Comparative toxic and genotoxic effects of chloroacetanilides,formamidines and their degradation products on Vibrio fischeri and Chironomus riparius

Toxic and genotoxic effects of alachlor, metolachlor, amitraz, chlordimeform, their respective environmentally stable degradation products 2,6-diethylaniline, 2-ethyl-4-methylaniline, 2,4-dimethylaniline, and two other related compounds, 3,4-dichloroaniline and aniline were compared. Acute toxicity tests with Chironomus riparius (96 h) and Vibrio fischeri (Microtox) and genotoxicity tests with a dark mutant of V. fischeri (Mutato) were carried out. Our results demonstrate that toxicity and genotoxicity of the pesticides are retained upon degradation to their alkyl-aniline metabolites. In the case of the herbicides alachlor and metolachlor, the toxicity to V. fischeri was enhanced upon degradation. Narcosis alone explains toxicity of the compounds to the midge, but not so for the bacteria suggesting a disparity in the selectivity of the test systems. All compounds showed direct genotoxicity in the Vibrio test. but amitraz and its metabolite were genotoxic at concentrations 10(3)-10(5) lower than all the other compounds. The observations indicate that stable aniline degradation products of the pesticides may contribute considerably to environmental risks of pesticides application and that genotoxic effects may arise upon degradation of pesticides.     

(汍)汊湖水体和表层沉积物中有机氯农药分布特征

用GC/ECD内标法定量测定了(汍)汉湖水体和表层沉积物中的有机氯农药(OCPs).(汍)汊湖水样和表层沉积物中20种OCPs均有检出.表层沉积物上层中(0～2 cm)的OCPs明显高于下层(2～10 cm),这是(汍)汉湖具有稳定的水动力条件所致.氯丹在表层沉积物中浓度最高,与该化合物在环境中的强稳定性以及在该地区的大量使用有关.表层沉积物样品DCHsO2上层OCPs中o,p'-DDT主要成分,表明近期可能有新的DDTs,特别是含大量o,p'-DDT的三氯杀螨醇的使用.DDD/DDE则显示表层沉积物上层DDTs的降解主要处在厌氧条件下,而下层处在好氧条件下.     

Occurrence of PAHs, PCBs and organochlorine pesticides in the Tonghui River of Beijing, China

Tonghui River, a typical river in Beijing, People's Republic of China, was studied for its water and sediment quality, by determining the levels of 16 polycyclic aromatic hydrocarbons (PAHs), 12 polychlorinated biphenyls (PCBs) and 18 organochlorine pesticides in water and sediment samples. Total PAHs, PCBs and organochlorine pesticides concentrations in water varied from 192.5 to 2651 ng/l, 31.58-344.9 ng/l and 134.9-3788 ng/l, respectively. The total PAHs, PCBs and organochlorine pesticides concentrations in surficial sediments were 127-928 ng/g, 0.78-8.47 ng/g and 1.79-13.98 ng/g dry weight, respectively. The results showed that the concentration of these selected organic pollutants in sediment was higher than those in surface water. It may be due to the fact that organic hydrophobic pollutants tend to stay in the sediments. The PAHs were dominated by 2-, 3-ring components in water samples and by 3- and 4-ring compounds in sediment. For organochlorines, alpha-HCH, delta-HCH, Heptachlor, Endosulfan II, DDT are the major organochlorine pesticides in water while Heptachlor, Dieldrin and DDE composed of 95% of total organochlorine pesticides in sediment. For HCHs (HCHs=alpha-HCH+beta-HCH+gamma-HCH+delta-HCH), the predominance of alpha-HCH of total HCHs were clearly observed in water and sediment. PCB18, PCB31 and PCB52 were predominant in water, on average these compounds collectively accounted for 67% of total PCBs. But in sediment, the predominant compounds were PCB28, PCB31 and PCB153, which accounted for 71% of total PCBs in sediment. The levels of micro pollutants in our study areas were compared with other studies.     

