Fate of (14)C-labeled soybean and corn pesticides in tropical soils of Brazil under laboratory conditions

Evaluation of temperature corrections for pesticide half-lives in tropical and temperate soils

Temperature is a key factor that influences pesticide degradation. Extrapolating degradation half-lives (DT50) measured at a given temperature to different temperatures remains challenging, especially for tropical conditions with high temperatures. In this study, the use of the standard Arrhenius equation for correcting temperature effects on pesticide degradation in soils was evaluated and its performance was compared with that of alternative Arrhenius-based equations. To do so, a database of 509 DT50 values measured between 5 and 35 °C for 32 pesticides on tropical and temperate soils was compiled for the first time through an extensive literature search. The temperature correction models were fitted to the database using linear mixed regression approaches that included soil type and compound effects. No difference in the temperature dependence of DT50 between tropical and temperate soils was detected, regardless of the model. A comparison of the prediction performances of the models showed that constant activation energy (E_a) cannot be considered valid for the whole range of temperatures. The classical Arrhenius equation with an E_a of 65.4 kJ.mol^-1, as recommended by the European Food Safety Authority (EFSA), was shown to be valid for correcting the DT50 only for temperatures ranging from 5 to 20 °C. However, for temperatures greater than 20 °C, which are common in tropical environments, the median E_a was significantly lower at 10.3 kJ.mol^-1. These findings suggest the need to adapt the standard temperature correction of the European pesticide risk assessment temperature procedure when it is applied in tropical settings.

Influence of temperature on the toxicity of the elutriate from a pesticide contaminated soil to two cladoceran species

Brazil has become one of the largest consumers of pesticides in the world. However, there are still few studies evaluating pesticide toxicity integrating local aquatic and terrestrial environments. In addition, there is growing concern about the influence of temperature conditions related with climate change on contaminants toxicity. The aim of the present study was to evaluate the elutriate toxicity of the insecticide Kraft^® 36 EC (a.i. abamectin), the fungicide Score^® 250 EC (a.i. difenoconazole) and their mixture to the cladocerans Ceriodaphnia silvestrii and Daphnia similis, using model ecosystems (mesocosms). To this end, mesocosms were filled with natural soil and subjected to the following treatments: Control (Milli-Q water), Kraft (10.8 g abamectin ha^-1), Score (20 g difenoconazole ha^-1), and Kraft + Score (10.8 g abamectin ha^-1 + 20 g difenoconazole ha^-1). The experiment lasted 18 days, and the applications were made on days 1, 8, and 15; the occurrence of rainfall was simulated on days 1, 8, and 15 after applications and only rainfall simulation on days 4, 11, and 18. The experiment was conducted under two different temperatures: 23 °C and 33 °C. At 23 °C, single Kraft treatment and in combination with Score showed high toxicity to both cladocerans. At 33 °C, elutriate of the Kraft^® and mixture treatments were highly toxic to D. similis but not to C. silvestrii. The results indicate that while Kraft had higher toxicity than Score to both cladocerans, this toxicity was counteracted at 33 °C only for the exotic species, D. similis. The results portray the complexity of pesticide toxicity when considering realistic experimental settings including different organisms and temperature treatments.

Reducing the Environmental Risk of Chlorpyrifos Application through Appropriate Agricultural Management: Evidence from Carbon-14 Tracking

Chlorpyrifos (CPF) is one of the most critical insecticides in the world. However, many countries are gradually banning its use due to its reported hazardous impacts on humans. This study explored the possibility of reducing the environmental risk of CPF through appropriate agricultural management practices. Results showed that the environmental risk of CPF is lower under drainage conditions because there is more mineralization and less bound residues (BRs) than under submerged conditions. Bioaugmentation significantly enhanced the CPF mineralization and inhibited the formation of CPF-BRs. Biochar adsorbed CPF and thus reduced its bioavailability, but it could not completely eliminate the toxicity of CPF. In addition, bioaugmentation did not significantly affect the native microbial community of CPF-contaminated soil, suggesting its safety in reducing the environmental risk of CPF. The study indicated that the environmental risk of CPF could be reduced by appropriate agricultural management such as water management, bioaugmentation, soil biochar amendment, and selecting suitable soil types.

Enhanced mineralization of chlorpyrifos bound residues in soil through inoculation of two synergistic degrading strains

Bioaugmentation methods are frequently employed for pesticide pollution remediation; however, it is not clear whether the introduced bacteria affect the pesticide bound residue (BRs) composition and whether the BRs can be catabolized by the introduced strains. This study aimed at answering these questions by using ¹⁴C-chlorpyrifos (¹⁴C-CPF) and two CPF-degrading strains (Pseudomonas sp. DSP-1 and Cupriavidus sp. P2). The results showed that the BRs can be up to 83.0%, and that the CPF-BRs formed can be further transformed into ¹⁴CO₂ by the strains. Indeed, the microbial inoculation can increase the CPF mineralization by 1.0-22.1 times and can decrease the BRs by up to ~50% of the control (on day 20). Compared with the control without bioaugmentation, microbial inoculation enhanced the release of BRs by 2.2-18.0 times. Adding biochar to the soil can greatly inhibit CPF mineralization and maintain the BR content at a relatively stable level. The CPF residue can affect the composition of the indigenous soil microbial community, but the introduction of bacteria for remediation did not have a significant effect. The results indicate that Pseudomonas sp. DSP-1 and Cupriavidus sp. P2 are useful for remediating both CPF extractable and bound residues.

