Pesticides in the Rhône river delta (France): basic data for a field-based exposure assessment

The pesticide concentration levels flowing into paddy fields and surrounding lagoons of the Rhône river delta were investigated over a period of 6 months in 2004. Water samples were collected at the outlets of the major ditches and in the lagoons in order to study the seasonal variation in pesticide concentrations and the spatial contamination profile. Twenty four pesticides were monitored, mainly herbicides and insecticides. Rice pesticides accounted for 90% of the detection rates while the pesticides transported by the Rhône river water dissolved phase only accounted for 10%. Pretilachlor, oxadiazon, MCPA and bentazone herbicides were found at the highest frequencies into the effluent waters of ditches with maximum concentration levels of 1.2, 0.8, 2.5 and 1.6 microg/L, respectively. Only one insecticide, tebufenozide, was sporadically detected at a maximum concentration level of 0.12 microg/L. There were two main peaks of contamination. The first one in April corresponded to the use of pre-emergence herbicides (oxadiazon and pretilachlor) and the second one in June was related to the post-emergence herbicides (MCPA and bentazone). These concentration peaks were well correlated with the pesticide application period time and rapid pesticide transfer (1-2 weeks) from fields to lagoons were observed. Increased loads of the pre-emergence herbicides were induced by the specific management of paddy fields which includes water emptying of fields before and after rice seeding. Pesticide dissipation into the lagoons occurred very quickly and the duration of the exposure of non-target aquatic organisms to high pesticide concentrations (in total a few microg/L level) was no longer than 2 weeks. According to the physico-chemical properties of the chemicals, contrasting results were observed when studying the spatial variation in pesticide concentrations through the lagoons. The concentrations of bentazone and MCPA, two substances with high phototransformation abilities, quickly decreased between the ditches and the lagoons while the oxadiazon and pretilachlor concentrations were more homogeneous.

Runoff of pesticides from rice fields in the Ile de Camargue (Rhône river delta, France): field study and modeling

A field study on the runoff of pesticides was conducted during the cultivation period in 2004 on a hydraulically isolated rice farm of 120 ha surface with one central water outlet. Four pesticides were studied: Alphamethrin, MCPA, Oxadiazon, and Pretilachlor. Alphamethrin concentrations in runoff never exceeded 0.001 microg L(-1). The three other pesticides were found in concentrations between 5.2 and 28.2 microg L(-1) in the runoff water shortly after the application and decreased thereafter. The data for MCPA compared reasonably well with predictions by an analytical runoff model, accounting for volatilization, degradation, leaching to groundwater, and sorption to soil. The runoff model estimated that runoff accounted for as much as 18-42% of mass loss for MCPA. Less runoff is observed and predicted for Oxadiazon and Pretilachlor. It was concluded that runoff from rice paddies carries important loads of dissolved pesticides to the wetlands in the Ile de Camargue, and that the model can be used to predict this runoff.

Pesticide by-products in the Rhône delta (Southern France). The case of 4-chloro-2-methylphenol and of its nitroderivative

A field monitoring campaign for pesticides and their transformation intermediates was carried out in the Rhône delta (Southern France). It was evidenced the following transformation sequence: MCPA-->4-chloro-2-methylphenol (CMP)-->4-chloro-2-methyl-6-nitrophenol (CMNP). Interestingly CMP disappeared about as quickly as MCPA, while CMNP was environmentally more persistent than the parent molecules. This is very relevant to the environmental risk associated with the occurrence of these compounds, because the nitration of chlorophenols reduces their acute toxicity but the nitroderivatives could have more marked long-term effects, associated with their genotoxicity. Irradiation experiments suggested that the photonitration of CMP into CMNP involves nitrogen dioxide, generated from the photolysis of nitrate and from the photooxidation of nitrite by ()OH. The photochemistry of Fe(III) species could also play a significant role, but its contribution is still difficult to be quantified. Another important intermediate of CMP transformation is methylnitrophenol (MNP), produced via a dechlorination/nitration pathway, with ortho-cresol as the most likely reaction intermediate.

Laboratory and field evidence of the photonitration of 4-chlorophenol to 2-nitro-4-chlorophenol and of the associated bicarbonate effect

BACKGROUND, AIM AND SCOPE

Photochemical processes can decontaminate the aqueous environment from xenobiotics, but they also produce secondary pollutants. This paper presents field and laboratory evidence of the transformation of 4-chlorophenol (4CP) into 2-nitro-4-chlorophenol (2N4CP).

MATERIALS AND METHODS

Field monitoring of 4CP and 2N4CP was carried out by solid phase extraction coupled with liquid chromatography-multiple reaction monitoring mass spectrometry. Laboratory irradiation experiments were carried out under a UV-Vis lamp, and the time evolution of the compounds of interest was followed by liquid chromatography.

PURPOSE

The purpose of this study was elucidating the pathways leading to 2N4CP from 4CP in paddy field water.

RESULTS AND DISCUSSION

The field monitoring results suggest that 4CP can be transformed into 2N4CP in the paddy field water of the Rhône delta (Southern France). The laboratory study indicates that the transformation can take place via photonitration by (*)NO(2). The nitration process is inhibited by bicarbonate, possibly due to basification that favours the occurrence of the 4-chlorophenolate. The latter could consume (*)NO(2) without being nitrated. Photonitration in the presence of bicarbonate could account for the observed transformation in the field.

CONCLUSIONS

Photonitration of 4CP to 2N4CP by (*)NO(2) could account for the observed interconversion of the two compounds in paddy fields. The results are of concern because 2N4CP is biorecalcitrant and toxic.

RECOMMENDATIONS AND PERSPECTIVES

Bicarbonate can modulate the photonitration of 4CP into 2N4CP, which can be very significant in bicarbonate-poor waters.

Comparing pharmaceutical and pesticide loads into a small Mediterranean river

During 2003/2004, water samples were collected upstream and downstream of two wastewater treatment plant (WWTP) outlets in order to determine the contribution of urban centres to concentration of selected pharmaceuticals (antiphlogistics, lipid regulators and carbamazepine) and pesticides into a Mediterranean river basin (Arc river, Aix en Provence, France). Pharmaceutical loads were compared to pesticide ones. They could be nearly regarded as important as pesticide ones at least at one sampling site. The observed pollution patterns differed from pesticides to pharmaceuticals. Pesticide pollution occurred through a high pollution peak in spring while pharmaceuticals were continuously infused into the river via WWTP effluents. Carbamazepine and bezafibrate were detected in almost all samples at concentration levels ranging from ng/L to microg/L. The major pharmaceutical source could be ascribed to WWTP effluents and pharmaceutical concentrations increased during low flow rate conditions (summer), when municipal wastewater effluents accounted for the majority of the river water flow. Treated wastewaters contributed to a lesser extent to pesticide river water pollution. In an urbanized Mediterranean river basin, a deep understanding of water pollution by organic waste contaminants is required in order to set up an efficient programme of pollution reduction measures.