Photolytic degradation of methyl-parathion and fenitrothion in ice and water: Implications for cold environments

Here we investigate the photodegradation of structurally similar organophosphorus pesticides; methyl-parathion and fenitrothion in water (20 °C) and ice (−15 °C) under environmentally-relevant conditions with the aim of comparing these laboratory findings to limited field observations. Both compounds were found to be photolyzed more efficiently in ice than in aqueous solutions, with quantum yields of degradation being higher in ice than in water (fenitrothion > methyl-parathion). This rather surprising observation was attributed to the concentration effect caused by freezing the aqueous solutions. The major phototransformation products included the corresponding oxons (methyl-paraoxon and fenitroxon) and the nitrophenols (3-methyl-nitrophenol and nitrophenol) in both irradiated water and ice samples. The presence of oxons in ice following irradiation, demonstrates an additional formation mechanism of these toxicologically relevant compounds in cold environments, although further photodegradation of oxons in ice indicates that photochemistry of OPs might be an environmentally important sink in cold environments.     

Determination photostability of selected agrochemicals in water and soil.

The photolysis of selected pesticides in aqueous solutions has been investigated. The photolysis produced different intermediate substances, which were also found to be soil and microbial degradation products. The phototransformation in the presence of TiO2 and humic substances leads to a disappearance of these compounds. The reaction rate is dependent on the semiconductor oxide and concentration. Photoproducts were isolated and characterized by different spectroscopic methods. Results from this study indicate that degradation products of isoproturon are more toxic on Daphnia magna than on the parent compound.     

Linking ground-water age and chemistry data along flow paths: implications for trends and transformations of nitrate and pesticides

Tracer-based ground-water ages, along with the concentrations of pesticides, nitrogen species, and other redox-active constituents, were used to evaluate the trends and transformations of agricultural chemicals along flow paths in diverse hydrogeologic settings. A range of conditions affecting the transformation of nitrate and pesticides (e.g., thickness of unsaturated zone, redox conditions) was examined at study sites in Georgia, North Carolina, Wisconsin, and California. Deethylatrazine (DEA), a transformation product of atrazine, was typically present at concentrations higher than those of atrazine at study sites with thick unsaturated zones but not at sites with thin unsaturated zones. Furthermore, the fraction of atrazine plus DEA that was present as DEA did not increase as a function of ground-water age. These findings suggest that atrazine degradation occurs primarily in the unsaturated zone with little or no degradation in the saturated zone. Similar observations were also made for metolachlor and alachlor. The fraction of the initial nitrate concentration found as excess N2 (N2 derived from denitrification) increased with ground-water age only at the North Carolina site, where oxic conditions were generally limited to the top 5 m of saturated thickness. Historical trends in fluxes to ground water were evaluated by relating the times of recharge of ground-water samples, estimated using chlorofluorocarbon concentrations, with concentrations of the parent compound at the time of recharge, estimated by summing the molar concentrations of the parent compound and its transformation products in the age-dated sample. Using this approach, nitrate concentrations were estimated to have increased markedly from 1960 to the present at all study sites. Trends in concentrations of atrazine, metolachlor, alachlor, and their degradates were related to the timing of introduction and use of these compounds. Degradates, and to a lesser extent parent compounds, were detected in ground water dating back to the time these compounds were introduced.     

Investigations of the determination and transformations of diazinon and malathion under environmental conditions using gas chromatography coupled with a flame ionisation detector

Degradation of two model insecticides, diazinon and malathion, and their degradation products 2-isopropyl-6-methyl-4-pyrimidinol--IMP (diazinon hydrolysis product) and malaoxon (malathion oxidation product) was compared and studied in the environment. The pesticides and their metabolites were extracted from samples (water, soil, chicory) with ethyl acetate and subsequently the extracts were analyzed by GC/FID. It was shown that hydrolysis is the major process in the degradation of these pesticides in water. In fact, 95% of diazinon was degraded, and only 10% of malathion was oxidised. In soil 30% of diazinon exposed to the sunlight was decomposed by photolysis, whereas in soil left in the darkness no degradation products were observed. In soil left under environmental conditions, 90% of diazinon was degraded and 40% from its initial concentration was transformed into IMP. The concentrations of the pesticides after 21 days on chicory were under maximal allowable concentration, which is 0.5 ppm for malathion and for diazinon. The concentration of malaoxon was more than twice as high as the allowable value, which is for the sum of malathion and malaoxon 3 ppm.     

