Arsenic metabolism in marine bacteria and yeast

Arsenic metabolism was studied for two marine microorganisms, a facultative anaerobic bacterium, Serratia marinorubra, and an obligately aerobic yeast, Rhodotorula rubra. Both were cultivated in media with (⁷⁴As) arsenate (As V), and the products of arsenate metabolism were determined qualitatively. Both the bacterium and the yeast produced arsenite (AS III) and methylarsonic acid [CH₃AsO(OH)₂]. In addition to the foregoing, only the yeast produced dimethylarsinic acid (CH₃)₂AsO(OH) and volatile alkylarsines. In contrast, the bacterium growing anaerobically with cobalamine as a cofactor did not synthesize gaseous forms of arsenic such as methylarsines. Neither organism synthesized arsoniumphospholipids such as those produced by marine phytoplankton or terrestrial fungi. The yeast did not accumulate arsenite, but instead transported some of it into the culture medium and methylated the remainder first to methylarsonic acid and then to dimethylarsinic acid. Finally, the latter compound was methylated further and volatile alkylarsines were formed. In contrast, the bacterium retained all products of arsenate metabolism intracellularly. Both the bacterium and the yeast, therefore, converted relatively toxic arsenate, the most abundant arsenic compound in seawater, to products that were presumably less toxic.     

Role of Acinetobacter sp. in arsenite As(III) oxidation and reducing its mobility in soil

Microbial arsenite oxidation was observed by Acinetobacter sp. XS21, this strain oxidised arsenite As(III) up to 80?mM within 48–72?h of incubation. The present strain XS21 oxidised As(III) at a very high concentration in a shorter interval of time than any of the previous reported microbes. Further, XS21 was applied to the soil to observe its ability in reducing the mobility of As(III), and we found that Acinetobacter sp. XS21 efficiently removed arsenite from soluble-exchangeable fraction and removed 70% of the arsenite as compared to control. This feature makes it a potential candidate for bioremediation. Arsenic-resistant bacteria with strong As(III)-oxidising ability may have potential to improve bioremediation of As(III)-contaminated sites. To understand their basis of resistance and transformation we found the As(III) oxidase gene using degenerate primer and amplified ～550?bp of aioA gene. Amplified aioA gene sequence exhibiting 52% identity in terms of gene and deduced protein sequence to Uncultured bacterium, and Achromobacter sp. arsenite oxidase of larger subunit. Arsenite oxidase, an enzyme, was also observed in this isolate, which may provide a resistance and transforming ability. This bacterium was identified as Acinetobacter sp., by sequencing 16s rRNA gene sequence analysis.     

Distribution of arsenic compounds in Plantaginaceae and Cyperaceae plants growing in contaminated soil

The ability of plant species to accumulate arsenic (As) species in the biomass from As-contaminated soils is variable. Among the plants widely grown at the As-contaminated locations, Plantaginaceae and Cyperaceae families belong to the frequent ones. In this study, the ability of Plantago lanceolata (Plantaginaceae) and three wetland plant species representing the family Cyperaceae (Carex praecox, Carex vesicaria, and Scirpus sylvaticus) naturally occurring in the soils with an elevated As in the Czech Republic were investigated. The plants were cultivated under controlled conditions in an As-contaminated soil reaching 735?mg?kg^?1 of the total As. The total As in plants reached up to 8.3?mg?kg^?1 in leaves, and up to 155?mg?kg^?1 in roots of C. praecox. Dominant As compounds were arsenite and arsenate with a small abundance of dimethylarsinic acid (DMA) in all the plant species. In Cyperaceae, small percentages of arsenobetaine (AB) and arsenocholine (AC) were detected, suggesting the ability of these plants to transform As into less toxic compounds. Moreover, the important role of As(V) sequestration on iron plaque on the root surface of Cyperaceae was confirmed. In this context, root washing with oxalic acid partially disrupted the iron plaque for the better release of arsenate.     

