. In addition, the SOD activities in D. rerio were significantly higher at 96 h post-exposure among the various concentrations of the pollutant tested. The change of CAT activity could be considered as a sensitive biomarker of the oxidative stress induced by PBZ. The structure-activity relationship (SAR) analysis identified the potential active points for the pollutant and that the cavum may be the site of interaction with the receptor.

The effects of selenium on oxidative stress biomarkers in the freshwater characid fish matrinxã, Brycon cephalus (Günther, 1869) exposed to organophosphate insecticide Folisuper 600 BR (methyl parathion)

Methyl parathion (MP), an organophosphate widely applied in agriculture and aquaculture, induces oxidative stress due to free radical generation and changes in the antioxidant defense system. The antioxidant roles of selenium (Se) were evaluated in Brycon cephalus exposed to 2 mg L(-1) of Folisuper 600 BR (MP commercial formulation - MPc, 600 g L(-1)) for 96 h. Catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione S-transferase (GST), reduced glutathione (GSH) and lipid peroxidation (LPO) levels in the gills, white muscle and liver were evaluated in fish fed on diets containing 0 or 1.5 mg Se kg(-1) for 8 weeks. In fish treated with a Se-free diet, the MPc exposure increased SOD and CAT activities in all tissues. However, the GPx activity decreased in white muscle and gills whereas no alterations were observed in the liver. MPc also increased GST activity in all tissues with a concurrent decrease in GSH levels. LPO values increased in white muscle and gills and did not change in liver after MPc exposure. A Se-supplemented diet reversed these findings, preventing increases in LPO levels and concurrent decreases in GPx activity in gills and white muscle. Similarly, GSH levels were maintained in all tissue after MPc exposure. These results suggest that dietary Se supplementation protects cells against MPc-induced oxidative stress.

Xenobiotic metabolism markers in marine fish with different trophic strategies and their relationship to ecological variables

Nine fish species of commercial interest from six teleost families and two species of elasmobranchs were selected for characterisation of hepatic biomarkers used in early-warning assessment of pollutant exposure. The sampling was carried out in front of the Barcelona coast (NW Mediterranean) during December 2006 at shelf (53 m) and slope (660 m) depths. The enzymes considered included the antioxidant defence catalase (CAT) and glutathione reductase (GR), phase I ethoxyresorufin O-deethylase (EROD) and phase II glutathione S-transferase (GST). Protein yield (PY) was used as a general marker of hepatic protein synthesis. Significant interspecies differences were evidenced, although each marker varied independently. Enzymatic activities in teleosts were higher than in elasmobranchs; they were very low in Scyliorhinus canicula (mainly a benthic feeder), but not so low in Galeus melastomus (pelagic feeder). In relation to depth, shallow water, shelf-living species had higher metabolic activities. Trophic variables were significantly related to PY and EROD activity, and were especially high in benthic/suprabenthic feeders. Trophic level (deduced from stable isotopy) and stomach fullness were associated with all hepatic markers, except GR. Swimming capacity was related to all hepatic enzymes. Our findings can be applied, not only from the perspective of conservation ecology regarding pollution, but also in fisheries, due to the economic interest of the species involved.

Multivariate discriminant analysis distinguishes metal- from non metal-related biomarker responses in the clam Chamaelea gallina

Molecular biomarkers are among the most sensitive and earliest responses to pollutants. However, lack of detailed knowledge on variability of responses and their possible seasonal variation limit their use. In addition, the seasonality of biological processes modulates the response of organisms to pollutant stressors. Using multivariate statistics, we have studied the influence of environmental and biological factors on the response of a battery of molecular biomarkers in the clam Chamaelea gallina collected along the South-Spanish littoral. Multivariate discriminant analysis clearly distinguished biomarker response between clean and polluted areas, using heavy metals as indicator of pollution. Such differences disappeared when the dataset was normalised for metal content, thus indicating that pollution was the main significant cause of the changes observed between clean and polluted sites. In conclusion, this work shows that, when applying a complete biomarker panel, multivariate statistical tools can be used to discern pollutant- from non pollutant-related responses.

Enhancement of hypoxia-induced gene expression in fish liver by the aryl hydrocarbon receptor (AhR) ligand, benzo[a]pyrene (BaP)

Fish in polluted coastal habitats commonly suffer simultaneous exposure to both hypoxia and xenobiotics. Although the adaptive molecular responses to each stress have been described, little is known about the interaction between the signaling pathways mediating these responses. Previous studies in mammalian hepatoma cell lines have shown that hypoxia-inducible factor (HIF)- and/or aryl hydrocarbon receptor (AhR)-activated gene expression is suppressed following co-exposure to hypoxia and the hallmark AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). However, whether similar crosstalk exists in the non-tumor liver tissues of fish and whether other non-TCDD ligands also play the same inhibitory role in this crosstalk remain unknown. Here, the in vivo hepatic mRNA expression profiles of multiple hypoxia- and AhR-responsive genes (later gene expression=mRNA expression of the gene) were examined in the orange-spotted grouper (Epinephelus coioides) upon single and combined exposures to hypoxia and benzo[a]pyrene (BaP). Combined exposure enhanced hypoxia-induced gene expression but did not significantly alter BaP-induced gene expression. Protein carbonyl content was markedly elevated in fish subjected to combined exposure, indicating accumulation of reactive oxygen species (ROS). Application of diethyldithiocarbamate (DDC) to hypoxia-treated grouper liver explants similarly exaggerated hypoxia-induced gene expression as in the combined stress tissues in vivo. These observations suggest that ROS derived from the combined hypoxia and BaP stress have a role in enhancing hypoxia-induced gene expression.

Photo-induced toxicity of four polycyclic aromatic hydrocarbons, singly and in combination, to the marine diatom Phaeodactylum tricornutum

Polycyclic aromatic hydrocarbons (PAHs) enter the aquatic environment by various routes and are usually found as mixtures in the water. Many studies have shown that solar ultraviolet (UV) radiation can greatly enhance the toxicity of some PAHs to a variety of marine species. In the present study, we tested the phototoxicity of four PAHs with simple structures, both alone and in binary combinations, to a species of marine diatom, Phaeodactylum tricornutum, in the laboratory. The results indicated that simulated solar UV radiation not only enhanced the toxicity of the different PAHs to this alga, but also changed their relative toxic strengths. The photo-induced toxicity of PAHs to this alga might be a synergistic effect of photo-modification and photosensitization reactions, causing the microalgal cells to suffer oxidative stress. Four binary mixtures of these PAHs were found to have a synergistic joint action mode, while two binary mixtures displayed an antagonistic reaction, revealing a complex pattern of possible interactions of PAHs with marine diatoms.