Acute and chronic toxicity of the fungicide carbendazim to the earthworm Eisenia fetida under tropical versus temperate laboratory conditions

Research efforts into the potential side-effects of pesticides on beneficial organisms have focused on temperate test species and conditions. There is thus a need for studies into the ecotoxicity of a vaster range of pesticides under tropical conditions. The present study therefore aimed to compare the acute and chronic toxicity of the fungicide carbendazim to the earthworm Eisenia fetida under tropical and temperate conditions. To this end, laboratory toxicity tests were conducted with a tropical and European strain of E. fetida, using different artificial (OECD and TAS) and natural (LUFA and TNS) soils, and under different test temperatures (20 °C and 28 °C). In the acute lethality tests with artificial soils, the tropical strain of E. fetida was three to four order of magnitude less sensitive than the European strain, which is ascribed to the higher test temperature and (hence) higher microbial activity/pesticide degradation. The tropical strain was particularly sensitive in the tropical natural soil, which was attributed to the low pH (3.9) of this soil. The chronic toxicity tests overall also showed a lower sensitivity of the tropical strain on reproduction. These findings thus support the use of toxicity data generated under temperate conditions in tropical pesticide effect assessments. However, intensive agricultural practices in the tropics may dictate that exposure levels (and hence potentially also risks) are higher.

Environmental risk assessment of pesticides in tropical terrestrial ecosystems: Test procedures, current status and future perspectives

Despite the increasing use of pesticides in tropical countries, research and legislative efforts have focused on their temperate counterparts. This paper presents a review of the literature on environmental risk assessment of pesticides for tropical terrestrial agroecosystems. It aims at evaluating potential differences in pesticide risk between temperate and tropical regions as well as to highlight research needs in the latter. Peculiarities of pesticide risks in tropical terrestrial agroecosystems are discussed in subsections 1) agricultural practices; 2) research efforts; 3) fate and exposure; 4) toxicity testing methods; and 5) sensitivity. The intensive and often inadequate pesticide application practices in tropical areas are likely to result in a relatively greater pesticide exposure in edge-of-field water bodies. Since pesticide fate may be different under tropical conditions, tropical scenarios for models estimating predicted environmental pesticide concentrations should be developed. Sensitivity comparisons do not indicate a consistent similar, greater or lower relative sensitivity of tropical soil organisms as compared to temperate organisms. However, several methods and procedures for application in the tropics need to be developed, which include: 1) identifying and collecting natural soils to be used as reference test substrates in tests; 2) identifying and discerning the range of sensitivity of native test species to soil contaminants; 3) developing test guidelines applicable to tropical/subtropical conditions; and 4) developing methods and procedures for higher tier testing for full development and implementation of environmental risk assessment schemes.

Quantifying the contribution of riparian soils to the provision of ecosystem services

Riparian areas, the interface between land and freshwater ecosystems, are considered to play a pivotal role in the supply of regulating, provisioning, cultural and supporting services. Most previous studies, however, have tended to focus on intensive agricultural systems and only on a single ecosystem function. Here, we present the first study which attempts to assess a wide range of ecological processes involved in the provision of the ecosystem service of water quality regulation across a diverse range of riparian typologies. Specifically, we focus on 1) evaluating the spatial variation in riparian soils properties with respect to distance with the river and soil depth in contrasting habitat types; 2) gaining further insights into the underlying mechanisms of pollutant removal (i.e. pesticide sorption/degradation, denitrification, etc.) by riparian soils; and 3) quantify and evaluate how riparian vegetation across different habitat types contribute to the provision of watercourse shading. All the habitats were present within a single large catchment and included: (i) improved grassland, (ii) unimproved (semi-natural) grassland, (iii) broadleaf woodland, (iv) coniferous woodland, and (iv) mountain, heath and bog. Taking all the data together, the riparian soils could be statistically separated by habitat type, providing evidence that they deliver ecosystem services to differing extents. Overall, however, our findings seem to contradict the general assumption that soils in riparian area are different from neighbouring (non-riparian) areas and that they possess extra functionality in terms of ecosystem service provision. Watercourse shading was highly habitat specific and was maximal in forests (ca. 52% shade cover) in comparison to the other habitat types (7-17%). Our data suggest that the functioning of riparian areas in less intensive agricultural areas, such as those studied here, may be broadly predicted from the surrounding land use, however, further research is required to critically test this across a wider range of ecosystems.