Arsenic speciation in polychaetes (Annelida) and sediments from the intertidal mudflat of Sundarban mangrove wetland, India

This paper documents the concentration of total arsenic and individual arsenic species in four soft-bottom benthic polychaetes (Perenereis cultifera, Ganganereis sootai, Lumbrinereis notocirrata and Dendronereis arborifera) along with host sediments from Sundarban mangrove wetland, India. An additional six sites were considered exclusively for surface sediments for this purpose. Polychaetes were collected along with the host sediments and measured for their total arsenic content using inductively coupled plasma mass spectrometry. Arsenic concentrations in polychaete body tissues varied greatly, suggesting species-specific characteristics and inherent peculiarities in arsenic metabolism. Arsenic was generally present in polychaetes as arsenate (As^V ranges from 0.16 to 0.50 mg kg^?1) or arsenite (As^III ranges from 0.10 to 0.41 mg kg^?1) (30–53 % as inorganic As) and dimethylarsinic acid (DMA^V <1–25 %). Arsenobetaine (AB < 16 %), and PO₄-arsenoriboside (8–48 %) were also detected as minor constituents, whilst monomethylarsonic acid (MA^V) was not detected in any of the polychaetes. The highest total As (14.7 mg kg^?1 dry wt) was observed in the polychaete D. arborifera collected from the vicinity of a sewage outfall in which the majority of As was present as an uncharacterised compound (10.3 mg kg^?1 dry wt) eluted prior to AB. Host sediments ranged from 2.5 to 10.4 mg kg^?1 of total As. This work supports the importance of speciation analysis of As, because of the ubiquitous occurrence of this metalloid in the environment, and its variable toxicity depending on chemical form. It is also the first work to report the composition of As species in polychaetes from the Indian Sundarban wetlands.     

Field based speciation of arsenic in UK and Argentinean water samples

A field method is reported for the speciation of arsenic in water samples that is simple, rapid, safe to use beyond laboratory environments, and cost effective. The method utilises solid-phase extraction cartridges (SPE) in series for selective retention of arsenic species, followed by elution and measurement of eluted fractions by inductively coupled plasma mass spectrometry (ICP-MS) for “total” arsenic. The method is suitable for on-site separation and preservation of arsenic species from water. Mean percentage accuracies (n = 25) for synthetic solutions of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA), and dimethylarsinic acid (DMA) containing 10 μg l⁻¹ As, were 98, 101, 94, and 105%, respectively. Data are presented to demonstrate the effect of pH and competing anions on the retention of the arsenic species. The cartridges were tested in the UK and Argentina at sites where arsenic was known to be present in surface and groundwaters, respectively, at elevated concentrations and under challenging matrix conditions. In Argentinean groundwater, 4–20% of speciated arsenic was present as MA and 20–73% as As^III. In UK surface waters, speciated arsenic was measured as 7–49% MA and 12–42% DMA. Comparative data from the field method using SPE cartridges and the laboratory method using liquid chromatography coupled to ICP-MS for all water samples provided a correlation of greater than 0.999 for As^III and DMA, 0.991 for MA, and 0.982 for As^V (P < 0.01).     

植物砷吸收与代谢的研究进展

砷(As)作为一种植物非必需的类金属元素广泛存在于自然界中,砷过量摄人不仅会对植物生长产生毒害作用,而且在植物的可食部位累积并通过食物链对人体健康构成威胁.生长介质中的砷酸盐(五价砷)一般是通过磷酸盐转运蛋白被植物吸收的,而亚砷酸(三价砷)和没有解离的甲基化砷则主要是通过质膜上的水通道蛋白被植物吸收的.在植物体内五价砷...     

Arsenic detoxification potential of <Emphasis Type="Italic">aox</Emphasis> genes in arsenite-oxidizing bacteria isolated from natural and constructed wetlands in the Republic of Korea

Arsenic is subject to microbial interactions, which support a wide range of biogeochemical transformations of elements in natural environments such as wetlands. The arsenic detoxification potential of the bacterial strains was investigated with the arsenite oxidation gene, aox genotype, which were isolated from the natural and constructed wetlands. The isolates were able to grow in the presence of 10 mM of sodium arsenite (As(III) as NaAsO₂) and 1 mM of d+glucose. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that these isolated strains resembled members of the genus that have arsenic-resistant systems (Acinetobacter sp., Aeromonas sp., Agrobacterium sp., Comamonas sp., Enterobacter sp., Pantoea sp., and Pseudomonas sp.) with sequence similarities of 81–98%. One bacterial isolate identified as Pseudomonas stutzeri strain GIST-BDan2 (EF429003) showed the activity of arsenite oxidation and existence of aoxB and aoxR gene, which could play an important role in arsenite oxidation to arsenate. This reaction may be considered as arsenic detoxification process. The results of a batch test showed that P. stutzeri GIST-BDan2 (EF429003) completely oxidized in 1 mM of As(III) to As(V) within 25–30 h. In this study, microbial activity was evaluated to provide a better understanding of arsenic biogeochemical cycle in both natural and constructed wetlands, where ecological niches for microorganisms could be different, with a specific focus on arsenic oxidation/reduction and detoxification.     

