Degradation and sorption of atrazine, hexazinone and procymidone in coastal sand aquifer media

Abstract

The degradation, sorption and transport of atrazine, hexazinone and procymidone in saturated coastal sand aquifer media were investigated in batch and column experiments. The pesticides were incubated with sterilised and non-sterilised groundwater or a mixture of groundwater and the aquifer material in the dark at 15 degrees C for 120 days. The estimated half-lives of the pesticides (and their ranges) in the mixture of groundwater and aquifer sand were 36 (31-40), 54 (40-77) and 84 (46-260) days for atrazine, procymidone and hexazinone, respectively. Compared with the relevant results for the groundwater-sand mixture phase, the estimated half-life of pesticides in the groundwater phase alone was shorter for procymidone (21 days) but longer for hexazinone (134 days); atrazine was not degraded in the groundwater phase. Chemical degradation appeared to have played the predominant role in the degradation of hexazinone and procymidone in the aquifer system, while both chemical and biological processes seemed to be important for the degradation of atrazine. Batch isothermal experiments were carried out at pH 4.6-4.7 to obtain sorption coefficients under equilibrium conditions. The isothermal data of the pesticides fitted well with the non-linear Freundlich function with an exponent of sorption coefficient that was greater than one. Contrary to reports in the literature, sorption of atrazine was the greatest, and procymidone was slightly more sorbed than hexazinone. A column experiment was conducted at a typical field-flow velocity of 0.5 m day(-1) over 60 days to study pesticide attenuation and transport in flow dynamic conditions. Retardation factors, R, derived from a two-site sorption/desorption model were 8.22, 1.76 and 1.63 for atrazine, procymidone and hexazinone, respectively. Atrazine displayed the lowest mobility and the mobility of procymidone was only slightly less than that of hexazinone, which is consistent with observations in the batch experiment. A possible explanation for these observations is that ionic atrazine is bound to oppositely charged ionic oxides, and ionic oxides have less effect on the sorption of the non-ionic procymidone. The significant tailing in the pesticide breakthrough curves (BTCs) in comparison with the bromide BTC, together with model-simulated results, suggests that the transport of the pesticides was under chemical non-equilibrium conditions with R values that were less than their equivalent values predicted using the batch equilibrium isothermal data. As a result of non-linear kinetic sorption, retardation factors of the pesticides in groundwater systems would not be constant and will decrease with decreasing pesticide concentrations and increasing flow velocities. Hence, the use of equilibrium isotherm data will probably over-predict the sorption of pesticides in groundwater systems. Rhodamine WT, a commonly used groundwater tracer, was significantly retarded (R = 5.48) and its BTC was much more spread out than the bromide BTC. Therefore, it would not be a good tracer for the...

Persistence of Atrazine and Alachlor in Ground Water Aquifers and Soil

“…Half-life estimates for atrazine range from 21 to 80 days (Winkelmann and Klaine, 1991;Smith and Walker, 1989); although Jones et al (1982) determined the half-life to be 330 and 385 days in two agricultural soils. Atrazine degradation is generally slower in the saturated environments Pang et al, 2005;Junk et al, 1984). Perry (1990) estimated the half-life for atrazine in a Kansas aquifer to be 1000 days.…”

HETEROGENEOUS PHOTO-FENTON REACTION OF A HERBICIDE ATRAZINE BY USING Fe(III)-TREATED HYDROXYAPATITES

“…[1][2][3][4] Although usage of ATZ has merits for enhancing grow and amount of crops and for facilitating being in good states of ground surfaces, relatively high chemical and biological stability of ATZ in soils and aquifers [5][6][7][8] potentially affords negative effect to crop contamination, 9 aquatic ecosystems, 10,11 and human health. [12][13][14][15] For keeping safety of natural waters, it is important to control ATZ usage amount 16 and to remove ATZ from natural waters.…”

Adsorption of Atrazine and Alachlor to Aquifer Material and Soil

“…Sorption isotherms are used to quantify the amount of chemical sorbed onto the solid phase (Pang et al, 2005;Lesan and Bhandari, 2003). The most common sorption isotherm used for pesticides is represented by the Freundlich equation:…”