Effect of water management practice on pesticide behavior in paddy water

The fate and transport of three herbicides commonly used in rice production in Japan were compared using two water management practices. The herbicides were simetryn, thiobencarb and mefenacet. The first management practice was an intermittent irrigation scheme using an automatic irrigation system (AI) with a high drainage gate and the second one was a continuous irrigation and overflow drainage scheme (CI) in experimental paddy fields. Dissipation of the herbicides appeared to follow first order kinetics with the half-lives (DT₅₀) of 1.6-3.4 days and the DT₉₀ (90% dissipation) of 7.4-9.8 days. The AI scheme had little drainage even during large rainfall events thus resulting in losses of less than 4% of each applied herbicide through runoff. Meanwhile the CI scheme resulted in losses of about 37%, 12% and 35% of the applied masses of simetryn, thiobencarb and mefenacet, respectively. The intermittent irrigation scheme using an automatic irrigation system with a high drainage gate saved irrigation water and prevented herbicide runoff whereas the continuous irrigation and overflow scheme resulted in significant losses of water as well as the herbicides. Maintaining the excess water storage is important for preventing paddy water runoff during significant rainfall events. The organic carbon partition coefficient K_oc seems to be a strong indicator of the aquatic fate of the herbicide as compared to the water solubility (S_W). However, further investigations are required to understand the relation between K_oc and the agricultural practices upon the pesticide fate and transport. An extension of the water holding period up to 10 days after herbicide application based on the DT₉₀ from the currently specified period of 3-4 days in Japan is recommended to be a good agricultural practice for controlling the herbicide runoff from paddy fields. Also, the best water management practice, which can be recommended for use during the water holding period, is the intermittent irrigation scheme using an automatic irrigation system with a high drainage gate. © 2006 Elsevier B.V. All rights reserved.

Applicability of ELISA in pesticide monitoring to control runoff of bensulfuron-methyl and simetryn from paddy fields

The applicability of ELISA kits was evaluated as an alternative to monitor bensulfuron-methyl and simetryn behavior in paddy water under intermittent (Plot 1) and continuous (Plot 2) irrigation schemes. Simetryn concentrations in both plots decreased exponentially from the peak of the first day. However, the simetryn kit systematically underestimated by a factor of 0.79 as compared to the GC method. Bensulfuron-methyl concentrations exhibited similar dissipation kinetics in paddy water and the drainage water. The bensulfuron-methyl kit was capable of distinguishing spatial variations of concentrations in the paddy field. The ELISA kits clearly indicated differences in the loss of both herbicides between the two plots and therefore may be useful for evaluating the water management practice of pesticide runoff control in paddy fields.

Simulation of pesticide behavior in a paddy block by a pesticide fate and transport model

A simulation model (PCPF-B) was developed based on the PCPF-1 model to predict the runoff of pesticides from paddy plots to a drainage canal in a paddy block. The block-scale model now comprises three modules: (1) a module for pesticide application, (2) a module for pesticide behavior in paddy fields, and (3) a module for pesticide concentration in the drainage canal. The PCPF-B model was first evaluated by published data in a single plot and then was applied to predict the concentration of bensulfuron-methyl in one paddy block in the Sakura river basin, Ibaraki, Japan, where a detailed field survey was conducted. The PCPF-B model simulated well the behavior of bensulfuron-methyl in individual paddy plots. It also reflected the runoff pattern of bensulfuron-methyl at the block outlet, although overestimation of bensulfuronmethyl concentrations occurred due to uncertainty in water balance estimation. Application of water management practice such as water-holding period and seepage control also affected the performance of the model. A probabilistic approach may be necessary for a comprehensive risk assessment in large-scale paddy areas.

Behavior of pretilachlor and dimethametryn in water of flooded rice fields

In order to understand the behavior of pretilachlor, a popular rice herbicide in the world, and a synergetic active ingredient, dimethametryn, a monitoring study was conducted in 3 paddy plots in Kyushu region, Japan. The monitoring indicated different behaviors for both pesticides from those reported in the literature. Maximum concentrations of pretilachlor and dimethametryn were 1 order of magnitude lower than the values observed in previous studies. However, the dissipation rates estimated from monitoring data were in agreement with other studies in Japan. The pesticide product was tested and showed good dissolution of pretilachlor and dimethametryn in water, suggesting that another study is needed to explain the low concentrations of the two pesticides in the fields. Besides pesticide behaviors, it was observed from the monitoring that water management in paddy rice cultivation still requires more attention to reduce the environmental risk of rice pesticides.

Pesticide discharge and water management in a paddy catchment in Japan

Concentrations of several pesticides were monitored in a paddy block and in the Kose river, which drains a paddy catchment in Fukuoka prefecture, Japan. Detailed water management in the block was also monitored to evaluate its effect on the pesticide contamination. The concentrations of applied pesticides in both block irrigation channel and drainage canal increased to tens of μg/L shortly after their applications. The increase in pesticide concentrations was well correlated with the open of irrigation and drainage gates in the pesticide-applied paddy plots only 1–3 days after pesticide application. High concentration of other pesticides, mainly herbicides, was also observed in the inflow irrigation and drainage waters, confirming the popularity of early irrigation and drainage after pesticide application in the area. The requirement of holding water after pesticide application (as a best management practice) issued by the authority was thus not properly followed. In a larger scale of the paddy catchment, the concentration of pesticides also increased significantly to several μg/L in the water of the Kose river shortly after the start of the pesticide application period either in downstream or mid–upstream areas, confirming the effect of current water management to the water quality. More extension and enforcement on water management should be done in order to control pesticide pollution from rice cultivation in Japan.