Effect of arsenic compounds on Vibrio fischeri light emission and butyrylcholinesterase activity

The effect of organic arsenic compounds and inorganic As(V) and As(III) on Vibrio fischeri luminescence and butyrylcholinesterase activity were evaluated using Microtox and microcalorimetric analysis. Organic arsenic compounds were arsenocholine (AsC), arsenobetaine (AsB), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and the antibiotic 4-hydroxy-3-nitrobenzene arsonic acid (HNAA, Roxarsone^(R)). HNAA, As(III) and As(V) were found to inhibit Vibrio fischeri light emission whereas MMA, DMA, AsC and AsB produced only a slight effect. By contrast, only AsC, AsB and As(III) were found to inhibit butyrylcholinesterase activity. Selected article from the 6th European Meeting on Environmental Chemistry, University of Belgrade, Serbia and Montenegro organized by Prof. Dr. Branimir Jovancicevic (www.research.plymouth.ac.uk/ace).     

Formation of dimethyldithioarsinic acid in a simulated landfill leachate in relation to hydrosulfide concentration

Dimethyldithioarsinic acid (DMDTA^V), present in such intense sources as municipal landfill leachate, has drawn a great deal of attention due to its abundant occurrence and different aspect of toxicity. The hydrosulfide (HS⁻) concentration in leachate was studied as a major variable affecting the formation of DMDTA^V. To this end, the HPLC–ICPMS system equipped with the reversed-phase C18 column was used to determine DMDTA^V. Simulated landfill leachates (SLLs) were prepared to cover a mature landfill condition with the addition of sodium sulfate and sulfide at varying concentrations in the presence of dimethylarsinic acid (DMA^V). The concentration of sodium sulfide added in the SLLs generally exhibited a strong positive correlation with the concentration of DMDTA^V. As such, the formation of DMDTA^V in the SLLs is demonstrated to be controlled by the interactive relationship between DMA^V and the HS⁻.

     

Chromium binding by calf thymus nuclei and effects on chromatin

1. No binding of chromium was detected after incubation of calf thymus nuclei with hexavalent chromium up to 0.5 mM.

2. Chromium was readily taken up and tightly bound after incubation with trivalent chromium.

3. In a DNA‐filter binding assay, increasing amounts of chromium and DNA were bound with increasing chromium trichloride concentrations incubated with the nuclei.

4. Treatment with proteinase K abolished the increase in DNA retention induced by trivalent chromium.

5. It is concluded that trivalent chromium is the ultimate genetoxic agent after chromate uptake by living cells.

     

Species-level study on arsenic availability from dietary components

Arsenic (As) contaminated water and foodstuffs are of major concern. Samples of drinking–cooking water (n = 50), raw rice (n = 50), common vegetables (eight types), and common pulses (three types) were collected from households in the endemic region. The study found up to 70% As reduction by using safe water for cooking of rice and vegetables. Speciation study reflected more arsenate than arsenite and other organic arsenicals in all the types of samples. Male intake of 293 μg As through drinking water contained 38 μg arsenite and 246 μg arsenate, and female intake of 199 μg As contained 167 μg arsenate and 25 μg arsenite. In cooked rice, 108 μg As contained 69 μg arsenate and 17 μg arsenite with 9 μg dimethylarsonic acid (DMA). Total As consumption from cooked vegetables was 45 μg with 34 and 4 μg of arsenite and arsenate, respectively, and 5 μg of DMA. Data indicate that cooking with As-free water removes arsenic in already contaminated foodstuffs but without interconversion of the As species, from toxic inorganic to less toxic organic forms.     

In vitro effects of lead on fatty acid composition,oxidative stress biomarkers and quality of ram spermatozoa

The sperm quality and several parameters associated with oxidative stress were evaluated in ram (Ovis aries) spermatozoa suspensions incubated with 0, 50 or 500 ng/mL Pb during 0, 1, 3 or 6 h. The presence of Pb during incubation, reduced the integrity of the acrosome, % sperm motility and integrity, and the functionality of membrane. On the contrary, % polyunsaturated fatty acids and the activities of glutathione peroxidase and superoxide dismutase in the spermatozoa suspensions were not affected by Pb. Moreover, glutathione peroxidase activity was decreased and the fatty acid composition changed due to the relative increase in % stearic acid during the incubation time independently on Pb presence. Data showed that several effects of Pb on sperm quality usually observed in vivo also occurred in vitro, but without any relationship with oxidative stress biomarkers.     

