Laboratory measurements of biomarkers and individual performances in Chironomus xanthus to evaluate pesticide contamination of sediments in a river of southeastern Brazil

Ecotoxicological strategies employing biochemical markers and organisms to monitor the efficacy of malathion photolysis treatment

The objective of this study was to assess the photolysis-mediated degradation of malathion in standard and commercial formulations, and to determine the toxicity of these degraded formulations. Degradation tests were carried out with 500 μg L-1 of malathion and repeated three times. The initial and residual toxicity was assessed by using Lactuca sativa seeds for phytotoxicity, Stegomyia aegypti larvae for acute toxicity, and Stegomyia aegypti mosquitoes (cultivated from the larval stage until emergence as mosquitoes) to evaluate the biochemical markers of sublethal concentrations. For the standard formulations the photolytic process efficiently reduced the initial concentration of malathion to levels below the regulatory limits however, the formation of byproducts was revealed by chromatography, which allowed for a more complete proposal of photolytic-mediated malathion degradation route. The degraded formulations inhibited the growth of L. sativa seeds, while only the untreated formulations showed larvicidal activity and mortality. Both formulations slightly inhibited acetylcholinesterase activity in S. aegypti mosquitoes, while the standard formulation decreased and the commercial formulation increased glutathione S-transferase activity. However, there were no significant differences for superoxide dismutase, esterase-α, esterase-β and lipid peroxidation. These findings indicate that in the absence of the target compound, the presence of byproducts can alter the enzymatic activity. In general, photolysis effectively degrade malathion lower than the legislation values; however, longer treatment times must be evaluated for the commercial formulation.

Chironomus sancticaroli (Diptera: Chironomidae) in ecotoxicology: laboratory cultures and tests

Chironomus sancticaroli is a tropical species, easy to grow and to maintain in laboratory cultures. It has a fast reproduction cycle, under adequate conditions, around 30 days, allowing it to have many generations per year, an important criterion for selecting a test organism in ecotoxicology. Its life stages include: eggs, four larval instars (one planktonic and three benthic), pupa and adult (midges) This study aimed to: (1) review the methods for C. sancticaroli cultivation and its use in ecotoxicological tests, (2) establish a laboratory culture of C. sancticaroli, presenting the difficulties and discussing the ways to overcome them. Early 4th instar larvae was the most used in acute studies, while the 1st instar larvae (early 1st instar) was the most used in chronic studies; 96 h and 28 days were the most frequent durations in acute and chronic studies, respectively. The most common endpoints evaluated were organisms' survival and development, and most of the ecotoxicological studies using C. sancticaroli were performed in laboratory. Most of the tested contaminants were pesticides and these had the most adverse effects on organisms. Most mesocosms with environmental contaminated samples did not show adverse effects on C. sancticaroli. Chronic and field studies as well as those testing the effects of the mixture contaminants on C. sancticaroli were still deficient. Keeping the laboratory environment and equipment effectively sanitized was important as well as maintaining stabilized conditions of temperature, photoperiod, physical, chemical and biological water quality in cultures.

Bio-functionalized zinc oxide nanoparticles: Potential toxicity impact on freshwater fish Cyprinus carpio

There is a growing concern nowadays over the exposure of nanomaterials and their effects in aquatic life. In spite of reporting the changes in physiology, reproduction and behaviour in fish by different nanoparticles, the molecular events underlying in the aquatic bodies due to the toxicity of zinc oxide nanoparticles (ZnO NPs) are mainly unexplored. Therefore, the present study carried out an ex vivo exposure of ZnO NPs at various concentrations (0.382, 0.573 and 1.146 mg L^-1) in freshwater fish Cyprinus carpio to investigate the potential adverse effects. The results revealed that ZnO NPs exposure altered the haematological parameter and induces the reactive oxygen species (ROS) that leads to elevation of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidise (GPx), glutathione S-transferase (GST) and reduced glutathione (GSH) activity in C. carpio. Furthermore, histopathological analysis exhibited that the ZnO NPs caused lamellar fusion, aneurism, cytoplasmic vacuolation, nuclear alteration, necrotic muscle fiber and pyknotic nuclei in the gills, liver and muscles of C. carpio. ZnO NPs exposure significantly up-regulated the overlapping expressions of SOD1, CAT, GPx1a, GST-α, CYP1A, and Nrf-2 genes. A higher level of Zn bioaccumulation was observed in the following order: gill (35.03 ± 2.50 μg g^-1), liver (5.33 ± 0.73 μg g^-1) and muscle (2.30 ± 0.20 μg g^-1) at 1.146 mg L^-1 exposure of ZnO NPs. Hence, the current study indicated that the biogenic ZnO NPs generate toxicity in fishes by modifying the antioxidant defense mechanisms, histomorphology, and oxidative stress encoding genes.

