Experimental study on effects of prometryn exposure scenarios on Microcystis aeruginosa growth and N and P concentrations.

Single exposure toxicity tests of herbicides like prometryn are commonly applied in studying ecological and environmental issues, but they are more likely exposed to microalgae through multiple applications of irrigation and water flow. The toxicity of prometryn towards Microcystis aeruginosa (M. aeruginosa) at different growth stages (different exposure period) was determined by single and multiple exposures (different exposure mode) through 39-day batch-experiment comparison study. Inhibition rates showed that M. aeruginosa growth was greatly inhibited by exposure to prometryn in a final concentration of 80 and 160 µg·L-1 (p < 0.05). Specifically, with the same prometryn exposure periods (lag or exponential phase) and concentrations, a single exposure displayed larger toxicity on M. aeruginosa than repetitive additions of prometryn in general according to inhibition rates. Moreover, with the same prometryn exposure modes and concentrations, inhibitory effect was higher with prometryn exposure in lag phase than that in exponential phase according to M. aeruginosa densities and inhibition rates. In general, variations of total dissolved phosphorus (TDP) and total dissolved nitrogen (TDN) with time responded negatively to M. aeruginosa growth, and added prometryn inhibits the utilization rate of both P and N. Logistic function was well used to describe algae densities (R2 = 0.979 ~ 0.995), growth rates (R2 = 0.515 ~ 0.731), specific growth rates (R2 = 0.301 ~ 0.648) and inhibition rates (R2 = 0.357 ~ 0.946) along with its combination with Monod function. In addition, results showed that shifts of limiting nutrients could be prompted by not only M. aeruginosa growth but also prometryn exposure scenarios. This study provides a basis for studying the potential harm of prometryn to the ecological environment.

Effects of chronic prometryn exposure on antioxidative status, intestinal morphology, and microbiota in sea cucumber (Apostichopus japonicus).

Prometryn is an occasional triazine herbicide used in aquaculture to kill algae. However, deposition of prometryn at the bottom of the pond poses a potential threat to aquatic animals, especially benthos, such as the sea cucumber. This study investigated the toxic effects of prometryn oral exposure on antioxidants, and the intestinal histomorphology and microbiome of sea cucumbers. Results showed that the accumulation of prometryn in the intestine, respiratory tree, and body wall decreased sequentially under the same level. Severe pathological damages were observed in the intestines of sea cucumbers fed with 0.080 and 1.595 g/kg prometryn (measured concentration). Moreover, hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations were significantly increased in prometryn treatment groups compared to the control group (P < 0.05), while the catalase (CAT) activity was significantly decreased (P < 0.05) in the coelomic fluid of treatment groups. At the phylum level, the abundance of Proteobacteria was significantly higher in the 0.080 g/kg treatment group than in the control group. In addition, prometryn exposure reduced the diversity of intestinal microflora in sea cucumbers. In conclusion, these results suggest that prometryn has potential toxicity to sea cucumber. Therefore, the harm of prometryn deposited in the sediment to aquatic animals must be a concern in aquaculture.

Effects of fish feed addition scenarios with prometryn on Microcystis aeruginosa growth and water qualities.

The number of undesirable environmental impacts of fish feed has been reported widely. Although repeated fish feed exposures are more prospective to occur in water, previous studies were mostly conducted as a single exposure of fish feed. In order to fill these gaps, a 40 days incubator experiment was conducted to explore the effects of fish feed addition scenarios during the lag phase with prometryn on both Microcystis aeruginosa growth and concentrations of nutrients. The maximum algae densities in groups of single exposure were 6.0-26.2% and 8.8-74.4% higher than those in groups of double and triple exposures, respectively (P < 0.05). At the beginning of the experiment, concentrations of nutrients in groups with different feed exposure scenarios were significantly different. The pattern of nutrient limitation showed a transformation from phosphorus limitation to nitrogen limitation generally. Furthermore, the average inhibition rates of algae by prometryn in the case of a single fish feed exposure were 4.6-9.4% lower than those under double exposures, and 22.0-26.8% lower than those under triple exposures (P < 0.05). In addition, algae growth rates have been developed as a function of concentrations of consumed nutrients (R2 = 0.410-0.932). Based on the above results, we concluded that in terms of limiting algae growth multiple low-dosage additions of fish feed were considered as a better addition pattern. By optimizing feed addition scenarios, there is considerable potential to increase the environmental sustainability of aquaculture.