Enzymatic and cellular level effects of chromium∗

Exposure of Cr to four hepatic enzymes activities of tilapia, viz. acid‐ and alkaline phosphatases, catalase and glucose‐6‐phosphatase, was contrary to the results obtained for Cd and Ni. This is the only heavy metal investigated thus far that dramatically augmented glucose‐6‐phosphatase by approximately 83% at a concentration of 12 mg L^‐1 in vivo in lieu of the fact of an initial inhibition of approximately 45 % at a lower concentration of Cr; 6 mg L^‐1. In the case of acid phosphatase and catalase activities progressive increment was observed up to 50 and 217% respectively at a concentration of 12 mg L^‐1 Cr. On the other hand, in contrast to all the investigated enzymes interestingly alkaline phosphatase was inhibited continuously at all concentrations up to 46% at 12 mgL^‐1 Cr. In vitro experiments were contrary to the above mentioned results, whereby all hepatic enzymes were inhibited with major inhibition observed for acid phosphatase of approximately 60% from 5 mgL^‐1 Cr onwards in the system.

At cellular level, Cr exposure at a lethal dose of 12 mgL^‐1 demonstrated similar effects to that of Cd. In general, the glycogen and fat reserves were depleted while lysosomal activity is increased. As compared to the effects of Cd, the mitochondria did not indicate any prominent reflection in the formation of intramitochondrial bodies. Further, similar to Cd, the cell membrane as well as nucleus were not affected.     

Study of Fishes in the Chung-Kung Stream: Species Distribution and Organochlorine Pesticide Residues

Abstract

In this study, we investigated the potential for reductive dechlorination of 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) by municipal sewage sludge adapted to 2,4-DCP at different concentrations. 2,4-DCP was completely dechlorinated within 4 weeks. After 18 weeks' incubation, 2,4,6-TCP was also completely dechlorinated and the residue of PCP was 0, 44.46, 51.96% at 0.5, 5, and 50 μg ml¹ respectively. the 2,4-DCP adapted communities initially removed the ortho-chlorine from PCP of 5.0, 50 μg ml¹, following an ortho < para < meta order of chlorine removal. Intermediate products were 3,4,5-TCP, 3,5-DCP, 3-CP (3-chlorophenol), phenol, benzoate and hexanoic acids, whereas PCP (0.5 μg ml¹) indicated a preference for meta-chlorine removal. the intermediate product of 2,4,6-TCP at three concentrations were 2,4-DCP, phenol, benzoate and hexanoic acid. These products were identified by GC-MASS spectrometry. the effects of supplements, including sodium citrate (0.08 mM), sodium pyruvate (0.18 mM), sodium sulphate (0.14 mM) had a direct stimulatory effect on the dechlorination of 2,4,6-TCP and PCP after treatment for 4 weeks, but dechlorination was inhibited after 8 weeks.     