Chironomus sancticaroli generation test applied to chemical contaminants and freshwater sediment samples

The use of ecotoxicological bioassays has been increasing due to the importance of understanding the effects of substances on biota and to help environmental agencies determine water and sediment qualities. The use of Chironomus sp. in laboratory bioassays is extensive, but there is still a lack of studies regarding the application of extended ecotoxicological tests, which evaluate different population generation responses and show a detailed impact on their development. The present study investigated the response of Chironomus sancticaroli, a Brazilian endemic insect, to 17α-ethinylestradiol hormone, caffeine anhydrous, LAS (linear alkylbenzene sulfonate), and environmental samples (sediments) in relation to wing length, fecundity, and larval length over three generations. Statistically, differences for all contaminants between P (parental), F1, and F2 generations (p ≤ 0.05) were observed, indicating that in the environment, the organism may be negatively affected when exposed to contaminants in successive generations. Different ecological responses were also noted in comparison to classic acute (96h) and chronic (10 days) ecotoxicological tests using Chironomus sancticaroli. Our results highlight that the generation test can present more detailed results regarding the effects of stressors on the organism's life cycle than do the classic bioassays.

Use of nontarget organism Chironomus sancticaroli to study the toxic effects of nanoatrazine

Atrazine was banned by the European Union in 2004, but is still used in many countries. Agricultural research employing nanotechnology has been developed in order to reduce the impacts to the environment and nontarget organisms. Nanoatrazine was developed as a carrier system and have been considered efficient in weed control. However, its toxicity must be verified with nontarget organisms. In this context, the aim of the present study was to investigate ecotoxicological effects of solid lipid nanoparticles (empty and loaded with atrazine) and atrazine on Chironomus sancticaroli larvae, evaluating the endpoints: mortality, mentum deformity, development rate and biochemical biomarkers. The contaminant concentrations used were 2, 470, 950, and 1900 μg L^-1 in acute (96 h) and 2 μg L^-1 in subchronic (10 days) bioassays. An environmentally relevant concentration of atrazine (2 μg L^-1) presented toxic and lethal effects towards the larvae. The nanoparticles loaded with atrazine showed toxic effects similar to free atrazine, causing mortality and biochemical alterations on the larvae. The nanoparticle without atrazine caused biochemical alterations and mortality, indicating a possible toxic effect of the formulation on the larvae. In the acute bioassay, most concentrations of nanoparticles loaded with atrazine were not dose dependent for the endpoint mortality. Only the atrazine concentration of 470 μg L^-1 was statistically significant to endpoint mentum deformity. The atrazine and nanoparticles (with and without atrazine) did not affect larval development. The results indicate that Chironomus sancticaroli was sensitive to monitor nanoatrazine, presenting potential to be used in studies of toxicity of nanopesticides.

Impact of 2,4-D and fipronil on the tropical midge Chironomus sancticaroli (Diptera: Chironomidae)

Increased use of pesticides in conventional agriculture implies potential risks to the environment. In aquatic ecosystems, benthic organisms may be exposed to pesticides via contaminated water and sediment, leading to several potential cascading effects on the food web. The aim of this study was to assess the functional implications of environmental realistic concentrations of the herbicide 2,4-D and the insecticide fipronil (alone and in combination) to the native tropical chironomid Chironomus sancticaroli. These two pesticides are widely applied to different crops and have frequently been detected (together) in surface water bodies in Brazil and elsewhere. Commercial products containing fipronil (Regent® 800WG) and 2,4-D (DMA® 806BR) were evaluated in 8-day toxicity tests for their effects on larval survival, growth (body length and biomass), head capsule width, development, and mentum deformities. Fipronil decreased the larval survival at the highest test concentration and the effective concentrations (EC) after eight days of exposure were: EC₁₀ = 0.48 µg L^-1 (0.395-0.565), EC₂₀ = 1.06 µg L^-1 (0.607-1.513), and EC₅₀ = 3.70 µg L^-1 (1.664-5.736). All sublethal test concentrations of fipronil decreased the larval growth, causing reductions in biomass up to 72%. The two highest test concentrations of fipronil decreased the head capsule width and after exposure to 3.7 µg fipronil L^-1, only half of the larvae reached the fourth instar. The incidence of deformities was increased by fipronil in a concentration dependent manner with an increase ranging from 23% to 75%. The highest test concentration of 2.4-D (426 µg L^-1) decreased the head capsule width, but larval development was unaffected at all concentrations evaluated. In the mixture tests, antagonism was observed at lower fipronil concentrations and synergism at higher fipronil concentrations for growth. The incidence of deformities rose with increasing fipronil concentrations. The results showed that environmental realistic concentrations of fipronil may have serious ecological implications for C. sancticaroli populations and that a mixture with the herbicide 2,4-D can have synergistic effects, potentiating the risks to the aquatic ecosystem.