Transcriptome analysis of Penaeus vannamei hepatopancreas reveals differences in toxicity mechanisms between phoxim and prometryne.

Due to overuse and terrestrial input, there are large quantities of phoxim and prometryne residues in some aquatic environments. In the present study, the effects of these compounds on Penaeus vannamei hepatopancreas were analysed at the transcriptome level to investigate toxicity in this nontarget aquaculture organism. Twelve normalised cDNA libraries were constructed using RNA from phoxim and prometryne treatment groups, and an untreated control group. A total of 667,750,902 clean reads were obtained. Analysis of differentially expressed genes (DEGs) identified 449 in control vs phoxim groups, 185 in control vs prometryne groups, and 183 in prometryne vs phoxim groups. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, arachidonic acid metabolism, pancreatic secretion, linoleic acid metabolism, and beta-alanine metabolism pathways were significantly enriched in control vs phoxim groups. In control vs prometryne groups, lysosome, pentose and glucuronate interconversion, antigen processing and presentation, and glycosaminoglycan degradation pathways were significantly enriched. In prometryne vs phoxim groups, protein digestion and absorption, extracellular matrix (ECM)-receptor interaction, PI3K-Akt signalling, cell adhesion molecule (CAM), AGE-RAGE signalling related to diabetic complications, focal adhesion, and renin secretion pathways were significantly enriched. In further detailed analysis, glutathione S-transferase (GST), glutathione peroxidase and basic phospholipase A2 were downregulated in the phoxim treatment group, indicating that phoxim damaged hepatopancreas. Upregulation of phospholipase A2 (secretory phospholipase A2-like) indicates possible inflammatory pathological injury to hepatopancreas caused by phoxim. Meanwhile, downregulation of CD63 indicates that prometryne affect the immune system.

Evaluation of the Rhizosphere Contribution to the Environmental Fate of the Herbicide Prometryn.

Plant protection products (PPPs) undergo rigorous regulatory assessment to ensure that they do not pose unacceptable risks to the environment. Elucidation of their fate and behavior in soil is an integral part of this environmental risk assessment. The active substance degradation in soil of PPPs is first assessed in laboratory studies (typically following Organisation for Economic Co-operation and Development [OECD] test guideline 307). Conditions in guideline laboratory studies are far removed from those occurring under agricultural use, and the contribution of crop roots has currently not been assessed. We integrated viable plant root systems, representative of 3 different crop types, into the OECD test guideline 307 design to assess their impact on the dissipation of the herbicide prometryn. Significantly faster decline of parent residue and higher formation of nonextractable residues were observed in all 3 planted systems. This led to a reduction in the time required for 50% of the compound to dissipate (DT50) of approximately one-half in the presence of rye grass and hot pepper and of approximately one-third in the presence of red clover. These findings imply that plants and their associated root networks can have a significant influence on PPP dissipation. Based on these data, greater environmental realism could be added to the standardized laboratory study design by the inclusion of plant root systems into higher tier studies, which, in turn, could serve to improve the environmental risk assessment process. Environ Toxicol Chem 2020;39:450-457. © 2019 SETAC.

Combination of Logistic and modified Monod functions to study Microcystis aeruginosa growth stimulated by fish feed.

The ecological health of aquaculture water is threatened by wasted fish feed and herbicides. In order to study the effect of prometryn and fish feed on Microcystis aeruginosa growth based on Monod and Logistic functions, four different concentrations of prometryn (0, 50, 100 and 200 µg L-1) and two different dosages of fish feed (0.075 g, 0.15 g; d < 0.85 mm) were added into the culture medium, and the fish feed was the source of nitrogen and phosphorus in the MII medium. Results showed that Microcystis aeruginosa growth can be fitted well by Logistic and modified Logistic functions with 0-200 µg L-1 prometryn (R2 = 0.981-0.998 and R2 = 0.989-0.999, respectively). With the same concentration of prometryn, the maximum algae density (Nmax) of Microcystis aeruginosa calculated by both Logistic and modified Logistic functions increased with increasing dosage of fish feed and with the same dosage of fish feed, Nmax declined with increasing concentrations of prometryn. Inhibition of prometryn on algae growth stimulated by fish feed is of double concentration-dependence, inhibition rates (I) are lower in 0.15 g fish feed medium than 0.75 g ones generally, implying that more nutrients can alleviate the stress caused by prometryn on algae. Derived formula for the specific growth rate, growth rate and inhibition rate using modified Logistic function agreed reasonably well with measured data. Jointly application of modified Monod and Logistic functions can better describe the relationship between specific growth rates and nutrients concentrations compared to combination of Monod and Logistic functions. In addition, equations for describing variations of nutrients concentrations (PO43--P and NH4+-N) with time were also derived based on both modified Monod and Logistic functions, which agree reasonably well with the measured data. In sum, the combination of modified Monod and Logistic functions provides a promising and robust method in studying algal growth stimulated by fish feed in incubator experiments.