Arsenic contamination of natural waters in San Juan and La Pampa, Argentina

Arsenic (As) speciation in surface and groundwater from two provinces in Argentina (San Juan and La Pampa) was investigated using solid phase extraction (SPE) cartridge methodology with comparison to total arsenic concentrations. A third province, Río Negro, was used as a control to the study. Strong cation exchange (SCX) and strong anion exchange (SAX) cartridges were utilised in series for the separation and preservation of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA^V) and dimethylarsinic acid (DMA^V). Samples were collected from a range of water outlets (rivers/streams, wells, untreated domestic taps, well water treatment works) to assess the relationship between total arsenic and arsenic species, water type and water parameters (pH, conductivity and total dissolved solids, TDS). Analysis of the waters for arsenic (total and species) was performed by inductively coupled plasma mass spectrometry (ICP-MS) in collision cell mode. Total arsenic concentrations in the surface and groundwater from Encon and the San José de Jáchal region of San Juan (north-west Argentina within the Cuyo region) ranged from 9 to 357 μg l^?1 As. Groundwater from Eduardo Castex (EC) and Ingeniero Luiggi (LU) in La Pampa (central Argentina within the Chaco-Pampean Plain) ranged from 3 to 1326 μg l^?1 As. The pH range for the provinces of San Juan (7.2–9.7) and La Pampa (7.0–9.9) are in agreement with other published literature. The highest total arsenic concentrations were found in La Pampa well waters (both rural farms and pre-treated urban sources), particularly where there was high pH (typically > 8.2), conductivity (>2,600 μS cm^?1) and TDS (>1,400 mg l^?1). Reverse osmosis (RO) treatment of well waters in La Pampa for domestic drinking water in EC and LU significantly reduced total arsenic concentrations from a range of 216–224 μg l^?1 As to 0.3–0.8 μg l^?1 As. Arsenic species for both provinces were predominantly As^III and As^V. As^III and As^V concentrations in San Juan ranged from 4–138 μg l^?1 to <0.02–22 μg l^?1 for surface waters (in the San José de Jáchal region) and 23–346 μg l^?1 and 0.04–76 μg l^?1 for groundwater, respectively. This translates to a relative As^III abundance of 69–100% of the total arsenic in surface waters and 32–100% in groundwater. This is unexpected because it is typically thought that in oxidising conditions (surface waters), the dominant arsenic species is As^V. However, data from the SPE methodology suggests that As^III is the prevalent species in San Juan, indicating a greater influence from reductive processes. La Pampa groundwater had As^III and As^V concentrations of 5–1,332 μg l^?1 and 0.09–592 μg l^?1 for EC and 32–242 μg l^?1 and 30–277 μg l^?1 As for LU, respectively. Detectable levels of MA^V were reported in both provinces up to a concentration of 79 μg l^?1 (equating to up to 33% of the total arsenic). Previously published literature has focused primarily on the inorganic arsenic species, however this study highlights the potentially significant concentrations of organoarsenicals present in natural waters. The potential for separating and preserving individual arsenic species in the field to avoid transformation during transport to the laboratory, enabling an accurate assessment of in situ arsenic speciation in water supplies is discussed.     

Mechanistic aspects of the thermal formation of halogenated organic compounds including polychlorinated dibenzo‐p‐dioxins. Part IV†: Incorporation of inorganic chlorine into organic matter and thermochemical aromatizations

The pyrolysis and chlorination of petroleum coke in a NaCl‐KCl melt results in the production of CCl₄ and C₆Cl₆. Polychlorinated dibenzo‐p‐dioxins (PCDDs) are produced from the air oxidation and chlorination of coal using HCl or Cl₂. Smoking of tobacco containing ³⁶Cl^e provides CH₃ ³⁶Cl.

At 350°C, the rateof aromatization of 1,3‐cyclohexadiene is negligible as compared to that of 1,4‐cyclohexadiene. The aromatization of the latter diene proceeds through the molecular elimination of hydrogen; while that of 1,3‐cyclohexadiene expecially at higher pressure (10–90 Torr) and at 362–421 °C involves free radical chain mechanism.     

Degradation profile of azoxystrobin in Andisol soil: laboratory incubation

The fate of azoxystrobin in soil under the effect of different temperature is of interest because application directions specify soil-surface treatments for number of agricultural pests. Temperature is an important factor governing the rate of degradation in soil pore. The purpose of this investigation was to understand better the effect of temperature on the degradation of azoxystrobin in Japanese Andisol soil. This was done through laboratory incubation of soil at three different temperatures (5 °C, 20 °C, 35 °C). First-order kinetics could be used to describe degradation of azoxystrobin under controlled condition of temperature (r² ? 94). The results showed that, during the 120-day incubation period for azoxystrobin, 64%, 70%, and 78% of applied azoxystrobin were degraded at 5 °C, 20 °C, and 35 °C, respectively. By using the Arrhenius equation, the activation energy of degradation of azoxystrobin fungicide was calculated (7.48 ± 1.74 kJ mol^?1) in soils, which confirm that temperature had a significant influence on the degradation rate. Q₁₀ value of 1.11, for azoxystrobin, indicated that the response of fungicide dissipation to temperature was large. For azoxystrobin, there was a much larger difference in dissipation rates at 5 °C and 35 °C, indicating that biological and/or chemical degradation of azoxystrobin may have nearly reached its optimum at 35 °C.     