Sorption and Desorption Behavior of Chloroanilines and Chlorophenols on Montmorillonite and Kaolinite

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.     

Time-dependent degradation and toxicity of diclofop-methyl in algal suspensions

Background, aim, and scope  As emerging contaminants, transformation products of the pollutants via various environmental processes are rather unknown, and some may predominately contribute to the environmental risks of the parent compounds. Hence, studies on transformation products complement the assessment of the environmental safety of the parent compounds. In this study, degradation experiments and toxicity tests using diclofop-methyl (DM), a widely used herbicide, and selected major transformation products were carried out in algal cultures to assess the time course of DM toxicity and its relevance in the formation of new breakdown products. Methods  The alga Chlorella vulgaris was maintained in the algal growth medium HB IV. The inhibition of algal growth was determined by measuring optical density at 680 nm (OD₆₈₀). Initially, DM and two selected breakdown products were added to the algal cultures, and following degradation experiments analyses were carried out by high performance liquid chromatography. In addition, the possible relationship between DM degradation and toxicity was assessed, based on physico-chemical properties of the compounds and their toxicity. Results  DM was rapidly absorbed onto the surface of the algal cells where it was hydrolyzed to diclofop (DC). Further degradation to 4-(2, 4-dichlorophenoxy) phenol (DP) occurred in the cells. However, only a minor amount of DC was degraded to DP under the same conditions when DC was initially added to the algal culture. When C. vulgaris was exposed to these compounds for 96 h, the determined EC₅₀ showed that DC was about ten times less toxic than DM (EC₅₀ = 0.42 mg/L) and that DP (EC₅₀ = 0.20 mg/L) was the most toxic. Discussion  Due to strong hydrophobicity and rare dissociation, DM has tendency toward absorption as compared to DC. The higher average degradation rates of DC initially treated by DM revealed the damage of the cell membranes caused by the DM and, thus, enhanced movement of DC into the cells. Following occurrence of phenolic breakdown products, DP suggested that DC should be intracellularly degraded to DP, which had a more potent mode of action and a higher acute toxicity. Moreover, the results for EC₅₀ at various intervals were in accordance with degradation processes of the initial compounds, in which rapid formation of DP was attributed to an increasing toxicity of DM. Conclusions  The toxicity of DM in algal suspensions increased with time due to its degradation to DP, which contributed significantly to the determined toxicity. These results indicate that the toxicity of the pesticide probably depends significantly on degradation. It is thus important to consider the time-dependent environmental processes when evaluating the toxicological effects of pesticides for proper risk assessment. Recommendations and perspectives  Increasing transformation products of these contaminants are identified in the environment, although they seem to be unknown in terms of the lacking studies on environmental behavior and ecotoxicity concerning them. Certain breakdown products probably greatly contribute to the apparent toxicity of the parent compounds, which is ascribed to the parent compounds in general studies ignoring the dependence of their toxicity on various transformation pathways. These studies that identify new intermediates and assess their toxicity via the environmental processes will be helpful to distinguish the nature of toxicity of the parent contaminants.     

Sorption and desorption behavior of chloroanilines and chlorophenols on montmorillonite and kaolinite

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.     

Toxicity profile of labile preservative bronopol in water: the role of more persistent and toxic transformation products

Transformation products usually differ in environmental behaviors and toxicological properties from the parent contaminants, and probably cause potential risks to the environment. Toxicity evolution of a labile preservative, bronopol, upon primary aquatic degradation processes was investigated. Bronopol rapidly hydrolyzed in natural waters, and primarily produced more stable 2-bromo-2-nitroethanol (BNE) and bromonitromethane (BNM). Light enhanced degradation of the targeted compounds with water site specific photoactivity. The bond order analysis theoretically revealed that the reversible retroaldol reactions were primary degradation routes for bronopol and BNE. Judging from toxicity assays and the relative pesticide toxicity index, these degradation products (i.e., BNE and BNM), more persistent and higher toxic than the parent, probably accumulated in natural waters and resulted in higher or prolonging adverse impacts. Therefore, these transformation products should be included into the assessment of ecological risks of non-persistent and low toxic chemicals such as the preservative bronopol.     