Prometryn and humic acid induce Cytochrome P450 1A expression in Danio rerio (zebrafish).

Humic acid (HA) is a major component of dissolved organic matter, is ubiquitous in the aquatic environment and influences the biological toxicity of organic pollutants. In this study, we investigated the cytochrome P450 1A (CYP 1A) mRNA expression and ethoxyresorufin-O-deethylase (EROD) activity in the gills and liver of zebrafish following exposure to the s-triazine herbicide prometryn with or without HA present. Prometryn induced both CYP 1A mRNA expression and EROD activity. The CYP 1A mRNA expression of zebrafish that were exposed to a combination of prometryn and HA was increased compared to those exposed to prometryn alone. A likely cause for CYP 1A induction is the impact of special components of HA, functioning as aryl hydrocarbon receptor (AHR) agonists. In combination with HA, these increase prometryn levels in tissues. Similar results for EROD activity were evident. In our time course study, CYP 1A mRNA expression reached maximum values during 24h. This revealed CYP 1A mRNA transcription as a comparatively sensitive toxicity index. In a recovery experiment, we found a faster decrease of CYP 1A mRNA expression to control levels (CK) in gills compared to liver tissue. Following exposure to HA, CYP 1A mRNA expression in liver tissue displayed a faster decrease to CK levels. HA induced enhanced metabolic rates for prometryn. In contrast, recovery regularity of CYP 1A expression in gills was independent of the presence of HA. This result indicates different detoxification mechanisms for HA in liver and gills.

Toxicity of environmental Gesagard to goldfish may be connected with induction of low intensity oxidative stress in concentration- and tissue-related manners.

Prometryn is a selective herbicide commonly used in agriculture as the commercial preparation, Gesagard. Goldfish (Carassius auratus) exposure for 96h to 0.2, 1, or 5mgL(-1) Gesagard 500FW (corresponding to 0.1, 0.5, and 2.5mgL(-1) of prometryn) on indices of oxidative stress (lipid peroxides, protein carbonyls, and thiol content) and activities of antioxidant and related enzymes in gills, liver, and kidney was studied. Gills appeared to be the most resistant to Gesagard treatment, reacting to only the highest concentration of herbicide with enhanced levels of low molecular mass thiols and activities of glutathione S-transferase (GST) and glutathione reductase. Goldfish exposure to 0.2-5mgL(-1) Gesagard resulted in enhancement of carbonyl protein level and activity of superoxide dismutase (SOD), but reduced the lipid peroxide (LOOH) content and activity of glutathione peroxidase in liver. Kidney appeared to be the main target organ of Gesagard toxicity, showing the greatest number of parameters affected even under low concentrations of herbicide. An increase in the content of L-SH and activity of SOD was accompanied with decreased activities of catalase, GST, and glucose-6-phosphate dehydrogenase and reduced levels of LOOH in kidney of Gesagard treated fish. The treatment also induced various histological changes in goldfish liver and kidney which could be related to their dysfunction. The present study indicates that Gesagard induced oxidative stress of differing intensities in the three goldfish tissues and demonstrated that kidney would be the best target organ to analyze, reveal, and monitor Gesagard effects on fish.

Effects of prometryne on early life stages of common carp (Cyprinus carpio L.).

Toxicity of prometryne to early life stages of common carp was assessed. On the basis of accumulated mortality in the experimental groups lowest observed-effect concentration (LOEC) was estimated as 1100 µg/l; and no observed-effect concentration (NOEC) was 850 µg/l. Fulton's condition factor was significantly lower than in controls in fish exposed to 4000 µg/l after 7, 14, and 21 days. By day 14, fish exposed to 4000 µg/l prometryne showed significantly lower mass and total length compared to controls. Fish exposed the 1200 and 4000 µg/l showed delay in development, severe hyperaemia in gill, liver, and caudal and cranial kidney. Subchronic prometryne exposure of early-life stages of common carp at concentrations of 1200 and 4000 µg/l affected their survival, growth rate, early ontogeny, and histology.