Dissipation and adsorption of isoproturon, tebuconazole, chlorpyrifos and their main transformation products under laboratory and field conditions

Assessment of dissipation constitutes an integral part of pesticides risk assessment since it provides an estimate of the level and the duration of exposure of the terrestrial ecosystem to pesticides. Within the frame of an overall assessment of the soil microbial toxicity of pesticides, we investigated the dissipation of a range of dose rates of three model pesticides, isoproturon (IPU), tebuconazole (TCZ), and chlorpyrifos (CHL), and the formation and dissipation of their main transformation products following a tiered lab-to-field approach. The adsorption of pesticides and their transformation products was also determined. IPU was the least persistent pesticide showing a dose-dependent increase in its persistence in both laboratory and field studies. CHL dissipation showed a dose-dependent increase under laboratory conditions and an exact opposite trend in the field. TCZ was the most persistent pesticide under lab conditions showing a dose-dependent decrease in its dissipation, whereas in the field TCZ exhibited a biphasic dissipation pattern with extrapolated DT90s ranging from 198 to 603.4days in the ×1 and ×2 dose rates, respectively. IPU was demethylated to mono- (MD-IPU) and di-desmethyl-isoproturon (DD-IPU) which dissipated following a similar pattern with the parent compound. CHL was hydrolyzed to 3,5,6-trichloro-2-pyridinol (TCP) which dissipated showing a reverse dose-dependent pattern compared to CHL. Pesticides adsorption affinity increased in the order IPU<TCZ<CHL. IPU transformation products showed low affinity for soil adsorption, whereas TCP was weakly adsorbed compared to its parent compound. The temporal dissipation patterns of the pesticides and their transformation products will be used as exposure inputs for assessment of their soil microbial toxicity.

Effectiveness of vetiver grass (Vetiveria zizanioides L. Nash) for phytoremediation of endosulfan in two cotton soils from Burkina Faso

The influence of vetiver grass (Vetiveria zizanioides) on the fate of endosulfan was studied using a vertisol and a lixisol soils from cotton-growing areas of Burkina Faso. Endosulfan adsorption isotherms were prepared for planted and unplanted soils. Pot experiments were then conducted for six months. For both soils, endosulfan adsorption was higher on planted soils (K(f) = 6.53-9.73 mg(l-n) L(n) kg(-1)) than on unplanted soils (6.27-7.24 mg(l-n) L(n) kg(-1)). In unplanted soils, vertisol adsorbed more endosulfan than lixisol. From the pot experiments, the estimated half-lives of endosulfan in unplanted soils (40.6 to 43.1 days) were higher than in planted soils (34.5 to 40.6 days) containing a greater number of endosulfan-degrading microorganisms. Six months after treatment, endosulfan was not detected in soils. The effectiveness of vetiver in promoting adsorption and the disappearance of endosulfan in both studied soils should be validated on the cotton plot scale in Burkina Faso.

Fate in the environment and long-range atmospheric transport of the organophosphorus insecticide, chlorpyrifos and its oxon

The fate and movement of the organophosphorus insecticide chlorpyrifos (CPY;CAS No.2921-88-2) and its metabolite chlorpyrifos-oxon (CPYO; CASNo.5598-15-2) determine exposures in terrestrial and aquatic environments.Detectable concentrations of the organophosphorus insecticide CPY in air, rain,snow and other environmental media have been measured in North America and other locations at considerable distances from likely agricultural sources, which indicates the potential for long range transport (LRT) in the atmosphere. This issue was addressed by first compiling monitoring results for CPY in all relevant environmental media. As a contribution to the risk assessment of CPY in remote regions, a simple mass balance model was developed to quantify likely concentrations at locations ranging from local sites of application to more remote locationsup to hundreds of km distant. Physical-chemical properties of CPY were reviewed and a set of consistent values for those properties that determine partitioning and reactivity were compiled and evaluated for use in the model. The model quantifies transformation and deposition processes and includes a tentative treatment of dispersion to lesser atmospheric concentrations. The model also addressed formation and fate of CPYO, which is the major transformation product of CPY. The Characteristic Travel Distance (CTD) at which 63% of the original mass of volatilized CPY is degraded or deposited-based on a conservative concentration of •OHradicals of 0.7 x 106 molecules cm-3 and a half-life of 3 h, was estimated to be 62 km. At lesser concentrations of •OH radical, such as occurs at night and at lesser temperatures, the CTD is proportionally greater. By including monitoring data from a variety of media, including air, rain, snow and biota, all monitored concentrations can be converted to the equilibrium criterion of fugacity, thus providing asynoptic assessment of concentrations of CPY and CPYO in multiple media. The calculated fugacities of CPY in air and other media decrease proportionally with increasing distance from sources, which can provide an approximate prediction of downwind concentrations and fugacities in media and can contribute to improved risk assessments for CPY and especially CPYO at locations remote from points of application, but still subject to LRT. The model yielded estimated concentrations that are generally consistent with concentrations measured, which suggests that the canonical fate and transport processes were included in the simulation model. The equations included in the model enable both masses and concentrations of CPY and CPYO to be estimated as a function of distance downwind following application.While the analysis provided here is useful and an improvement over previous estimates of LRT of CPY and CPYO, there is still need for improved estimates of the chemical-physical properties of CPYO.Based on the persistence in water, soils, and sediments, its bioconcentration and biomagnification in organisms, and its potential for long-range transport, CPY and CPYO do not trigger the criteria for classification as a POP under the Stockholm convention or a PB chemical under EC 1107/2009. Nonetheless, CPY is toxic at concentrations less than the trigger for classification as T under EC 11 07 /2009; however,this simple trigger needs to be placed in the context of low risks to non-target organisms close to the areas of use. Overall, CPY and CPYO are judged to not trigger the PBT criteria of EC 1107/2009.