Mediation of oxidative stress toxicity induced by pyrethroid pesticides in fish

Organophosphate and organochlorine pesticides are banned in most countries because they cause high toxicity and bioaccumulation in non-target organisms. Pyrethroid pesticides have been applied to agriculture and aquaculture since the 1970s to replace traditional pesticides. However, pyrethroids are approximately 1000 times more toxic to fish than to mammals and birds. Fish-specific organs such as the gills and their late metabolic action against this type of pesticide make fish highly susceptible to the toxicity of pyrethroid pesticides. Oxidative stress plays an important role in the neurological, reproductive, and developmental toxicity caused by pyrethroids. Deltamethrin, cypermethrin, and lambda-cyhalothrin are representative pyrethroid pesticides that induce oxidative stress in tissues such as the gills, liver, and muscles of fish and cause histopathological changes. Although they are observed in low concentrations in aquatic environments such as rivers, lakes, and surface water they induce DNA damage and apoptosis in fish. Pyrethroid pesticides cause ROS-mediated oxidative stress in fish species including carp, tilapia, and trout. They also cause lipid peroxidation and alter the state of DNA, proteins, and lipids in the cells of fish. Moreover, changes in antioxidant enzyme activity following pyrethroid pesticide exposure make fish more susceptible to oxidative stress caused by environmental pollutants. In this review, we examine the occurrence of pyrethroid pesticides in the aquatic environment and oxidative stress-induced toxicity in fish exposed to pyrethroids.

Impacts of dietary supplementation with p-coumaric acid and indole-3-acetic acid on survival and biochemical response of honey bees treated with tau-fluvalinate

Pollinator populations are in decline worldwide. Multiple factors have been cited as potential causes to these declines. In honey bees, a combination of stressors is known to cause colony losses. Adequate nutrition is a key factor for honey bee growth and colony development. Several studies show that the nutritional quality of the diet is directly proportional to the ability of the bee to face challenges or stressors. We explored the effect of p-coumaric (600 μM) and indole-3-acetic acid (2, 20 or 200 μM) supplementation on the survival and activity of key detoxification enzymes of honey bees exposed to tau-fluvalinate. The dietary supplementation with p-coumaric and indole-3-acetic acids (20 μM) enhanced the survival of bees exposed to tau-fluvalinate (approximately 20%). We also showed that dietary p-coumaric acid increased the levels of cytochrome P450 and glutathione reductase activity in bees treated with tau-fluvalinate, as well as in the untreated controls, while glutathione-S-transferase activity was lower in treated bees than in untreated. In bees fed with indole-3-acetic acid, cytochrome P450 showed increased levels, however, glutathione-S-transferase showed the lowest activity. Moreover, the results showed that supplementation with p-coumaric and indole-3-acetic acids did not alter acetyl cholinesterase activity, nor did treatment with tau-fluvalinate. Altogether, the enzymatic changes related to the detoxification mechanisms observed in bees that were fed with p-coumaric and indole-3-acetic acids could be responsible for the increased survival of bees treated with tau-fluvalinate compared to those that received a control diet. The results presented in this study, together with previous studies, provide evidence of the importance of dietary phytochemicals in the response of honey bees to pesticide exposure. Moreover, these results are the first report of the beneficial effect of the phytohormone indole-3-acetic acid on the survival of honey bees treated with tau-fluvalinate.

Chironomus sancticaroli (Diptera, Chironomidae) as a Sensitive Test Species: Can We Rely on Its Use After Repeated Generations, Under Laboratory Conditions?