Probabilistic risk assessment of diuron and prometryn in the Gwydir River catchment, Australia, with the input of a novel bioassay based on algal growth.

A probabilistic risk assessment of the selected herbicides (diuron and prometryn) in the Gwydir River catchment was conducted, with the input of the EC50 values derived from both literature and a novel bioassay. Laboratory test based on growth of algae exposed to herbicides assayed with a microplate reader was used to examine the toxicity of diuron and prometryn on the growth of Chlorella vulgaris. Both herbicides showed concentration dependent toxicity in inhibiting the growth of Chlorella during the exposure period of 18-72 h. Diuron caused more toxicity as judged by growth rates than prometryn. Thalaba Creek at Merrywinebone was identified as the 'hotspot' for diuron and prometryn risk in the Gwydir catchment. The use of microplate assays coupled with probabilistic risk assessment is recommended for rapid assessment of ecotoxicity of indigenous species, allowing identification of locations in river catchments requiring environmental management.

Effect of prometryne on early life stages of marbled crayfish (Procambarus fallax f. virginalis).

OBJECTIVES: The aim of this study is to assess the toxicity of prometryne in early life stages of marbled crayfish (Procambarus fallax f. virginalis) on the basis of mortality, early ontogeny, growth rate, and histopathology during and at the end of the test. DESIGN: The early life stages of marbled crayfish were exposed to prometryne at four concentrations, 0.51, (reported concentration in Czech rivers), 144, 1440, and 4320 µg x l(-1) for 53 days and compared to crayfish in a non-treated control group. RESU LTS: Prometryne in concentration 144, 1444 and 4320 µg x l(-1) caused decrease of weight and specific growth rates of crayfish. Crayfish exposed the highest concentration 4320 µg x l(-1) showed delay in ontogeny development. All crayfish groups exposed to prometryne showed histopathological changes in gill. On the basis of histopathological changes the values of LOEC = 0.51 µg x l(-1) and NOEC = for 0.10 µg x l(-1) of prometryne for marbled crayfish juveniles was estimated. CONCLUSIONS: Chronic exposure of prometryne on early life stages of crayfish has affected their mortality, growth rate, and histology. Some of the changes were observed only at higher exposures (144, 1444 and 4320 µg x l(-1)), but histopathological changes in gills were observed also in crayfish exposed to the real environmental concentration in Czech rivers (i.e. 0.51 µg x l(-1)), which is about 9 times lower than maximal concentration (4.40 µg x l(-1)) reported in surface waters of Greece. Concentrations of prometryne in World rivers have been reported to generally vary in the range of 0.1-4.40 µg x l(-1).

Bioaccumulation and catabolism of prometryne in green algae.

Investigation on organic xenobiotics bioaccumulation/biodegradation in green algae is of great importance from environmental point of view because widespread distribution of these compounds in agricultural areas has become one of the major problems in aquatic ecosystem. Also, new technology needs to be developed for environmental detection and re-usage of the compounds as bioresources. Prometryne as a herbicide is widely used for killing annual grasses in China and other developing countries. However, overuse of the pesticide results in high risks to contamination to aquatic environments. In this study, we focused on analysis of bioaccumulation and degradation of prometryne in Chlamydomonas reinhardtii, a green alga, along with its adaptive response to prometryne toxicity. C. reinhardtii treated with prometryne at 2.5-12.5 µg L(-1) for 4 d or 7.5 µg L(-1) for 1-6 d accumulated a large quantity of prometryne, with more than 2 mg kg(-1) fresh weight in cells exposed to 10 µg L(-1) prometryne. Moreover, it showed a great ability to degrade simultaneously the cell-accumulated prometryne. Such uptake and catabolism of prometryne led to the rapid removal of prometryne from media. Physiological and molecular analysis revealed that toxicology was associated with accumulation of prometryne in the cells. The biological processes of degradation can be interpreted as an internal tolerance mechanism. These results suggest that the green alga is useful in bioremediation of prometryne-contaminated aquatic ecosystems.

Effect of chronic exposure to prometryne on oxidative stress and antioxidant response in early life stages of common carp (Cyprinus carpio L.).