Toxicity of fenamiphos and its metabolites to the cladoceran Daphnia carinata: the influence of microbial degradation in natural waters

The acute toxicity of an organophosphorous pesticide, fenamiphos and its metabolites, fenamiphos sulfoxide, fenamiphos sulfone, fenamiphos phenol, fenamiphos sulfoxide phenol and fenamiphos sulfone phenol, to a cladoceran, Daphnia carinata was studied in both cladoceran culture medium and natural water collected from a local river. The toxicity followed the order: fenamiphos>fenamiphos sulfone>fenamiphos sulfoxide. The hydrolysis products of fenamiphos, F. sulfoxide (FSO) and F. sulfone (FSO(2)) (F. phenol, FSO phenol and FSO(2) phenol) were not toxic to D. carinata up to 500microgl(-1) water, suggesting hydrolysis reaction leads to detoxification. Also the toxicity was reduced in natural water compared to the cladoceran culture medium due to microbial mediated degradation of toxicants in the natural water. Fenamiphos and its metabolites were stable in both cladoceran water and filter-sterilised natural water while these compounds showed degradation in unfiltered natural water implicating the microbial role in degradation of these compounds. To our knowledge this is the first study on acute toxicity of fenamiphos metabolites to cladoceran and this study suggests that the organophosphate pesticides are highly toxic to fresh water invertebrates and therefore pollution with these compounds may adversely affect the natural ecosystems.     

Evaluation of HCH isomers and metabolites in soils, leachates, river water and sediments of a highly contaminated area

In this work we evaluate the contamination caused by HCH residues in the soil, leachates, river water and sediments of an industrial estate of the NW of Spain. We study the distribution of the isomers in the different matrices, analysing 37 soil samples, collected in eight points at several depths, six natural leachates, four river water samples and three river sediments. Soil and leachate samples present very high levels of HCH isomers, higher than the established by legislation, and some pesticides were also detected in the analysed river water whereas no pesticides were detected in the river sediments. The distribution of isomers was different depending on the matrix analysed. Some natural degradation products and also other organochlorine pesticides were detected in the samples analysed.     

Photocatalytic ozonation of pesticides in a fixed bed flow through UVA-LED photoreactor

In this study, a fixed bed flow through UVA-LED photoreactor was used to compare the efficiency of ozone, photocatalysis and photocatalysis-ozone degradation, and mineralization of two pure pesticides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), and a commercial one, Killex®. For the degradation of the parent compounds, ozone-based processes were more effective. While for mineralization, photocatalytic processes were more effective. Photocatalytic ozonation was the most efficient process for both the degradation and mineralization of the parent compounds. The degradation rates and mineralization by photocatalytic ozonation were higher than the summation of the corresponding rates by ozonation and photocatalysis, indicating a symbiotic relationship.Overall, the photocatalytic ozonation process with the fixed bed TiO₂ reduces the time needed for the degradation and mineralization of the pesticides, reduces the costs of powder catalyst separation and overcomes the reduced efficiency of immobilized catalysts, which makes the process quite attractive for practical applications.     

Interaction of phenanthrene and its primary metabolite (1-hydroxy-2-naphthoic acid) with estuarine sediments and humic fractions

Experiments were conducted to compare the sorption and desorption of phenanthrene and its primary degradation product, 1-hydroxy-2-naphthoic acid (HNA), in estuarine sediment, humic acid (HA) and humin. Ionic composition, ionic strength (0.4 M) and pH (7.6) were employed to mimic native estuarine pore water at the sediment-water interface. Sorption to whole sediment and organic matter (OM) fractions was significantly lower for HNA than for phenanthrene. Whereas HNA did not sorb to HA, uptake to sediment and humin was observed, suggesting that HNA does not bind directly to OM. Phenanthrene uptake was characterized by hysteretic behavior and exhibited slow desorption. In contrast, HNA initially was more readily desorbed from sediment and humic fractions, but a significant fraction was not recovered in repeated desorption runs. The lower sorption of HNA reflects its greater polarity and water solubility, but the consistent retention of a non-desorbing fraction suggests strong binding and/or chemical transformation reactions may be important. It was postulated that abiotic transformation of HNA may occur in estuarine sediments, in part due to the presence of redox active minerals (Fe(III) and Mn(IV) oxides). The presence of Fe and Mn solids in the estuarine sediment was verified by sequential extraction and studies were then conducted to investigate the transformation of HNA in the presence of synthetic goethite (alpha-FeOOH) and birnessite (delta-MnO2) as model solids. Reaction with birnessite led to transformation of all HNA in solution within 24 h and resulted in the formation of partial oxidation products (POPs). Following reaction with goethite, HNA was present in solution and POPs were observed in the weakly bound fraction. This study indicates that degradation products of polycyclic aromatic hydrocarbons (PAHs) may have distinctly different sorption affinities and reactivities toward environmental surfaces than their parent compounds.     