In ecotoxicological assays, previously selected and standardized organism tests are exposed to an environmental sample. Some species of the Chironomus genus have been extensively used in ecotoxicological assays. Among these, Chironomus tentans is usually utilized in the USA and Chironomus sancticaroli in Brazil. We conducted ecotoxicological bioassays to compare a population of C. sancticaroli, kept for 6 years under laboratory conditions, with a sylvatic population of the same species, collected in the field. The aim was to test the hypothesis that populations of C. sancticaroli, maintained in the laboratory for long periods, could have a different response to stressors/substances. We analyzed the responses of C. sancticaroli for potassium chloride, zinc chloride, potassium dichromate, linear alkylbenzene sulphonate (LAS) and caffeine. The results showed no significant differences between the two populations in the analyses and seems to indicate the possible use of C. sancticaroli from populations kept in the laboratory for long periods.

Chironomus sancticaroli (Diptera, Chironomidae) as a Sensitive Tropical Test Species in Laboratory Bioassays Evaluating Metals (Copper and Cadmium) and Field Testing

Despite that chironomids are the most widely used benthic insect test species worldwide, little research has been conducted so far with tropical chironomid representatives. This study was designed to evaluate the indigenous midge Chironomus sancticaroli as a candidate test species for use in tropical toxicity assessments. To this end, laboratory water-only toxicity tests were conducted evaluating copper and cadmium. Obtained lethal concentration values were overall comparable or lower than those reported for other chironomids, including those most commonly used in temperate regions (C. riparius and C. dilutus). In addition, C. sancticaroli was deployed in situ in the Monjolinho River (São Paulo State, Brazil), and toxicity of sediment from this river was evaluated in the laboratory. Several field water and sediment quality parameters also were measured to enable correlating these with the effects observed in these toxicity tests. Field sediment toxicity to C. sancticaroli appeared to be related with sediment endosulfan concentrations, whereas effects noted in the in situ test were likely due to low pH values measured in river water. Chironomus sancticaroli appears to be a suitable candidate for inclusion as a test species in tropical toxicity evaluations in both the laboratory and the field.

Lethal and sublethal effects of metal-polluted sediments on Chironomus sancticaroli Strixino and Strixino, 1981

The Cantareira Complex is one of the most important water supplies of the metropolitan region of São Paulo, Brazil. Previously, it was demonstrated that the sediments in this complex were polluted with metals and that Paiva Castro Reservoir-the last reservoir in the sequence, which receives water from the five previous reservoirs-was the reservoir with the greatest concentration of pollutants. Based on field data, it was noticed that copper concentrations in sediments were related to morphological alterations in chironomids. The present study provides novel monitoring methods and results for the complex by isolating the environmental and biological sources of variation. An adaptation of the in situ assay proposed by Soares et al. (Arch Environ Contam Toxicol 49:163-172, 2005), which uses a native tropical Chironomus species and low-cost materials, is also provided. The aim of this study was to isolate the effects of sediments from Paiva Castro on controlled populations of C. sancticaroli larvae using an in situ assay. A seven-day experiment was performed in triplicate. Third instar larvae were inoculated in chambers containing sediments from two distinct regions of Paiva Castro reservoir and a control site with sand. Five biological responses were considered: mouthpart alterations, larval length, width of cephalic capsule, mortality and total damage. The results suggest the effects of sediment toxicity on larvae include a reduction in length and a higher occurrence of total damage.

Benzo(a)pyrene Exposure Causes Genotoxic and Biochemical Changes in the Midge Larvae of Chironomus sancticaroli Strixino & Strixino (Diptera: Chironomidae)

Benzo(a)pyrene (BaP) is a carcinogenic polycyclic aromatic hydrocarbon, also found in nature due to human activities. BaP adheres to sediments showing toxic effects on benthic organisms, including midge larvae of the family Chironomidae. We tested for toxic effects of benzo(a)pyrene on Chironomus sancticaroli Strixino & Strixino 1981 using biochemical and genotoxic biomarkers, to identify changes in metabolic and antioxidant pathways, besides neurotoxic and DNA damage. Enzyme activity was compared by exposing larvae to four nominal concentrations (0.47, 2.13, 3.41, and 4.73 μg l^-1) and DNA damage to two concentrations (0.47 and 4.73 μg l^-1), after exposure at 24, 48, 72, and 96 h. BaP caused neurotoxic effect, showing acetylcholinesterase alterations at different treatments. Changes in the biotransformation pathway were detected, with an increased activity of alpha and beta esterase in 48 h and reduction of glutathione-S-transferase activity in all periods at the highest concentrations. Damage to the antioxidant system was observed by the increase of the superoxide dismutase and reduction of the catalase, in 48 h. Genotoxicity was detected by an increased DNA damage at 48 and 72 h. The lowest concentration (0.47 μg l^-1), even presenting low mortality, also altered the biochemical parameters of the larvae. Thus, these results indicate that BaP causes metabolic, neurotoxic, and genotoxic effects on C. sancticaroli, even at low concentrations and short-term exposure. BaP can cause damage of immature invertebrates, and the ecological dynamics can be affected, since these organisms have trophic importance in the aquatic environment.