Biodegradation of organochlorine pesticide endosulfan by bacterial strain Alcaligenes faecalis JBW4

The recently discovered endosulfan-degrading bacterial strain Alcaligenesfaecalis JBW4 was isolated from activated sludge. This strain is able to use endosulfan as a carbon and energy source. The optimal conditions for the growth of strain JBW4 and for biodegradation by this strain were identified, and the metabolic products of endosulfan degradation were studied in detail. The maximum level of endosulfan biodegradation by strain JBW4 was obtained using broth at an initial pH of 7.0, an incubation temperature of 40 degreeC and an endosulfan concentration of 100 mg/L. The concentration of endosulfan was determined by gas chromatography. Strain JBW4 was able to degrade 87.5% of alpha-endosulfan and 83.9% of beta-endosulfan within 5 days. These degradation rates are much higher than the previously reported bacterial strains. Endosulfan diol and endosulfan lactone were the major metabolites detected by gas chromatography-mass spectrometry; endosulfan sulfate, which is a persistent and toxic metabolite, was not detected. These results suggested that A. faecalis JBW4 degrades endosulfan via a non-oxidative pathway. The biodegradation of endosulfan by A. faecalis is reported for the first time. Additionally, the present study indicates that strain JBW4 may have potential for the biodegradation of endosulfan residues.

The effects of endosulfan on cytochrome P450 enzymes and glutathione S-transferases in zebrafish (Danio rerio) livers

Endosulfan, an organochlorine pesticide, has been used worldwide in the past decades. The present study was performed to investigate the effect of endosulfan on liver microsomal cytochrome P450 (CYP) enzymes and glutathione S-transferases (GST) in zebrafish. Male and female zebrafish were separated and exposed to a control and four concentrations of endosulfan (0.01, 0.1, 1, and 10μgL(-1)) and were sampled on days 7, 14, 21, and 28. After exposure to endosulfan, the content of CYP increased and later gradually fell back to control level in most sampling time intervals. A similar tendency was also found in the activities of NADPH-P450 reductase (NCR), aminopyrine N-demethylase (APND) and erythromycin N-demethylase (ERND). GST activities were generally higher in treatment groups than control groups. Regarding sex-based differences, the induction degree of the activity of NCR was generally higher in males than females. Similar differences were also found on the 28th day in the activities of APND and ERND, as well as GST activity on the 7th day. Overall, the present results demonstrate the toxicity at low doses of endosulfan and indicated marked induction of CYP and GST enzymes in zebrafish liver.

Current-use pesticide transport to Costa Rica's high-altitude tropical cloud forest

To gain insight into the atmospheric transport and deposition of organic contaminants in high-altitude forests in the humid tropics, pesticides were analyzed in air, water, and soil samples from Costa Rica. Passive samplers deployed across the country revealed annually averaged air concentrations of chlorothalonil, endosulfan, and pendimethalin that were higher in areas with intensive agricultural activities than in more remote areas. Atmospheric concentrations were particularly high in the intensively cultivated central valley. Only endosulfan and its degradation products were found in soils sampled along an altitudinal transect on the northern side of Volcano Turrialba, which is facing heavily cultivated coastal plains. Consistent with calculations of cold trapping in tropical mountains, concentrations of endosulfan sulfate increased with altitude. Pesticide levels in lake, creek, fog, and arboreal water samples from high-elevation cloud forests were generally below 10 ng · L(-1). Endosulfan sulfate was the most abundant pesticide in water, with concentrations ranging from 0.4 to 9.4 ng · L(-1). Its levels were highest in water sampled from bromeliads. Levels of total endosulfan in water are much lower than the reported median lethal concentration (LC50) value for acute toxicity of α-endosulfan to tadpoles. Although this suggests that the presence of pesticide might not have a direct impact on amphibian populations, the possibility of effects of chronic exposure to a mixture of substances cannot be excluded. Fog was relatively enriched in some of the analyzed pesticides, such as dacthal and chlorothalonil, and may constitute an important deposition pathway to high-altitude tropical cloud forest.

