Pesticide exposure assessment in rice paddies in Europe: a comparative study of existing mathematical models

A comparative test was undertaken in order to identify the potential of existing mathematical models, including the rice water quality (RICEWQ) 1.6.4v model, the pesticide concentration in paddy field (PCPF-1) model and the surface water and groundwater (SWAGW) model, for calculating pesticide dissipation and exposure in rice paddies in Europe. Previous versions of RICEWQ and PCPF-1 models had been validated under European and Japanese conditions respectively, unlike the SWAGW model which was only recently developed as a tier-2 modelling tool. Two datasets, derived from field dissipation studies undertaken in northern Italy with the herbicides cinosulfuron and pretilachlor, were used for the modelling exercise. All models were parameterized according to field experimentations, as far as possible, considering their individual deficiencies. Models were not calibrated against field data in order to remove bias in the comparison of the results. RICEWQ 1.6.4v provided the highest agreement between measured and predicted pesticide concentrations in both paddy water and paddy soil, with modelling efficiency (EF) values ranging from 0.78 to 0.93. PCPF-1 simulated well the dissipation of herbicides in paddy water, but significantly underestimated the concentrations of pretilachlor, a chemical with high affinity for soil sorption, in paddy soil. SWAGW simulated relatively well the dissipation of both herbicides in paddy water, and especially pretilachlor, but failed to predict closely the pesticide dissipation in paddy soil. Both RICEWQ and SWAGW provided low groundwater (GW) predicted environmental concentrations (PECs), suggesting a low risk of GW contamination for the two herbicides. Overall, this modelling exercise suggested that RICEWQ 1.6.4v is currently the most reliable model for higher-tier exposure assessment in rice paddies in Europe. PCPF-1 and SWAGW showed promising results, but further adjustments are required before these models can be considered as strong candidates for inclusion in the higher-tier pesticide regulatory scheme.     

苯噻草胺在稻田水及土壤中的消解动态

研究建立了稻田水和土壤中苯噻草胺残留的检测方法。稻田水经过滤后直接进高效液相色谱-串联质谱(HPLC-MS/MS)仪分析,方法的线性范围为0.1~10 μ g/L,相关系数(R2)为0.999 3,检出限(LOD)为0.03 μ g/L,定量限(LOQ)为0.1 μ g/L;当样品中苯噻草胺的添加水平为0.1~10 μ g/L时,平均回收率在98.4%~103.2%之间,相对标准偏差(RSD)在1.9%~3.4%之间。土壤经乙腈提取,硅胶固相萃取柱净化后用高效液相色谱(带二极管阵列检测器,HPLC-DAD)仪检测,方法的线性范围为0.1 ~2 mg/L,R2为0.998 5,LOD为0.006 mg/kg,LOQ为0.02 mg/kg;当样品中苯噻草胺的添加水平为0.02~1 mg/kg时,平均回收率在75.2%~86.1%之间,RSD在3.3%~7.5%之间。采用所建立方法对北京、南京两地2009年苯噻草胺在稻田水及土壤中的消解动态进行了检测。结果表明:其在稻田水及土壤中的消解动态曲线符合一级动力学方程;苯噻草胺在稻田水中消解迅速,半衰期分别为2.1 d(北京)和1.6 d(南京);其在土壤中的消解速率两地间差异较大,且比水中的慢,半衰期分别为12.3 d(北京)和3.7 d(南京)。     

Test of the Root Zone Water Quality Model (RZWQM) for predicting runoff of atrazine, alachlor and fenamiphos species from conventional-tillage corn mesoplots