OBJECTIVES: The aim of the study was to investigate effects of the triazine herbicide prometryne on early life stages of common carp Cyprinus carpio as indicated by oxidative stress and antioxidant indices. DESIGN: Toxicity tests were performed according to OECD 210 methodologies. Common carp larvae and embryos exposed for 35 days to prometryne at three concentrations, 0.51 (reported concentration in Czech rivers), 80 (1% 96 h LC50), and 1200 (15% 96 h LC50) µg/l, were compared to carp in a non-treated control group. Activity of superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), as well as levels of thiobarbituric acid reactive substances (TBARS) were assessed. RESULTS: Chronic exposure of early life stages of carp to prometryne showed no effect on growth and mortality rates. Levels of oxidative damage in fish test groups showed no significant differences from the controls. Glutathione reductase activity at exposure 0.51 µg/l was significantly increase (p<0.01) compared with controls and other exposures. CONCLUSION: The chronic exposure to prometryne showed no influence on oxidative stress. Differences from control fish was observed in GR activity in exposure prometryne 0.51 µg/l.

Active bio-monitoring of contamination in aquatic systems--an in situ translocation experiment applying the PICT concept.

The environmental risk assessment of toxicants is often derived from chemical monitoring, based on single species tests performed in the laboratory. However, to provide ecologically relevant information, community approaches are required. The aim of this study was to causally link prometryn exposure to community-level effects in complex field situations and to identify response times of adaptation to pollution and recovery from pollution. For this reason sensitivity shifts in communities were detected and related to structural changes within the periphyton community. Furthermore, it was intended to illustrate the possibility of a combined approach of community translocation and sensitivity assessment for active monitoring of polluted sites. Periphyton was grown at a reference (R) and at a polluted (P) site of the river Elbe basin for 26 days, was subsequently transferred from the polluted site to the reference site and vice versa. Sensitivity of communities to prometryn was determined according to the pollution-induced community tolerance (PICT)-concept in short-term tests by measuring photosynthesis inhibition and was related to structural changes in algal class and diatom species composition. Exposure to prometryn was determined using polar organic integrative samplers (POCIS), giving time-weighted average concentrations. Environmental concentrations of prometryn were significantly higher at the polluted site compared to the reference site. Communities grown at the polluted site showed a higher tolerance to prometryn in comparison to the reference site. 17 Days after the translocation to the reference site, EC(50) decreased 2-fold compared to the non-translocated P-community of the same age. By contrast, EC(50) of the community grown at the reference site was 5 times higher after 17 days exposure at the polluted site. Furthermore, P-R communities were less sensitive to prometryn (higher EC(50)) than R-P communities, 24 days after translocation. These changes in sensitivity to prometryn were consistent with changes in species composition and clearly indicate that the exposure history of communities is defining the time-response of recovery and adaptation. In conclusion, the PICT-concept is shown to be a suitable tool for analysis of recovery and adaptation processes of communities under natural conditions. Therefore, it improves the link between cause and effect in field situations. In situ translocation studies provide an ecological relevant assessment of pesticide effects under field conditions and could be used as a diagnostic tool in active monitoring for decision-making frameworks as used in the implementation of the European Water Framework Directive (WFD).

Brain toxicokinetics of prometryne in mice.

Prometryne is a methylthio-s-triazine herbicide. Significant trace amounts are found in the environment, mainly in water, soil, and food plants. The aim of this study was to establish brain and blood prometryne levels after single oral dose (1 g kg-1) in adult male and female mice. Prometryne was measured using the GC/MS assay at 1, 2, 4, 8, and 24 h after prometryne administration. Peak brain and blood prometryne values were observed 1 h after administration and they decreased in a time-dependent manner. Male mice had consistently higher brain and blood prometryne levels than female mice. The observed prometryne kinetics was similar to that reported for the structurally related herbicide atrazine.

Modelling long-term ecotoxicological effects on an algal population under dynamic nutrient stress.