Polybrominated diphenyl ethers (PBDEs) effects on Chironomus sancticaroli larvae after short-term exposure

In-vivo effects of polybrominated diphenyl ethers (PBDEs) containing 3, 4 and 5 bromine atoms were tested on fourth-instar larvae of Chironomus sancticaroli (Diptera: Chironomidae) after 48h of exposure, by measuring the activity of the acetyl cholinesterase, alpha and beta esterases and glutathione S-transferase. The PBDE congeners 2,2',4-triBDE (BDE-17), 2,2',4,4'-tetraBDE (BDE-47) and 2,2',4,4',5-pentaBDE (BDE-99) were evaluated at 0.5, 1.0, 2.0 and 3.0ngmL^-1. Acetyl cholinesterase activity decreased significantly (p≤0.05) at all evaluated concentrations of the three PBDE congeners, except for larvae exposed to BDE-17 at 1.0 and 2.0ngmL^-1. The significant inhibition of acetyl cholinesterase activity ranged from 18% (BDE-47 at 0.5ngmL^-1) to 72% (BDE-47 at 2.0ngmL^-1). The enzymes alpha and beta esterase were also affected by the three congeners, reducing their activity from 14% (BDE-99 at 1.0ngmL^-1) to 52% (BDE-47 at 2.0ngmL^-1) and from 7% (BDE-99 at 2.0ngmL^-1) to 34% (BDE-47 at 3.0ngmL^-1) respectively. Substantial increments in glutathione S-transferase activity were similarly observed, varying from 138% (BDE-99 2.0 at ng mL^-1) to 346% (BDE-17 at 1.0ngmL^-1). DNA strand breaks were detected exclusively in larvae exposed to BDE-99 at 2.0 and 3.0ngmL^-1 (H=11.7, p=0.019). These results showed that C. sancticaroli larvae were sensitive to the PBDEs treatments under the experimental conditions.

Use of cholinesterase activity as an ecotoxicological marker to assess anatoxin-a(s) exposure: Responses of two cladoceran species belonging to contrasting geographical regions

The specificity of cholinesterase (ChE) activity to detect the presence of anatoxin-a(s) and sublethal effects of a 7-day exposure to Anabaena spiroides extract containing anatoxin-a(s) were assessed in two freshwater cladoceran species. Activities of ChE of both Pseudosida ramosa and Daphnia magna can be used to indicate the presence of the neurotoxin anatoxin-a(s), but not for the hepatotoxic microcystin. Activity of ChE of P. ramosa, however, performed better as a biomarker of exposure to A. spiroides than that of D. magna. Furthermore, sublethal exposure to A. spiroides extract significantly inhibited the ChE activity in P. ramosa and negatively affected both individual and population endpoints. For D. magna, the inhibition of ChE activity was not related to effects at higher levels of biological organization, since no direct effect was recorded on the individual and population endpoints. The activity of ChE in P. ramosa also proved to be a good predictor of chronic effects of the A. spiroides extract at higher levels of biological organization, since 48-h ChE inhibition was linked to the sublethal effects on the individual and population. These relationships could not be established for D. magna. Since relationships between the effects of A. spiroides extract at different levels of biological organization were species-specific, it can be concluded that the choice of test organism interferes with the accuracy of the environment risk assessment of this neurotoxin and, hence, the use of native species is recommended for its assessment.