Exposure risk assessment and evaluation of the best management practice for controlling pesticide runoff from paddy fields. Part 2: Model simulation for the herbicide pretilachlor

BACKGROUND: Monitoring studies revealed high concentrations of pesticides in the drainage canal of paddy fields. It is important to have a way to predict these concentrations in different management scenarios as an assessment tool. A simulation model for predicting the pesticide concentration in a paddy block (PCPF-B) was evaluated and then used to assess the effect of water management practices for controlling pesticide runoff from paddy fields. RESULTS: The PCPF-B model achieved an acceptable performance. The model was applied to a constrained probabilistic approach using the Monte Carlo technique to evaluate the best management practices for reducing runoff of pretilachlor into the canal. The probabilistic model predictions using actual data of pesticide use and hydrological data in the canal showed that the water holding period (WHP) and the excess water storage depth (EWSD) effectively reduced the loss and concentration of pretilachlor from paddy fields to the drainage canal. The WHP also reduced the timespan of pesticide exposure in the drainage canal. CONCLUSIONS: It is recommended that: (1) the WHP be applied for as long as possible, but for at least 7 days, depending on the pesticide and field conditions; (2) an EWSD greater than 2 cm be maintained to store substantial rainfall in order to prevent paddy runoff, especially during the WHP.

Engineering cellulose nanofibre suspensions to control filtration resistance and sheet permeability

This study examines and quantifies the effect of adding polyelectrolytes to cellulose nanofibre suspensions on the gel point of cellulose nanofibre suspensions, which is the lowest solids concentration at which the suspension forms a continuous network. The lower the gel point, the faster the drainage time to produce a sheet and the higher the porosity of the final sheet formed. Two new techniques were designed to measure the dynamic compressibility and the drainability of nanocellulose–polyelectrolyte suspensions. We developed a master curve which showed that the independent variable controlling the behaviour of nanocellulose suspensions and its composite is the structure of the flocculated suspension which is best quantified as the gel point. This was independent of the type of polyelectrolyte used. At an addition level of 2 mg/g of nanofibre, a reduction in gel point over 50 % was achieved using either a high molecular weight (13 MDa) linear cationic polyacrylamide (CPAM, 40 % charge), a dendrimer polyethylenimine of high molecular weight of 750,000 Da (HPEI) or even a low molecular weight of 2000 Da (LPEI). There was no significant difference in the minimum gel point achieved, despite the difference in polyelectrolyte morphology and molecular weight. In this paper, we show that the gel point controls the flow through the fibre suspension, even when comparing fibre suspensions with solids content above the gel point. A lower gel point makes it easier for water to drain through the fibre network,reducing the pressure required to achieve a given dewatering rate and reducing the filtering time required to form a wet laid sheet. We further show that the lower gel point partially controls the structure of the wet laid sheet after it is dried. Halving the gel point increased the air permeability of the dry sheet by 37, 46 and 25 %, when using CPAM, HPEI and LPEI, respectively. The resistance to liquid flow was reduced by 74 and 90 %, when using CPAM and LPEI. Analysing the paper formed shows that sheet forming process and final sheet properties can be engineered and controlled by adding polyelectrolytes to the nanofibre suspension.

Faecal incontinence in childhood : a multidisciplinary approach including biofeedback

One hundred and seven children with faecal incontinence were evaluated and managed over a 3 year period by a multidisciplinary team. After initial clinical assessment, evaluation of defaecatory mechanisms (using a balloon model) and assessment of personal-social development and self-concept were undertaken. Management was based on initial bowel evacuation, short-term laxatives, and habit training involving systematic use of positive reinforcement; 69 children received biofeedback conditioning. Idiopathic megacolon with constipation and soiling was the most common finding (98 cases). Other diagnoses included previously undiagnosed neurogenic bowel (three cases), post-surgical anal anomalies (four cases), and psychogenic encopresis (two cases). Idiopathic megacolon was characterized by decreased rectal sensation, increased threshold for external sphincter relaxation and an inability to evacuate. Faecal incontinence was associated with an undesirably low social self-concept (70% of the 40 evaluated), but was not related to a delay in development (mean general developmental quotient = 105 ± 8, for the 35 tested). Family psychopathology warranting referral for family therapy was found in 14 children (13%). The management programme yielded a short-term (3 months) cure rate of 68% and a long-term (12 months) cure rate of 90%, with 10% having continued soiling which varied from occasional to several incidents/week. No significant improvement in self-concept was observed overall, although marked improvements were observed in some children. We conclude that disordered defaecatory dynamics are a major determinant of faecal incontinence in children. Undesirably low social self-concepts but normal developmental ability accompany this condition. Management is facilitated by a multidisciplinary approach, acknowledging the role of both behavioural and physiological components of the problem. This approach is effective in eradicating soiling in the majority of cases, comparing favourably with other published data.

Review of the evidence of lymphedema treatment effect

Lymphedema treatment aims to alleviate symptoms, prevent progression and reduce risk of skin infection. Mainstream treatment options have been investigated in over 160 studies. Findings from these studies have been included in at least one of more than 20 literature reviews. A critique of these reviews was undertaken to summarise efficacy findings. The quality of the reviews was evaluated and gaps in the research identified, to better guide clinical practice. Overall, there was wide variation in review methods. The quality of studies included in reviews, in terms of study design and reporting overall has been poor. Reviews consistently concluded that complex physical therapy is effective at reducing limb volume. Volume reductions were also reported following the use of compression garments, pumps and manual lymphatic drainage. However, greatest improvements were reported when these treatments formed a combined treatment program. Large, well-designed, evaluated and reported randomised, controlled trials are needed to evaluate and compare treatments. Consistent outcome measures will allow better quality reviews and meta-analysis in the future.