Occurrence of organophosphorus compounds in polluted marine sediments near a pesticide manufacturing plant

Sediment samples from 23 sampling stations in Nissum Broad (Jutland, Denmark) have been analysed for their contents of 8 organophosphorus compounds: 4 pesticides and 4 related triesters.Only in a few samples, all collected within a short distance from a pesticide manufacturing plant, detectable levels of organophosphates have been observed. The levels ranged from less than 1 μg/kg (ppb) up to 3, 8 mg/kg (ppm) for single compounds.One compound, triethylphosphate, occurred at low concentrations (<1 ppb) in many sediment samples independently of the distance from the chemical plant. Assumably, for this compound, other sources of pollution than the chemical plant may be considered.     

Measurement of pollution levels of organochlorine and organophosphorus pesticides in water, soil, sediment, and shrimp to identify possible impacts on shrimp production at Jiquilisco Bay

This study aims to identify levels of several organochlorine and organophosphorus compounds in shrimp-raising areas of coastal El Salvador, to assess potential impacts on shrimp growth and survival that hamper the sustainability of aquaculture in the region. The paper reports the current levels of γ-HCH, 4,4'-DDT, 4,4'-DDE, 4,4'-DDD, endrin, dieldrin, heptachlor, parathion, methyl parathion, and etoprophos in soils (depth 20 cm), sediments (depth 5 cm), shrimp (Penaeus sp.), and water of three rearing ponds and also in the sediment (depth 5 cm) and water surrounding those ponds in Jiquilisco Bay. Sampling was carried out during the dry (January-March) and rainy (June-August) seasons of 2008. The presence of pesticides in the samples of water, shrimp, and sediment at shrimp ponds was not detected in either season; however, in soil samples (depth 20 cm) taken from these ponds, heptachlor, endrin, dieldrin, 4,4'-DDD, and 4,4'-DDT were identified at concentrations below the method limit of quantification (LOQ), and 4,4'-DDE was found in a concentration falling in the range from 3.85 to 19.61 ng/g. In samples of water taken at the bay water intakes to the rearing ponds, we observed dieldrin concentrations in the range between 0.085 ng/mL and 0.182 ng/mL during the dry season. In the samples of sediments taken in the surrounding areas of shrimp ponds, we found-for both seasons-that in 60 % of the samples, 4,4'-DDE was present in concentrations ranging from 3.75 ng/g to 30.97 ng/g. Additionally, in the rainy season, we observed heptachlor in sediment at concentrations below the method quantification limit. It was concluded that organochlorine compounds from pesticides are still present in Jiquilisco Bay, trapped in deep sediment, even though they have been banned since the 1980s. These were not detected in shrimp tissue, surface water, and shallow sediment in rearing ponds, and hence, we do not believe their presence has any major impact on shrimp production in sampled areas.     