The Root Zone Water Quality Model (RZWQM) is a comprehensive, integrated physical, biological and chemical process model that simulates plant growth and movement of water, nutrients and pesticides in a representative area of an agricultural system. We tested the ability of RZWQM to predict surface runoff losses of atrazine, alachlor, fenamiphos and two fenamiphos oxidative degradates against results from a 2-year mesoplot rainfall simulation experiment. Model inputs included site-specific soil properties and weather, but default values were used for most other parameters, including pesticide properties. No attempts were made to calibrate the model except for soil crust/seal hydraulic conductivity and an adjustment of pesticide persistence in near-surface soil. Approximately 2.5 (+/- 0.9), 3.0 (+/- 0.8) and 0.3 (+/- 0.2)% of the applied alachlor, atrazine and fenamiphos were lost in surface water runoff, respectively. Runoff losses in the 'critical' events--those occurring 24 h after pesticide application--were respectively 91 (+/- 5), 86 (+/- 6) and 96 (+/- 3)% of total runoff losses for these pesticides. RZWQM adequately predicted runoff water volumes, giving a predicted/observed ratio of 1.2 (+/- 0.5) for all events. Predicted pesticide concentrations and loads from the 'critical' events were generally within a factor of 2, but atrazine losses from these events were underestimated, which was probably a formulation effect, and fenamiphos losses were overestimated due to rapid oxidation. The ratios of predicted to measured pesticide concentrations in all runoff events varied between 0.2 and 147, with an average of 7. Large over-predictions of pesticide runoff occurred in runoff events later in the season when both loads and concentrations were small. The normalized root mean square error for pesticide runoff concentration predictions varied between 42 and 122%, with an average of 84%. Pesticide runoff loads were predicted with a similar accuracy. These results indicate that the soil-water mixing model used in RZWQM is a robust predictor of pesticide entrainment and runoff.     

Herbicide movement in soils: principles, pathways and processes

European legislation concerning ground- and surface-water quality and the protection of non-target organisms in surface-water from pesticide contamination has initiated more stringent data requirements from regulatory authorities concerning the movement of all pesticides in soils. Other interested parties, such as water companies, environment agencies and consumer-driven organizations, have sought to influence the use of herbicides and their impact on the environment. The resulting studies and associated research have led to a better understanding of the fate and behaviour of herbicides in the soil environment. The amount of herbicide that moves away from the area of application will depend on the physico-chemical properties of the chemical and the agroclimatic characteristics of the target site. Under average conditions, the amount of herbicide lost by movement from a soil profile is typically <0.1% to 1% of the applied mass but, under certain localized circumstances, can reach up to 5% or greater. Leaching, drain-flow and surface run-off are the main pathways responsible for herbicide movement within soils. The soil/herbicide processes determining the losses are also variable in both time and space. It is therefore necessary to understand the spatial characteristics of soils, their hydrology and the associated herbicide use patterns.     

五氟磺草胺在稻田中的消解动态及残留特性

建立了超高效液相色谱-质谱联用检测五氟磺草胺在水稻植株、稻田土壤、田水和糙米中残留的分析方法,结合田间试验研究了五氟磺草胺在稻田环境中的消解及残留特性,并对稻米中五氟磺草胺残留的膳食暴露进行了初步评估。结果表明:在0.005~0.5 mg/L范围内,五氟磺草胺的质量浓度与对应的峰面积间呈良好线性关系,检出限（LOD）为0.001~0.002 mg/kg,定量限（LOQ）为0.003~0.005 mg/kg。在0.005~0.5 mg/kg添加水平下,五氟磺草胺在水稻植株、稻田土壤、田水和糙米中的平均回收率在89%~106%之间,相对标准偏差在2.8%~8.5%之间。浙江、福建和黑龙江2年3地的田间试验表明:0.025%五氟磺草胺颗粒剂在水稻植株、稻田土壤和田水中的消解半衰期分别为1.5~3.3,3.0~4.7和1.6-3.0 d,说明该药剂在稻田环境中消解速率较快。以五氟磺草胺有效成分含量37.5和56.3 g/hm2分别施药1次,于水稻成熟期采样检测,发现其在糙米中的残留量低于0.005 mg/kg,表明其膳食摄入风险很低,该研究结果可为五氟磺草胺风险评估提供一定参考。     

高效液相色谱-串联质谱法检测稻田中吡嘧磺隆和苯噻酰草胺残留

采用高效液相色谱-串联质谱法(HPLC-MS/MS),建立了稻田水、土壤、水稻植株、稻秆、稻壳及糙米基质中吡嘧磺隆和苯噻酰草胺的残留分析方法。样品经20 m L V(乙腈)∶V(水)=70∶30的混合溶液提取,提取液用20 mg石墨化碳黑(GCB)与30 mg乙二氨基-N-丙基硅烷(PSA)净化,HPLC-M S/M S检测。吡嘧磺隆在上述各基质中的添加回收率在76%~107%之间,相对标准偏差(RSD)在1.5%~14%之间,定量限为0.004~0.01 mg/kg;苯噻酰草胺的添加回收率在77%~101%之间,RSD在2.4%~13%之间,定量限为0.001~0.01 mg/kg。实现了对两种除草剂同时简便、快速测定的要求。采用该方法测定了26%吡嘧磺隆·苯噻酰草胺水面扩展粒剂在稻田施用后,其有效成分吡嘧磺隆和苯噻酰草胺在实际样品中的残留量。结果表明,两种除草剂均属于易降解农药,在本试验条件下其在糙米中的残留量均低于我国最大残留限量(MRL)(吡嘧磺隆0.1 mg/kg;苯噻酰草胺0.05 mg/kg)。     