Impact of climatic and soil conditions on environmental fate of atrazine used under plantation forestry in Australia

We studied the leaching and dissipation of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1, 3, 5-s-triazine) and its two principal metabolites (desethylatrazine and desisopropylatrazine) for more than two years through soil profiles at five forestry sites across Australia (representing subtropical, temperate and Mediterranean climatic conditions with rainfall ranging from 780 to 1536 mm yr(-1)). Following atrazine applications at local label rates, soil cores were collected at regular intervals (up to depths of 90-150 cm), and the residues of the three compounds in soil were analysed in composite samples using liquid chromatography. Bromide was applied simultaneously with atrazine to follow the movement of the soil water. While bromide ion rapidly leached through the entire profile, in most cases the bulk of atrazine, desethylatrazine and desisopropylatrazine remained in the top 45 cm of the soil profile. However, a small fraction of residue moved deeper into the soil profile and at a subtropical site (Toolara) trace levels (ng L(-1)) of atrazine and one of its metabolites (DEA) were detected in perched groundwater located at a depth of 1.8 m. Data on the total residues of atrazine in soil profiles from all sites except the Tasmanian site fitted a first-order decay model. The half-life of atrazine in surface soils at the subtropical sites (Toolara and Imbil) ranged from 11 to 21 days. Four separate applications of atrazine at Toolara resulted in a narrow range of half-lives (16 ± 3.6 days), confirming relatively rapid dissipation of atrazine under subtropical conditions (Queensland). In contrast, a prominent biphasic pattern of initial rapid loss followed by very slow phase of degradation of atrazine was observed under the colder temperate climate of Highclere (Tasmania). The data showed that while its 50% (DT(50)) loss occurred relatively rapidly (36 days), more than 10% of herbicide residue was still detectable in the profile even a year after application (DT(90) = 375 days). The rate of dissipation of atrazine at warm subtropical Queensland sites (Imbil and Toolara) was 2-3 times faster than sites located in colder climate of Tasmania. The marked contrast in DT(50) values between subtropical and temperate sites suggest that climatic conditions (soil temperature) is one of the key factors affecting atrazine dissipation. At the Tasmanian site, the combination of leaching of the herbicide in subsoil and slower microbial activity at cooler temperatures would have caused a longer persistence of atrazine.

Fate of pesticides in the arid subtropics, Botswana, Southern Africa

Despite a history of pesticide usage, few data exist on their concentrations in air and soil of Southern Africa. To add to the understanding of the processes controlling the fate of organic contaminants in arid regions, the levels, spatial trends, and seasonal variability of pesticides were studied in air and soil from Botswana. XAD resin-based passive air samplers (PAS) were deployed at 15 sites across the country from May 2006 to May 2007. Soil samples were collected from the vicinity of nine of the PAS sampling sites. In addition, 27 24-h high-volume air samples were collected in Maun, at the southeastern edge of the Okavango Delta, every two weeks for one year. Levels of pesticides in PAS were low, with α-endosulfan and lindane being most abundant. Concentrations in soils were extremely low and only soils with high organic carbon contained notable amounts of dieldrin and traces of other pesticides. In particular, air and soil from the Okavango Delta had very low levels even though the area had repeatedly been sprayed with DDT and endosulfan in the past. Air samples from Eastern Botswana, where the majority of the population lives, contained higher levels. Higher air concentrations of α-endosulfan occurred during summer and higher HCB levels occurred in winter. This seasonality was related with neither minor seasonal changes in temperature nor hydrological seasonal events such as the rainy season or the flooding of the Okavango Delta. Thus, the observed spatial and seasonal patterns are more likely related to pesticide usage pattern than to environmental factors or historical use. High temperature and low organic matter content limit the uptake capacity of most subtropical soils for pesticides. No evidence was found that sorption to dry mineral matter plays a major role. Arid soils in subtropical regions are therefore neither a major reservoir of organic contaminants nor do they constitute a significant long-term source of pesticides to the atmosphere.

Endosulfan, a global pesticide: a review of its fate in the environment and occurrence in the Arctic

This review investigates the fate and behaviour of endosulfan, a current-use organochlorine pesticide, in temperate environments and the Arctic. Usage data and patterns, physical-chemical properties, environmental partitioning and degradation, environmental levels, global distribution and temporal trends are evaluated and discussed in the context of criteria that designate a substance as a persistent organic pollutant. Endosulfan is one of the most abundant OC pesticides in the global atmosphere and is capable of undergoing long range transport to remote locations such as the Arctic. Degradation of the two isomers, alpha- and beta-endosulfan, does occur in temperate/tropical soil and aquatic systems, both by abiotic and biotic processes, although this is highly dependent on the prevailing environmental conditions. Endosulfan sulfate is the major metabolite and this recalcitrant compound has been detected in air and is present in remote mountain lake sediments, although in comparison to alpha-endosulfan, data for this compound in the wider environment are lacking. Temporal trends from ice/snow cores as well as mountain lake sediments reveal a marked increase in endosulfan accumulation from the 1980s onwards. Furthermore, unlike other 'legacy' OC pesticides, levels of alpha-endosulfan do not show a decline in atmospheric monitoring data, reflecting ongoing use of this pesticide in the northern hemisphere. Endosulfan is present at low concentrations (relative to the pesticide, lindane) in surface Arctic Ocean waters, with the atmosphere likely to be the major contemporary source. Residues of endosulfan have been detected in marine biota for different geographical regions of the Arctic, with higher bioaccumulation factors (>10(3)-10(7)) for zooplankton and various species of fish, compared to studies in warmer/temperate systems. Endosulfan is present in marine mammals, although there is uncertainty in the various Arctic biota datasets due to differences in analytical techniques. For some biota, biomagnification factors for alpha-endosulfan are >1, notably from fish to seal, although there is a wide variability in values between the same species for different regions of the Arctic. There is little if any evidence of trophic magnification of alpha-endosulfan in well-defined marine foodwebs, with some evidence of bio-dilution at higher trophic levels, presumably due to increased metabolism. Endosulfan does fulfil several of the criteria under the UNEP Stockholm Convention for designation as a persistent organic pollutant. The alpha- and beta-isomer have similar physical-chemical properties and environmental behaviour to some of the obsolete organochlorine pesticides, although an assessment of their persistence and toxicity should be viewed alongside endosulfan sulfate, as 'Sigmaendosulfan'. Persistence of 'Sigmaendosulfan' coupled to ongoing use of endosulfan pesticides, will ensure continued long-range transport and contamination of remote environments.