We study the effects of toxicants on the functioning of phototrophic unicellular organism (an algae) in a simple aquatic microcosm by applying a parameter-sparse model. The model allows us to study the interaction between ecological and toxicological effects. Nutrient stress and toxicant stress, together or alone, can cause extinction of the algal population. The modelled algae consume dissolved inorganic nitrogen (DIN) under surplus light and use it for growth and maintenance. Dead algal biomass is mineralized by bacterial activity, leading to nutrient recycling. The ecological model is coupled with a toxicity-module that describes the dependency of the algal growth and death rate on the toxicant concentration. Model parameter fitting is performed on experimental data from Liebig, M., Schmidt, G., Bontje, D., Kooi, B.W., Streck, G., Traunspurger, W., Knacker, T. [2008. Direct and indirect effects of pollutants on algae and algivorous ciliates in an aquatic indoor microcosm. Aquatic Toxicology 88, 102-110]. These experiments were especially designed to include nutrient limitation, nutrient recycling and long-term exposure to toxicants. The flagellate species Cryptomonas sp. was exposed to the herbicide prometryn and insecticide methyl parathion in semi-closed Erlenmeyers. Given the total limiting amount of nitrogen in the system, the estimated toxicant concentration at which a long-term steady population of algae goes extinct will be derived. We intend to use the results of this study to investigate the effects of ecological (environmental) and toxicological stresses on more realistic ecosystem structure and functioning.

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.

The effects of prometryne on subchronically treated mice evaluated by SCGE assay.

Prometryne is a methylthio-s-triazine herbicide used to control annual broadleaf and grass weeds in many cultivated plants. Significant traces are documented in environment, mainly water, soil and plants used for human and domestic animal nutrition. Data on the toxic effects of prometryne and other methylthio-s-triazine have scorcely been published. The goal of this study was to investigate if prometryne, applied orally, could induce DNA damage in mouse leukocytes, in subchronical in vivo experimental design. Three different doses of prometryne were applied per os repeatedly every 48 hours. After the 7th dose (day 14) and the 14th dose (day 28) blood leucocytes were analyzed by alkaline Single Cell Gel Electrophoresis (Comet) assay. The results of three different comet parameters showed general increase in Olive tail moment, tail length and tail intensity values in treated groups of animals. The increase in measured values was almost proportional to the dose received and the time of exposure. We conclude that prometryne or its metabolic residues have the potential to induce processes that cause genotoxic effects on leukocytes on mice in in vivo repeated exposure.

Acute toxic effects of three pesticides on Pseudomonas putida monitored by microcalorimeter.

A series of calorimetric experiments were performed to investigate the toxic effects of beta-cypermethrin (BCP), bensulfuron-methyl (BSM) and prometryne (PM) on Pseudomonas putida (P. putida). The metabolic action of P. putida on the three pesticides was studied by obtaining power-time curves. The growth of P. putida was inhibited completely in each case when the concentrations of pesticides were up to 80 micro g mL(- 1). The relationships between the inhibitory ratio (k) and doses of contaminants were approximately linear for the three pesticides. The total heat dissipated per milliliter (Q(total)) for the pesticides decreased during the course of the experiment. The OD(600) of P. putida growth in the absence and presence of pesticides was also obtained. The power-time curves of P. putida growth coincided with its turbidity curves. This elucidates that microcalorimetric method agrees well with the routine microbiological method. Among these three pesticides, BSM was found to be the most toxic with an IC(50) of 19.24 micro g mL(- 1) against P. putida. PM exhibited moderate virulence with an IC(50) of 27.86 micro g mL(- 1) and BCP had the lowest toxicity with an IC(50) of 39.64 micro g mL(- 1).

Direct and indirect effects of pollutants on algae and algivorous ciliates in an aquatic indoor microcosm.

An aquatic indoor microcosm was used to study effects of the pesticides parathion-methyl and prometryn on phototrophic flagellates (Cryptomonas sp.) and predatory ciliates (Urotricha furcata). Parathion-methyl caused effects to flagellates and ciliates at the range of low mg L(-1), regardless of whether the organisms were exposed separately or combined in the multi-species test system. Prometryn caused effects on the flagellates at low microg L(-1) concentrations, resulting in a NOEC of 6.9 microg L(-1) in the single-species test and a NOEC of 15.2 microg L(-1) in the multi-species microcosm. For ciliates the NOEC decreased by factor 145 in the multi-species test compared to the NOEC of 2.2 mg L(-1) in the single-species test when exposed to prometryn. The lower NOEC for ciliates exposed to prometryn in the microcosm was most likely caused by an indirect effect due to reduced availability of flagellates as food. The measurement of nutrient concentrations in the test media and organisms facilitated the modelling of effects. The presented aquatic indoor microcosm is considered as a tool which could be standardised and applied as an instrument to provide data for higher tier risk assessment.