Fate of carbofuran in model rice/fish ecosystems

The distribution and fate of [¹⁴C]carbofuran were studied in model earlyseason rice/fish and late-season rice/fish ecosystems after its application by respectively soil incorporation and broadcasting. The differences observed in the behaviour of the insecticide in these two rice/fish ecosystems indicated the important effect of the different application methods on the fate of the chemical in the environment. The radioactive residues in the paddy water, rice plants and fish were much lower when the pesticide was incorporated into the soil surface layer. An obvious vertical movement of carbofuran residues occurred in the paddy soil profile. Bound residues constituted the majority of the residues in the paddy soil, rice plants and fish tissues. 3-Hydroxy- and 3-ketocarbofuran and carbofuran phenol were tentatively identified as the main degradation products in the paddy water, paddy soil, rice plants and fish.     

SWAT—A Semi-empirical Model to Predict Concentrations of Pesticides Entering Surface Waters from Agricultural Land

A semi-empirical model called SWAT has been developed to predict concentrations of agriculturally applied pesticides moving to surface waters, an aspect which is not well described by current models for pesticide fate. The model is based upon a direct hydrological link established between soil type and the amount of water moving rapidly to streams in response to rainfall. Attenuation factors describe the decrease in concentrations of pesticide between field application and loss in water moving from the site into surface waters. Evaluation of model predictions against available field data from three sites and four soil types in England shows that SWAT is capable of predicting the transient peak concentrations of a wide range of pesticides during rapid water movement to streams in response to rainfall. Predicted concentrations were too great when rainfall initiated water movement to streams very soon after pesticide application, particularly for the more mobile pesticides, and some predictions for pesticides sorbed very strongly to soil were relatively poor. Almost all of the predicted concentrations were within one order of magnitude of measured values.     

Exposure risk assessment and evaluation of the best management practice for controlling pesticide runoff from paddy fields. Part 1: Paddy watershed monitoring

Rice pesticide concentrations in surface water along with hydrological balance and water management conditions were investigated in a paddy watershed of about 100 ha at the Sakura river basin in Tsukuba, Japan, for 3 years from April 2002. Monitoring on different hydrological scales ranging from a paddy plot up to a watershed determined the importance of water management associated with rainfall events and the cyclic irrigation for reducing pesticide discharge into aquatic environments. Surface drainage significantly increased as a response to rainfall events greater than about 1.5 cm day(-1). A total of 16 herbicides were detected in the stream water and their peak concentrations mostly occurred from early to mid-May following the pesticide application period. Two water management factors influencing the pesticide runoff from paddy fields were defined: excess water storage capacity (EWSC) and water holding period (WHP). Uncertainty analyses of pesticide discharge from a paddy plot for dymron (daimuron) and imazosulfuron (IMS) were performed using Monte Carlo simulation (MCS) with prescribed probability of rainfall and water management practice from observations over a period of 3 years. Application of an intermittent irrigation scheme with shallow water depth practice and high drainage gate to maintain the EWSC > 2 cm and increasing WHP from the current Japanese Agricultural Chemicals Regulation law of 3-4 days to at least 10 days were recommended for reducing the pesticide runoff from paddy fields in a monsoon region such as in Japan. The combination of good water management in field plots and small-scale water cycling is the best management practice for controlling pesticide discharge from paddy watersheds.     