Implications of differences between temperate and tropical freshwater ecosystems for the ecological risk assessment of pesticides

Despite considerable increased pesticide use over the past decades, little research has been done into their fate and effects in surface waters in tropical regions. In the present review, possible differences in response between temperate and tropical freshwaters to pesticide stress are discussed. Three underlying mechanisms for these differences are distinguished: (1) climate related parameters, (2) ecosystem sensitivity, and (3) agricultural practices. Pesticide dissipation rates and vulnerability of freshwaters appear not to be consistently higher or lower in tropical regions compared to their temperate counterparts. However, differences in fate and effects may occur for individual pesticides and taxa. Furthermore, intensive agricultural practices in tropical countries lead to a higher input of pesticides and spread of contamination over watersheds. Field studies in tropical farms on pesticide fate in the enclosed and surrounding waterways are recommended, which should ultimately lead to the development of surface water scenarios for tropical countries like developed by the Forum for the co-ordination of pesticide fate models and their use for temperate regions. Future tropical effect assessment studies should evaluate whether specific tropical taxa, not represented by the current standard test species in use, are at risk. If so, tropical model ecosystem studies evaluating pesticide concentration ranges need to be conducted to validate whether selected surrogate indigenous test species are representative for local tropical freshwater ecosystems.

Endosulfan application to a stream mesocosm: studies on fate, uptake into passive samplers and caged toxicity test with the fish M. ambigua

A model mesocosm system was used to simulate the effect of endosulfan entering a waterway from episodic events such as accidental overspray or in runoff water containing contaminated sediment following storm events. The fate of technical endosulfan applied to a 24-stream mesocosm was compared in experiments where the pesticide was applied either directly as water contamination or after being pre-bound to sediment. The flow of water through the streams was discontinued for a 10-12 h period following the pesticide application. Following the water application, only approximately 3% of endosulfan remained in the streams after 4 days and then was not detectable after 7 days. In contrast, after application pre-bound to sediment, approximately 33% of the endosulfan remained in the streams after 4 days and 14% after 7 days. Additionally, with the sediment-bound application, the proportion of endosulfan was higher in the substrate (11%) after 7 days than in the overlying water (3%), and approximately 1% was oxidised to the sulphate form. The dissipation of endosulfan in the water column of both experiments followed a two-parameter exponential decay model characterised by a relatively fast first-order single-phase process. In sediment of both experiments and the gravel of the sediment-dosing experiment, the dissipation of endosulfan followed more closely a four-parameter bi-exponential decay model characterised by first-order kinetics of two fractions: the first fraction dissipates quickly, and in the longer term the second fraction dominates the overall dissipation with a slower rate. In the gravel section of the water-dosing experiment, endosulfan dissipation was characterised by relatively very slow two-parameter exponential decay. The overall dissipation rates of the alpha- and beta-endosulfan isomers were significantly higher in the water-dosing than in the sediment-dosing experiment, except in the gravel section of the mesocosm. The uptake of the endosulfan into passive samplers constructed from polyethylene membrane bags containing trimethylpentane solvent (TRIMPS) placed in the overlying water was linear. In contrast, TRIMPS buried in sediment failed to uptake endosulfan from the sediment substrate, indicating that short-term deployment of passive samplers can only be used to determine time-weighted average concentrations of bioavailable chemicals in the water column. A 34-h LC50 of 2.8 microg/l [95% confidence interval (CI) 1.5-4.2 microg/l] for juveniles of the native fish Macquaria ambigua was obtained when exposed during the water-dosing experiment. This study demonstrated that the pulse entry of sediment contaminated with endosulfan into a receiving waterway was more persistent compared with direct aqueous contamination and the endosulfan would be bioavailable to pelagic organisms following a gradual partitioning to the water column.

Impact of repeated pesticide applications on the binding and release of methyl 14C-monocrotophos and U-ring labelled 14C-carbaryl to soil matrices under field conditions

The dissipation of (O-methyl-14C) monocrotophos and U-ring labelled 14C-carbaryl was monitored for over two years in absence and presence of other insecticides using in situ soil columns. The dissipation of 14C-monocrotophos from soil treated with methomyl and carbaryl showed a faster rate of downward movement than in a control column tagged with the labelled insecticide alone. The same trend was observed in experiments with 14C-carbaryl that dissipated more readily in soil treated with non-labelled monocrotophos and methomyl. In the presence of other insecticides the percentage of bound residues was generally lower than in control experiments. The bound residues at the top of the column are released at a low rate under conditions prevailing in the field. The overall time required for dissipation of 50% of monocrotophos and carbaryl (t50) as estimated from control experiment was approximately 20 and 24 weeks, respectively. The data indicate that repeated applications of pesticides might enhance the release of 14C-bound residues.