Chemical stability of chlortetracycline and chlortetracycline degradation products and epimers in soil interstitial water

Tetracyclines and tetracycline degradation products and epimers end up in the environment. In order to predict the persistence of the potential dominating species of the chlortetracyclines in the environment, the chemical stability of chlortetracycline (CTC) and four major CTC degradation products and epimers (iso-CTC, 4-epi-CTC, anhydro-CTC, and 4-epi-anhydro-CTC) was studied in milliQ water and soil interstitial water (SIW) under environmentally relevant conditions (oxygen, light, pH (3-9), and temperature (6 degrees C and 20 degrees C)). The chemical stability of the compounds was evaluated by following the decrease in amount of parent compound over time. In order to compare the results obtained under the varying conditions, apparent pseudo-first-order rate constants (k(obs)) for the disappearance of the parent compound and corresponding apparent half-lives were calculated. A statistical evaluation of the data showed that the chemical stability of the chlortetracyclines was generally dependent on photolysis, temperature, and matrix. The presence or absence of oxygen did not influence on the chemical stability. The presence of calcium and magnesium ions in SIW is believed to account for the significant differences in half-lives between milliQ water and SIW, although numerous of other factors are believed to influence as well. Generally, the five compounds were more persistent at pH 3-4 than at pH above 5.     

Distribution and fate of organochlorine pesticide residues in sediments from the selected rivers in Taiwan

The contamination of organochlorine pesticides (OCPs) in sediments from selected rivers in Taiwan was investigated to evaluate the pollution potentials and hazard in river sediments. Da-han River and Erh-jen River were selected as the target rivers due to their serious pollution. A total of 40 surface sediment samples were collected at five sampling stations along the rivers. Results showed that the concentrations of various pesticides in sediments were in the range of 0.57-14.1 ng/g for sigmaHCH, 0.05-0.15 ng/g for aldrin, 0.12-5.8 ng/g for dieldrin, 0.22-0.64 for endrin, 0.24-6.37 ng/g for endosulfan and 0.21-8.81 ng/g for EDDT (p,p'-DDD, p,p'-DDE, p,p'-DDT). Among the OCPs, sigmaHCH, endosulfan and sigmaDDT were the most dominant compounds in the river sediments. Endosulfan sulfate was the most frequent detected compound in the sediments from the selected rivers. Also, sigmaDDT, dieldrin and beta-HCH were in abundance. Different contamination patterns between the selected river sediments were also observed. Da-han River was mainly contaminated with endosulfan sulfate and sigmaDDT. Whereas the main pesticides in Erh-jen River were beta-HCH and sigmaDDT. Among the cyclodiene compounds, dieldrin was in abundance in most of the sediments. Moreover, the frequencies of detection of the metabolites were higher than those of parent compounds, depicting that the sediments have contaminated for a long time. The results obtained in this study showed that there still exist a variety of OCP residues in the river sediments in Taiwan.     

Study on the photodegradation of amidosulfuron in aqueous solutions by LC-MS/MS

Sulfonylurea herbicides are extensively widespread for the protection of a variety of crops and vegetables because of their low application rates, high selectivity and low persistency in the environment; unfortunately, their low persistence does not always correspond to a lower toxicity, since new species potentially more toxic and stable than the precursor herbicides can form, owing to natural degradation processes. Here, the photodegradation of amidosulfuron in aqueous solutions was studied by high-performance liquid chromatography with diode array detection and tandem mass spectrometry to identify the degradation products in order to outline the environmental fate of the molecules generating from the simulation of one of the natural processes that can occur, i.e., photoinduced degradation. The photodegradation process results in a first order kinetic reaction with a t _1/2 value of 276 h (11.5 days) and a kinetic constant of 0.0027 h^?1, and three possible degradation products were identified. The results obtained are then compared to those obtained in previous works carried out in comparable experimental conditions about nicosulfuron and tribenuron-methyl, two sulfonylurea herbicides belonging to different classes, and to literature data: hypotheses on the existence of preferential degradation pathways are then drawn, in consequence of the molecular structure of the sulfonylurea pesticide. In particular, the use of organic solvents to obtain complete solubilization of the sample plays a fundamental role and deeply influences the degradation processes that, therefore, not always fully adhere to the actual natural photodegradation pathways. Moreover, considerations about toxicity were driven since the complete mineralisation of the sample is not reached: even when the parent pesticides are totally degraded, they are, however, transformed into other organic compounds showing, if subject to ecotoxicological tests, at least the same toxicity of the precursor herbicides. The evidence here presented suggests that, at least for the class of sulfonylurea pesticides, their professed low persistence actually does not produce any real advantage.