Pesticide paddy field model (PADDY) for predicting pesticide concentrations in water and soil in paddy fields

To evaluate the fate of pesticides in paddy fields, the pesticide paddy field model (PADDY) has been developed for predicting pesticide concentrations in paddy fields and the run-off amount of pesticides to the aquatic environment. This model focused particularly on granule formulation because these formulations have been used widely as herbicides on paddy fields in Japan. The behavior of pesticides in paddy fields was assessed by considering the main processes on the basis of a compartment system and the mass-balance equations of pesticides in the compartments were derived from kinetic data. The mathematical model, PADDY, was constructed by numerical solution techniques. A method for measuring the pesticide parameters for this model was also developed. To validate the model, a field experiment was carried out on a paddy field and the concentration changes of pesticides in water and soil were measured. These were in reasonably good agreement with those predicted by PADDY. © 1999 Society of Chemical Industry     

呋虫胺及其代谢物在水稻生态系统中的残留检测与消解动态

为评价呋虫胺在水稻生态系统中的残留与消解行为,分别在海南、湖南和黑龙江省3地进行了规范残留试验。建立了超高效液相色谱-串联质谱 (UPLC-MS/MS) 检测呋虫胺 (DNF) 及其代谢物1-甲基-3-[(3-四氢呋喃) 甲基]脲 (UF) 与1-甲基-3-[(3-四氢呋喃) 甲基]二氢胍盐 (DN) 在水稻稻株、土壤、田水、糙米和稻壳中残留的分析方法。样品经含体积分数为1%的乙酸水溶液或乙腈溶液提取,QuEChERS方法净化,以甲醇-水混合溶液为流动相梯度洗脱,多反应监测 (MRM) 模式扫描,外标法定量。结果表明:3种分析物的进样浓度与其峰面积之间呈良好线性相关,R2>0.999。DNF、UF和DN在稻株、土壤、田水、糙米和稻壳中的平均回收率在71%~102%之间,在稻株、土壤、田水和糙米中的相对标准偏差 (RSD) 在1.2%~8.3%之间,在稻壳中的RSD在4.4%~20%之间。3种分析物在稻株、土壤、田水、糙米和稻壳中的最低检测浓度 (LOQ) 分别为0.1 mg/kg、0.02 mg/kg、0.01 mg/L、0.02 mg/kg和0.1 mg/kg。DNF、UF和DN的最小检出量分别为1、0.4和4 pg。3种分析物的消解半衰期分别为:DNF在稻株上为0.41~2.7 d,土壤中为1.6~4.2 d,田水中为0.90~2.2 d;DN在稻株上为2.9~13 d,土壤中为64~65 d,田水中为4.2 d;UF在稻株上为0.43~3.1 d。20%呋虫胺悬浮剂以有效成分120~180 g/hm2的剂量于水稻抽穗期施用2~3次,施药间隔期21 d,分别于距末次施药后14 d与21 d采收,呋虫胺在糙米中的残留最大值为0.11 mg/kg,低于中国制定的其在糙米上的最大残留限量标准1 mg/kg。     

Identification of key climatic factors regulating the transport of pesticides in leaching and to tile drains

BACKGROUND: Key climatic factors influencing the transport of pesticides to drains and to depth were identified. Climatic characteristics such as the timing of rainfall in relation to pesticide application may be more critical than average annual temperature and rainfall. The fate of three pesticides was simulated in nine contrasting soil types for two seasons, five application dates and six synthetic weather data series using the MACRO model, and predicted cumulative pesticide loads were analysed using statistical methods. RESULTS: Classification trees and Pearson correlations indicated that simulated losses in excess of 75th percentile values (0.046 mg m(-2) for leaching, 0.042 mg m(-2) for drainage) generally occurred with large rainfall events following autumn application on clay soils, for both leaching and drainage scenarios. The amount and timing of winter rainfall were important factors, whatever the application period, and these interacted strongly with soil texture and pesticide mobility and persistence. Winter rainfall primarily influenced losses of less mobile and more persistent compounds, while short-term rainfall and temperature controlled leaching of the more mobile pesticides. CONCLUSIONS: Numerous climatic characteristics influenced pesticide loss, including the amount of precipitation as well as the timing of rainfall and extreme events in relation to application date. Information regarding the relative influence of the climatic characteristics evaluated here can support the development of a climatic zonation for European-scale risk assessment for pesticide fate.     