Developing antibodies from cholinesterase derived from prokaryotic expression and testing their feasibility for detecting immunogen content in Daphnia magna

To yield cholinesterase (ChE) from prokaryotic expression, the ChE gene that belongs to Daphnia magna was amplified by reverse transcription-polymerase chain reaction (RT-PCR) using forward primer 5'-CCCYGGNGCSAT GATGTG-3' and reverse primer 5'-GYAAGTTRGCCCAATATCT-3'. To express the gene, one sequence of the amplified DNA, which was able to encode a putative protein containing two conserved carboxylesterase domains, was connected to the prokaryotic expression vector PET-29a(+). The recombinant vector was transformed into Escherichia coil BL21 (DE3). Protein expression was induced by isopropy-D-thiogalactoside. The expressed ChE was used as an immunogen to immunize BALB/c mice. The obtained antibodies were tested for their specificity towards crude enzymes from species such as Alona milleri, Macrobrachium nipponense, Bombyx mori, Chironomus kiiensis, Apis mellifera, Eisenia foetida, Brachydanio rerio, and Xenopus laevis. Results indicated that the antibodies had specificity suitable for detecting ChE in Daphnia magna. A type of indirect and non-competitive enzyme-linked immunosorbent assay (IN-ELISA) was used to test the immunoreactive content of ChE (ChE-IR) in Daphina magna. The detection limit of the IN-ELISA was found to be 14.5 ng/ml at an antiserum dilution of 1:22 000. Results from tests on Daphnia magna exposed to sublethal concentrations of triazophos indicated a maximal induction of 57.2% in terms of ChE-IR on the second day after the animals were exposed to a concentration of 2.10 μg/L triazophos. Testing on animals acclimatized to a temperature of 16 °C indicated that ChE-IR was induced by 16.9% compared with the ChE-IR content detected at 21 °C, and the rate of induction was 25.6% at 10 °C. The IN-ELISA was also used to test the stability of ChE-IR in collected samples. Repeated freezing and thawing had no influence on the outcome of the test. All these results suggest that the polyclonal antibodies developed against the recombinant ChE are as efficient as those developed against the native ChE in detecting ChE content in Daphnia magna.

A 3-year study on occurrence of emerging contaminants in an urban stream of São Paulo State of Southeast Brazil

This manuscript reports a 3-year study on occurrence of pharmaceuticals, hormones, and triclosan in surface waters of a central urban region of São Paulo State of Southeast Brazil (the Monjolinho River in São Carlos). Water samples collected once at every 2 months were pre-concentrated by solid-phase extraction (SPE) and analyzed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The most frequently detected compounds in higher concentrations were caffeine, paracetamol, and atenolol (maximum concentrations 129,585, 30,421, and 8199 ng L(-1), respectively), while hormones estrone and 17-β-estradiol were the least detected, in levels up to 14.8 ng L(-1). There was an increasing trend in concentrations of most of the compounds along the river course, especially downstream of the river where there is discharge of both wastewater treatment plant effluent and raw sewage from a particular region of São Carlos city. Concentrations of contaminants were higher during dry periods as a result of decline in the water levels. Decrease in concentrations near the river mouth occurred to different extents for each compound. It was high for caffeine and atenolol, but was very low for carbamazepine and diclofenac. The present study reports the first data about the occurrence of some major emerging contaminants in the Monjolinho River. Besides its regional significance, this work may assist in composing a dataset for water contamination diagnosis focusing on emerging contaminants, both in the Brazilian as well as in the Global studies related to aquatic ecosystems. Such datasets can be helpful for making future public policies on water quality, since these compounds are not yet legally regulated.

Acute effects of Anabaena spiroides extract and paraoxon-methyl on freshwater cladocerans from tropical and temperate regions: links between the ChE activity and survival and its implications for tropical ecotoxicological studies