Formation of pesticide nonextractable (bound) residues in soil: magnitude, controlling factors and reversibility

The analysis of the coherent data on nonextractable (bound) residues (NER) from the literature and EU pesticide registration dossiers allows the identification of general trends, in spite of the large variability and heterogeneity of data. About 50% of the pesticides reviewed exhibit a low proportion of NER (less than 30% of the initial amount) while only 12% of pesticides have a proportion of NER exceeding 70%. The lowest proportion of NER was found for dinitroanilines (<20%), and the largest value was obtained for carbamates, and in particular dithiocarbamates. The presence of chemical reactive groups, such as aniline or phenol, tends to yield a larger proportion of NER. NER originating from N-heteroatomic ring were found to be lower than those from phenyl-ring structures. Among the environmental factors affecting the formation of NER, microbial activity has a direct and significant effect. Concerning the NER uptake or their bioavailability, consistent data suggest that only a small percentage of the total amounts of NER can be released. The analysis of NER formation kinetics showed that incubation experiments are often stopped too early to allow a correct evaluation of the NER maturation phase. Therefore, there is a need for longer term experiments to evaluate the tail of the NER formation kinetics. Still, the heterogeneity of the NER data between pesticides and for specific pesticides calls for great care in the interpretation of the data and their generalization.

Pesticide fate in tropical wetlands of Brazil: an aquatic microcosm study under semi-field conditions

A contamination of off-site aquatic environments with pesticides has been observed in the tropics, yet only sparse information exists about pesticide fate in such ecosystems. The objective of our semi-field study was to elucidate the fate of alachlor, atrazine, chlorpyrifos, endosulfan, metolachlor, profenofos, simazine, and trifluralin in the aqueous environment of the Pantanal wetland (MT, Brazil). To this aim, water and water/sediment microcosms of two sizes (0.78 and 202 l) were installed in the outskirts of this freshwater lagoon environment and pesticide dissipation was monitored for up to 50 d after application. The physical-chemical water conditions that developed in the microcosms were reproducible among field replicates for both system sizes. Pesticide dissipation was substantially enhanced for most pesticides in small microcosms relative to the large ones (reduced DT(50) by a factor of up to 5.3). The presence of sediment in microcosms led to increased persistence of chlorpyrifos, endosulfan, and trifluralin in the test systems, while for polar pesticides (alachlor, atrazine, metolachlor, profenofos, and simazine) a lesser persistence was observed. Atrazine, simazine, metolachlor, and alachlor were identified as the most persistent pesticides in large water microcosms (DT(50) > or = 47 d); in large water/sediment systems endosulfan beta, atrazine, metolachlor, and simazine showed the slowest dissipation (DT(50) > or = 44 d). A medium-term accumulation in the sediment of tropical ecosystems can be expected for chlorpyrifos and endosulfan isomers (11-35% of applied amount still extractable at 50 d after application). We conclude that the persistence of the studied pesticides in aquatic ecosystems of the tropics is not substantially lower than during summer in temperate regions.

Chemistry and fate of simazine

Simazine, first introduced in 1956, is a popular agricultural herbicide used to inhibit photosynthesis in broadleaf weeds and grasses. It is a member of the triazine family, and according to its physicochemical properties, it is slightly soluble in water, relatively nonvolatile, capable of partitioning into organic phases, and susceptible to photolysis. Sorption and desorption studies on its behavior in soils indicate that simazine does not appreciably sorb to minerals and has the potential to leach in clay and sandy soils. The presence of organic matter in soils contributes to simazine retention but delays its degradation. The primary sorptive mechanism of simazine to OM has been proposed to be via partitioning and/or by the interaction with functional groups of the sorbent. Farming practices directly influence the movement of simazine in soils as well. Tilled fields lower the runoff of simazine when compared to untilled fields, but tilling can also contribute to its movement into groundwater. Planting cover crops on untilled land can significantly reduce simazine runoff. Such practices are important because simazine and its byproducts have been detected in groundwater in The Netherlands, Denmark, and parts of the U.S. (California, North Carolina, Illinois, and Wisconsin) at significant concentrations. Concentrations have also been detected in surface waters around the U.S. and United Kingdom. Although the physicochemical properties of simazine do not support volatilization, residues have been found in the atmosphere and correlate with its application. Although at low concentrations, simazine has also been detected in precipitation in Pennsylvania (U.S.), Greece, and Paris (France). Abiotically, simazine can be oxidized to several degradation products. Although hydrolysis does not contribute to the dissipation of simazine, photolysis does. Microbial degradation is the primary means of simazine dissipation, but the process is relatively slow and kinetically controlled. Some bacteria and fungal species capable of utilizing simazine as a sole carbon and nitrogen source at a fast rate under laboratory conditions have been identified. Metabolism of simazine in higher organisms is via cytochrome P-450-mediated oxidation and glutathione conjugation.