Predicted impact of transgenic, herbicidetolerant corn on drinking water quality in vulnerable watersheds of the mid-western USA

In the intensely farmed corn-growing regions of the mid-western USA, surface waters have often been contaminated by herbicides, principally as a result of rainfall runoff occurring shortly after application of these to corn and other crops. In some vulnerable watersheds, water quality criteria for chronic human exposure through drinking water are occasionally exceeded. We selected three settings representative of vulnerable corn-region watersheds, and used the PRZM-EXAMS model with the Index Reservoir scenario to predict corn herbicide concentrations in the reservoirs as a function of herbicide properties and use pattern, site characteristics and weather in the watersheds. We compared herbicide application scenarios, including broadcast surface pre-plant atrazine and alachlor applications with a glyphosate pre-plant application, scenarios in which losses of herbicides were mitigated by incorporation or banding, and scenarios in which only glyphosate or glufosinate post-emergent herbicides were used with corn genetically modified to be resistant to them. In the absence of drift, in almost all years a single runoff event dominates the input into the reservoir. As a result, annual average pesticide concentrations are highly correlated with annual maximum daily values. The modeled concentrations were generally higher than those derived from monitoring data, even for no-drift model scenarios. Because of their lower post-emergent application rates and greater soil sorptivity, glyphosate and glufosinate loads in runoff were generally one-fifth to one-tenth those of atrazine and alachlor. These model results indicate that the replacement of pre-emergent corn herbicides with the post-emergent herbicides allowed by genetic modification of crops would dramatically reduce herbicide concentrations in vulnerable watersheds. Given the significantly lower chronic mammalian toxicity of these compounds, and their vulnerability to breakdown in the drinking water treatment process, risks to human populations through drinking water would also be reduced.     

Impacts of tillage and application methods on atrazine and alachlor losses from upland fields

The effects of tillage practises and the methods of chemical application on atrazine and alachlor losses through run-off were evaluated for five treatments: conservation (untilled) and surface (US), disk and surface, plow and surface, disk and preplant-incorporated, and plow and preplant-incorporated treatments. A rainfall simulator was used to create 63.5 mm h⁻¹ of rainfall for 60 min and 127 mm h⁻¹ for 15 min. Rainfall simulation occurred 24–36 h after chemical application. There was no significant difference in the run-off volume among the treatments but the untilled treatment significantly reduced erosion loss. The untilled treatments had the highest herbicide concentration and the disk treatments were higher than the plow treatments. The surface treatments showed a higher concentration than the incorporated treatments. The concentration of herbicides in the water decreased with time. Among the experimental sites, the one with sandy loam soil produced the greatest losses, both in terms of the run-off volume and herbicide loss. The US treatments had the highest loss and the herbicide incorporation treatments had smaller losses through run-off as the residue cover was effective in preventing herbicide losses. Incorporation might be a favorable method of herbicide application to reduce the herbicide losses by run-off.     

二氯喹啉草酮在水稻植株上的消解动态及其在稻秆、稻谷和土壤中的最终残留

二氯喹啉草酮是经中国农业农村部批准登记的茎叶处理除草剂,迄今为止对其潜在的环境污染尚未见报道。本研究建立了一种采用QuEChERS前处理方法结合高效液相色谱-串联三重四极杆质谱 (HPLC-MS/MS) 联用技术检测二氯喹啉草酮在水稻植株、稻谷和土壤中残留的方法,并采用该方法测定了二氯喹啉草酮在水稻植株中的消解动态和最终残留。结果表明:二氯喹啉草酮的进样质量浓度与其峰面积间呈良好的线性相关,R2>0.99;其在植株、土壤、田水、稻壳和糙米中的平均回收率在78%~99%之间,相对标准偏差 (RSD) 在3.9%~11%之间,在植株、土壤、田水、稻壳和糙米中的最低检测浓度 (LOQ) 均为0.002 mg/kg。二氯喹啉草酮在水稻植株中的消解半衰期为6.7~12.8 d。以有效成分900~1 350 g/hm2的剂量于水稻苗期施用1次,在施药96 d后采集的土壤、稻壳和糙米中均未检测出二氯喹啉草酮。本研究结果可为水稻中二氯喹啉草酮最大残留限量值和田间使用规范的制定提供参考。     

五氟磺草胺在稻田环境中吸附和消解研究进展

五氟磺草胺作为苗后除草剂被广泛应用于水稻田中杂草的防除,其对水生植物、陆生植物和土壤微生物群落可能存在潜在风险,因此,对五氟磺草胺在水土环境中的转化规律与归趋开展定量研究,已受到学者们的关注。本文对五氟磺草胺在稻田水土环境中的吸附、降解以及对周围环境影响方面的研究进展进行了综述、归纳和分析。指出目前对五氟磺草胺在土壤中吸附的研究报道较少,尚未见有关其在水土环境中运移方面的研究,同时应加强其对水土环境风险评估的研究。     