Cholinesterase (ChE) activity was measured in Pseudosida ramosa and Daphnia magna, which had previously been exposed to Anabaena spiroides extract or to paraoxon-methyl for 48 h. These activities were then related to survival at 48 h. For A. spiroides extract, the observed 48-h LC50 was 2.27 and 2.70 × 10(6)cells mL(-1), while for paraoxon-methyl it was 0.60 and 2.17 μg L(-1), respectively, for P. ramosa and D. magna. Dose-response relationships were obtained for both P. ramosa and D. magna, when exposed to A. spiroides extract or paraoxon-methyl. Thus, when the tested concentrations of the toxicants increased, ChE activity and survival decreased. The ratio between 48-h IC50 for ChE and 48-h LC50 ranged from 75% to 81% for P. ramosa and from 77% to 81% for D. magna. This indicated that the concentrations of both A. spiroides extract and paraoxon-methyl that cause 50% mortality also inhibit ChE activity by 50%. Also, it was found that, for P. ramosa, a 50% inhibition of ChE activity was associated with a survival of 59.5% and 60.9%, respectively, for A. spiroides extract and paraoxon-methyl. However, for D. magna, at high levels of inhibition of ChE activity, almost no mortality was detected. In this specific case, 50% inhibition of the ChE activity was associated with 90.4 and 95.4% survival for A. spiroides extract and paraoxon-methyl, respectively. In contrast, enzyme inhibition slightly above 60% had a strong detrimental effect on survival in D. magna. These different patterns found in the relationship between ChE inhibition and survival may be due to species-specific differences in the affinities of both acetylcholinesterase and pseudocholinesterases, since the cladoceran ChE assays were performed with whole-body homogenates. In conclusion, when using ChE as a biochemical biomarker in risk assessment of cyanobacterial neurotoxic blooms in tropical regions, it is strongly recommended that native species are used, since our results revealed that P. ramosa was more sensitive than D. magna for both assay endpoints and both toxicants. Furthermore, the relationship between ChE activity and survival had a species-specific response. Therefore, the use of the model species D. magna in acute toxicity tests and ChE assays in tropical regions may lead to errors in the estimation of risks to the local species.

Purification and studies on characteristics of cholinesterases from Daphnia magna

Due to their significant value in both economy and ecology, Daphnia had long been employed to investigate in vivo response of cholinesterase (ChE) in anticholinesterase exposures, whereas the type constitution and property of the enzyme remained unclear. A type of ChE was purified from Daphnia magna using a three-step procedure, i.e., Triton X-100 extraction, ammonium sulfate precipitation, and diethylaminoethyl (DEAE)-Sepharose™-Fast-Flow chromatography. According to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), molecular mass of the purified ChE was estimated to be 84 kDa. Based on substrate studies, the purified enzyme preferred butyrylthiocholine iodide (BTCh) [with maximum velocity (Vmax)/Michaelis constant (Km)=8.428 L/(min·mg protein)] to acetylthiocholine iodide (ATCh) [with Vmax/Km=5.346 L/(min·mg protein)] as its substrate. Activity of the purified enzyme was suppressed by high concentrations of either ATCh or BTCh. Inhibitor studies showed that the purified enzyme was more sensitive towards inhibition by tetraisopropylpyrophosphoramide (iso-OMPA) than by 1,5-bis(4-allyldimethylammoniumphenyl) pentan-3-one dibromide (BW284C51). Result of the study suggested that the purified ChE was more like a type of pseudocholinesterase, and it also suggested that Daphnia magna contained multiple types of ChE in their bodies.

Biomarker responses as indication of contaminant effects in Oreochromis niloticus

The current study investigated oxidative stress parameters (enzymes activities, metallothionein content and lipid peroxidation) in freshwater fish, Oreochromis niloticus, tilapia exposure to Monjolinho River (in 4 months of year: January, April, July and November). One critical site in Monjolinho River (site B) was assessed in comparison to a reference site (site A). Water pH and oxygen concentration was lower than that recommended by CONAMA (Brazilian National Environmental Committee), resolution 357/2005 for protection of aquatic communities, and ammonium and the metals Cu, Zn, Mn and Fe (on all months) concentrations were higher than the maximum concentration recommended. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were significantly decreased in liver and muscle in tilapia from Monjolinho River, throughout the year, in relation to reference except in gills that SOD activity increased. Glutathione S-transferase (GST) activity was significantly increased in liver of the tilapia from Monjolinho River in all sites, in relation to reference except in gills that GST activity increased in July and decreased in November, suggesting that GST activity could be induced to neutralize the pollutants toxicity. On the other hand, GST activity was significantly decreased in white muscle indicating a toxic effect of pollutants, resulting in a decreased ability of tilapia to perform defense reactions associated to GSTs. The decrease of catalase (CAT) activity in gills of the O. niloticus together with the increase of SOD activity, could explain the increased lipid peroxidation (LPO) level in this organ. Metallothionein levels in liver and gills were significantly high in all sites. Results indicate that the exposure to metals caused severe damage to tissues; despite the consensually assumed antioxidant induction as a sign of exposure to contaminants the effects seem in part to be mediated by suppression of antioxidant system with SOD, CAT and GPx as potential candidates for tissues toxicity biomarkers of pollutants.