Influence of soil aging on sorption and bioavailability of simazine

Characterization of pesticide bioavailability, particularly in aged soils, is of continued interest because this information is necessary for environmental risk assessment. However, pesticide bioavailability in aged soils has been characterized by a variety of methods with limited success, due in part to methodological limitations. The objective of this study was to use solvent extraction methods to correlate simazine residue bioavailability in aged soils to simazine mineralization using a simazine-mineralizing bacterium. Soils from Brazil, Hawaii, and the midwestern United States were treated with UL-ring-labeled [14C]simazine and incubated for up to 8 weeks. At the end of each incubation period, soils were either incubated further, extracted with 0.01 M CaCl2, or extracted with aqueous methanol (80:20 v/v methanol/water). In a parallel experiment, after each incubation period, soils were inoculated with the bacterium Pseudomonas sp. strain ADP, which is capable of rapidly mineralizing simazine, and 14CO2 was determined. The inoculated soil samples were then extracted with 0.01 N CaCl2 and with aqueous methanol. This allowed for the evaluation of the bioavailability of aged simazine residues, without the contribution of simazine desorption from soil. Results of these studies indicated that simazine sorption to soil increased with aging and that amounts of simazine in aged soils extracted by 0.01 M CaCl2 and aqueous methanol were highly correlated to amounts of simazine mineralized by Pseudomonas sp. strain ADP. Consequently, 0.01 M CaCl2/methanol-extractable simazine in aged soils can be used to estimate bioavailable residues. This technique may be useful in determining the bioavailability of other s-triazine compounds in soils.

Environmental fate of herbicides trifluralin, metazachlor, metamitron and sulcotrione compared with that of glyphosate, a substitute broad spectrum herbicide for different glyphosate-resistant crops

The introduction of crops resistant to the broad spectrum herbicide glyphosate, N-(phosphonomethyl)glycine, may constitute an answer to increased contamination of the environment by herbicides, since it should reduce the total amount of herbicide needed and the number of active ingredients. However, there are few published data comparing the fate of glyphosate in the environment, particularly in soil, with that of substitute herbicides. The objective of this study is to compare the fate of glyphosate in three soils with that of four herbicides frequently used on crops that might be glyphosate resistant: trifluralin, alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine, and metazachlor, 2-chloro-N-(pyrazol-1-ylmethyl)acet-2',6'-xylidide for oilseed rape, metamitron, 4-amino-4,5-dihydro-3-methyl-6-phenyl-1,2,4-triazin-5-one for sugarbeet and sulcotrione, 2-(2-chloro-4-mesylbenzoyl)cyclohexane-1,3-dione for maize. The distribution of herbicides between the volatilized, mineralized, extractable and non-extractable fractions was studied, along with the formation of their metabolites in laboratory experiments using 14C-labelled herbicides, over a period of 140 days. The main dissipation pathways were mineralization for glyphosate and sulcotrione, volatilization for trifluralin and non-extractable residues formation for metazachlor and metamitron. The five herbicides had low persistence. Glyphosate had the shortest half-life, which varied with soil type, whereas trifluralin had the longest. The half-lives of metazachlor and sulcotrione were comparable, whereas that of metamitron was highly variable. Glyphosate, metazachlor and sulcotrione were degraded into persistent metabolites. Low amounts of trifluralin and metamitron metabolites were observed. At 140 days after herbicide applications, the amounts of glyphosate and its metabolite residues in soils were the lowest in two soils, but not in the third soil, a loamy sand with low pH. The environmental advantage in using glyphosate due to its rapid degradation is counterbalanced by accumulation of aminomethylphosphonic acid specifically in the context of extensive use of glyphosate.

Volatilization of alachlor from polymeric formulations

Pesticides may be dispersed throughout the environment by several means, including groundwater contamination, surface water contamination, and volatilization with subsequent atmospheric transport and deposition. In earlier research primarily directed at reducing the potential for groundwater contamination, a number of herbicides were microencapsulated within several different polymers. These polymeric formulations were evaluated for efficacy in the greenhouse. In the studies described in this paper, three polymeric alachlor formulations that were the most effective in the greenhouse were evaluated in laboratory volatility studies using pure alachlor and a commercial formulation (Lasso 4EC) for comparison purposes. In a given experiment, technical alachlor, Lasso 4EC, and two polymeric formulations were applied to soil and evaluated in a contained system under 53% humidity with a fixed flow rate. Evolved alachlor was collected in ethylene glycol, recovered with C18 solid phase extraction cartridges, and analyzed by reverse-phase high-performance thin-layer chromatography with densitometry. Duration of the studies ranged from 32 to 39 days. In studies in which all formulations were uniformly incorporated in the soil, total alachlor volatilization from the polymeric microcapsules was consistently lower than that from the alachlor and Lasso 4EC formulations. In studies in which the polymeric formulations were sprinkled on the surface of the soil, microcapsules prepared with the polymer cellulose acetate butyrate released the smallest quantity of volatilized alachlor.