Degradation of oxadiazon in Kalyani alluvial soil

Residual fate and behaviour of the herbicide oxadiazon in Kalyani soil, paddy straw and grain were studied under subtropical conditions, in West Bengal following application @ 1 kg and 2 kg ha⁻¹. Dissipation of oxadiazon in soil followed first-order kinetics and DT₅₀ values ranged from 44 to 45 days. Residues at harvest in paddy grains and straw were also studied. Degradation of oxadiazon after 60 days of incubation at 28(± 1) °C in alluvial soil at water holding capacity yielded 10 metabolites of which four were characterised by spectroscopy. © 1999 Society of Chemical Industry     

Influence of topsoil tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil

Twelve lysimeters with a surface area of 0.5 m² and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural tilth or a finer topsoil tilth. The influence of topsoil tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h^?1 over a 4‐week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4‐week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer tilth. However, generation of the fine tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains. © 2001 Society of Chemical Industry     

The fate of imazapyr in a Swedish railway embankment

The long-term fate of the herbicide imazapyr [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)nicotinic acid] applied to a Swedish railway embankment was studied. Imazapyr was applied at 750 and 1500 g ha(-1) by a spraying train used for full-scale herbicide treatment operations. Soil and groundwater were sampled twice a year for 8 years after application of the herbicide, and the dissipation of imazapyr was studied by HPLC analysis of the residues in soil and groundwater. A clean-up procedure including solid-phase extraction was performed prior to detection by HPLC. Recoveries of imazapyr from soil and water samples were 76-98% and 61-90%, respectively, and detection levels were 0.003 mg kg(-1) and 0.05 microg litre(-1), respectively. Sorption, desorption and microbial amount and activity were also measured at the two locations. The organic matter content correlated positively and the pH negatively to the adsorption of imazapyr on soil, and increasing organic matter contents decreased desorption. Apart from the 0-10-cm top layers of both sites, the microbial amount and activity were small. The main proportion of imazapyr was found in the upper 30 cm of the soil, and degraded with a half-life in the range 67-144 days. Small amounts were transported to lower soil layers and to the groundwater in proportion to the amounts applied. Traces of imazapyr were detected in the groundwater even 8years after application. It was concluded that environmental risks from the use of herbicides on railway embankments could be reduced by including adsorption layers in the embankment during their construction and by reducing the dose of the herbicide used.     

Simazine dynamics in a vineyard soil at Casablanca valley, Chile

Field dissipation, soil movement and laboratory leaching studies were performed to elucidate the effect of two rainfall amounts in the behaviour and environmental fate of simazine under climatic conditions at Casablanca Valley, Chile. Dissipation and soil movement were studied in a field vineyard with a sandy loam soil (Inceptisol; 74.08% sand; 14.87% silt and 11.04% clay). Simazine was applied to bare soil at 2.0 kg AI ha(-1), and its concentration was measured using immunoassay (ELISA) at 0, 10, 20, 40 and 90 days after application under two rainfall amounts, natural field conditions (39 mm) and modified conditions (39 + 180 mm). Simazine leaching was studied using soil core PVC lysimeters (0.9 m height; 0.22 m diameter). Field dissipation data were adjusted with a bi-exponential model. Half-life (DT(50)) values varied between 31.3 (+/-2.5) and 19.0 (+/-4.2) days under natural and modified conditions, respectively. Simazine K(d) varied from 0.42 to 2.15 (K(oc) 32.6-216.2) in the soil profile. Simazine was detected at a 90-cm soil depth in concentrations of 0.0085 (+/-0.0043) mg kg(-1) and 0.0321 (+/-0.001) mg kg(-1) under field and modified conditions, respectively. The maximum simazine leachate concentrations were 0.013 (+/-0.00084) mg litre(-1) (0.012% of total applied simazine) and 0.0084 (+/-0.00082) mg litre(-1) (0.11% of total applied simazine) for field and modified conditions respectively. These data indicate that water quantity has a significant effect on the DT(50) and the amount of simazine that moved through the soil profile, but not on the soil depth reached by this herbicide.