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SPECIAL SECTION: FROM FIELD- TO LANDSCAPE-SCALE VADOSE ZONE PROCESSES

Basin-Scale Risk Assessment in Rice Paddies

An Example Based on the Axios River Basin in Greece

^a Univ. Cattolica del Sacro Cuore, Istituto di Chimica Agraria ed Ambientale, Sezione Chimica Vegetale, Via E. Parmense 84, Piacenza 29100, Italy
^b Aristotle Univ. of Thessaloniki, Lab. of Pesticide Science, Thessaloniki 54124, Greece
^* Corresponding author (dimitrios.karpouzas{at}unicatt.it)

Received 8 February 2005.

RICE (Oryza sativa L.) is cultivated in large river basins in Europe, where high loads of applied herbicides have resulted in the contamination of related surface water (SW) and groundwater (GW) systems. Therefore, risk assessment of pesticides used on rice should be performed at the basin scale. This study reports the development and validation of a basin-scale scenario, representative of rice cultivation in the main rice cultivation area in Greece, the Axios river basin. Soils of the rice-cultivated region of the basin are characterized as heavy clay, clay loams with poor infiltration. A 2000-ha rice-cultivated basin was simulated consisting of rice management blocks (200 ha) associated with drainage canals and a cross-linked river. This system was conceptualized using a combination of rice water quality (RICEWQ 1.6.2v) and river water quality (RIVWQ 2.02) models. Application of RICEWQ 1.6.2v for a 20-yr simulation period showed that the 90th percentile of the annual GW predicted environmental concentrations (PECs) for the herbicides propanil (3',4'-dichloropropionanilide) and molinate (S-ethyl perhydroazepine-1-carbothioate) were 3.2 fg L^–1 and 1.9 pg L^–1, respectively, suggesting low risk to GW. Pesticide mass and water releases from simulated paddies were utilized as inputs for canals and river, and the fate of propanil and molinate was simulated with the RIVWQ model. Comparison of the 90th percentile of maximum daily river PECs with the maximum measured concentrations of propanil and molinate in the Axios river in 1994 revealed acceptable agreement in both the magnitude of values and their temporal distribution. In general, the 90th percentiles of the maximum daily PECs of propanil in both canals (1.96 µg L^–1) and rivers (1.15 µg L^–1) were markedly lower than the corresponding PECs of molinate (6.07 and 0.394 µg L^–1, respectively). Increases in the period of paddy closure after application of molinate resulted in reduced SW PECs, suggesting that the selection of water management practices should be done according to pesticide persistence and local agronomic conditions.

Abbreviations: DAS, days after seeding • DAT, days after treatment • DCT, days of closure time • FOCUS, FOrum for the Coordination in the USe of models • GAP, good agricultural practice • GW, groundwater • Med-Rice, Mediterranean Rice Group • PEC, predicted environmental concentration • RICEWQ, Rice Water Quality model • RIVWQ, River Water Quality model • SW, surface water • TER, toxicity exposure ratio • VADOFT, vadose zone flow and transport model

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				D. L. Corwin, J. Hopmans, and G. H. de Rooij From Field- to Landscape-Scale Vadose Zone Processes: Scale Issues, Modeling, and Monitoring Vadose Zone J., March 8, 2006; 5(1): 129 - 139. [Abstract] [Full Text] [PDF]