Accumulation of arsenic from water and food by Littorina littoralis and Nucella lapillus

The mechanism, and factors influencing the process of arsenic accumulation and elimination in a food chain [Fucus spiralis (L.) Littorina littoralis (L.) Nucella lapillus (L.)] were examined using the radioisotope ⁷⁴As. Organisms were collected during 1978 from the estuary of Restronguet. Creek in southwest England. Arsenate uptake by L. littoralis increased linearly with increasing external arsenate concentration up to ca. 500 g 1^-1 but was independent at higher arsenate concentrations. Arsenic uptake by L. littoralis was suppressed by metabolic inhibition (potassium cyanide) and lowered salinity. At 26°C, arsenic uptake was twice that at 10°C. L. littoralis accumulated 1o times more arsenic from solution than N. lapillus. Approximately 91% of ⁷⁴As accumulated from water by L. littoralis was found in the soft tissues, especially the digestive gland and gonads, but in N. lapillus 85% was associated with the shell. Arsenate uptake was twice that of arsenite in L. littoralis. Phosphate at normal environmental levels (2.4 M) did not influence the accumulation of arsenic by L. littoralis, although concentration-dependent inhibition of arsenic uptake was found between 8 and 17 M. Compared with macroalgae, the marine snails exhibit a much greater ability for eliminating arsenic. In L. littoralis the elimination of ⁷⁴As absorbed from sea water occurred in three stages, each contining equal amounts of the initial ⁷⁴As pool, with biological half-lives of 4, 13 and 47 d. A biphasic pattern of elimination was found for food-labelled snails (L. littoralis and N. lapillus). The rapid compartment, contributing a third of the arsenic, had a half-life of 4 d, while that of the slow compartment was 12 to 13 d. Fed snails eliminated arsenic more rapidly and extensively than starved individuals. All arsenic in the tissues of the snails studied was available for exchange with that in the environment. The diet is by far the major source of arsenic in L. littoralis and N. lapillus, which appear equally efficient at assimilating arsenic from food.     

Removal of arsenic by Acidothiobacillus ferrooxidans bacteria in bench scale fixed-bed bioreactor system

In the present study arsenic contaminated simulated water and groundwater was treated by the combination of biological oxidation of tri-valent arsenite [As (III)] to penta-valent arsenate [As (V)] in presence of Acidothiobacillus ferrooxidans bacteria and its removal by adsorptive filtration in a bioreactor system. This method includes the immobilisation of A.ferrooxidans on Granulated Activated Carbon (GAC) capable of oxidising ferrous [Fe (II)] to ferric [Fe (III)]. The Fe (III) significantly converts the As (III) to As (V) and ultimately removed greater than 95% by the bed of GAC, limestone, and sand. The significant influence of Fe (II) concentration (0.1–1.5?gL^?1), flowrate (0.06–0.18?Lh^?1), and initial As (III) concentration (100–1000?µgL^?1) on the arsenic removal efficiency was investigated. The simulated water sample containing the different concentration of As (III) and other ions was used in the study. The removal of other co-existing ions present in contaminated water was also investigated in column study. The concentration of arsenic was found to be <10?µgL^?1 which is below Maximum Contaminant Level (MCL) as per WHO in treated water. The results confirmed that the present system including adsorptive-filtration was successfully used for the treatment of contaminated water containing As (III) ions.     

Prevalence of organochlorine pesticide residues in groundwaters of Kasargod District,India

The Kasargod District is the northernmost district of Kerala State and is bound between the north latitudes 12°02′27″ and 12°47′35″ and east longitudes 74°51′54″ and 75°25′25″. The present study highlights the contamination levels of organochlorine pesticides in open wells of the Kasargod District from 2010 to 2011. Maximum contamination of organochlorine pesticides (OCP's) was observed for endosulfan followed by hexachlorobenzene (BHC). Contamination levels of α-endosulfan were higher at Panathur (58?µg?L^?1) and next to Periya (37?µg?L^?1) in the postmonsoon season of 2010. During premonsoon 2011, the residue levels of α-endosulfan were higher at Panathady (56?µg?L^?1) followed by Rajapuram (40?µg?L^?1). Contamination levels of the BHC isomers exhibit the order of γ-BHC?>?α-BHC?>?β‐BHC, showing that γ-BHC represents 62% of the total OCP residues in premonsoon 2010. Among the studied OCP's, concentration levels of DDT were below detection limit. Maximum concentrations of the sum of all OCP residues were observed at Mulleria and Cheemeni (premonsoon 2010), followed by Panathur and Periya (postmonsoon 2010), and lowest in Panathady and Rajapuram (premonsoon 2011). Residues of OCP's were lowest in Paettikundu and Cheravatur in all the three seasons.