Half-life atrazine

In a soil-core microcosm study, Winkelmann and Klaine (1991) observed that the concentration of atrazine decreased exponentially over a 6-month period. Metabolites identified in soil included desethylatrazine, deisopropylatrazine, didealkylatrazine, and hydroxyatrazine. The half-life in soil... 

A facultative anaerobic bacterium isolated from a stream sediment utilized atrazine as a carbon and nutrient source. Microbial growth was observed but no degradation products were isolated. At 30 °C, the half-life was estimated to be 7 d (Jessee et ah, 1983). 

The dye-sensitized photodecomposition of atrazine was studied in aqueous, aerated solutions. When the solution was irradiated in sunlight for several hours, 2-chloro-4-(isopropyl-amino)-6-amino-s-triazine and 2-chloro-4-(isopropylamino)-6-acetamido-s-triazine formed in yields of 70 and 7%, respectively (Rejto et al, 1983). Continued irradiation of the solution led to the formation of 2-chloro-4,6-diamino-s-triazine which eventually degraded to unidentified products. Hydroxyatrazine was the major intermediate compound formed when atrazine (100 mg/L) in both oxygenated estuarine water (Jones, 1982 Mansour et ah, 1989) and estuarine sediments were exposed to sunlight. The rate of degradation was slightly greater in water (half-life 3-12 d) than in sediments (half-life 1-4 wk) (Jones et al., 1982). 

Chemical/Physical. The hydrolysis half-lives of atrazine in aqueous buffered solutions at 25 °C and pH values of 1, 2, 3, 4, 11, 12 and 13 were reported to be 3.3, 14, 58, 240, 100, 12.5, and 1.5 d, respectively (Armstrong et al., 1967). Atrazine does not hydrolyze in uncatalyzed solutions, even under elevated temperatures. The estimated half-life of atrazine in neutral, uncatalyzed water at pH 6.97 and 25 °C is 1,800 yr. Under acidic conditions, hydrolysis proceeds via mono- and diprotonated forms (Plust et al., 1981). Atrazine is stable in slightly acidic or basic media, but is hydrolyzed to hydroxy derivatives by alkalies and strong mineral acids (Windholz et al., 1983). Atrazine reacts with strong mineral acids forming hydroxyatrazine (Montgomery and Freed, 1964). 

The persistence (half-life) of atrazine in the subsurface is governed by chemically and biologically mediated transformations. Because the solubility of atrazine is relatively high ( 30mg/L) compared to its toxicity level in water (5 Lig/L), atrazine has become a hazard to groundwater quality. Atrazine has been detected in groundwater more than any other crop protection chemical two examples of atrazine persistence-transformation in aquifer environments are discussed next. 

In the field, atrazlne has been found to have a half-life of <1 month, but the half-life is affected by the tillage system (44-46), the agricultural soil ammendments and soil pH (45-48), and soil organic matter (49). In another study, atrazine and hydroxyatrazlne have been found to persist into the following growing season (50). 

Illustrative Example 16.2 Estimating the Indirect Photolysis Half-Life of Atrazine in a Shallow Pond Reactions with Singlet Oxygen ( 02)... 

The indirect photolysis half-life of atrazine (assuming that reaction with HO is the dominant process) is then given by (Eq. 16-7) ... 

Estimating the Indirect Photolysis Half-Life of Atrazine in a Shallow Pond... 

CDAT and CAAT. Excess H202 resulted in slower degradation of atrazine and followed pseudo first-order kinetics. The half-life (f1/2) of atrazine at a FeS04 H202 ratio of 1 100 was 1.9 hr. Table 6.8 lists the half-lives of atrazine according to various technologies. 

Some currently used pesticides that are intermediate in water solubility and persistence can reach fairly high concentrations in water, sediment, and biota, in areas of high use. Pesticides that enter the lakes—whether by direct discharge along the shores, by runoff through tributaries, or from the atmosphere—are retained in the system and become more concentrated over time. For example, atrazine is detected widely in streams in the midwestern USA at concentrations in the range of several hundred ng/L to several tens of xg/L [12]. The half-life of atrazine in deeper lakes was estimated to be greater than 10 years. 

Although atrazine has a soil half-life of 30-90 days, transport out of this zone into receiving waters leads to longer half-lives [101]. For pesticides with high water solubilities, such as atrazine, tributary inputs can be a major source, and environmental response to sources is controlled by long hydraulic residence times and slow transformation rates. Despite the fact that only 1% of the applied atrazine is lost by transport to rivers and lakes, and another 1% by aerial transport, the large quantities applied, together with efficient hydraulic transport result in accumulation in aquatic systems. 

The primary use of prometon, introduced in 1959, is for total vegetation control in noncrop areas around the farm, on industrial sites, and for use in and under asphalt. Application rates are from 10 and 601b/A/yr (11 and 67kg/ha/ yr), 10 to 30 times higher than for atrazine, but the treated areas are much smaller (Capel et al, 1999). Prometon is highly persistent with an average field half-life of 500 days. 

The use of solar powered systems for destruction of a mixture of pesticides in well water including dichloroaniline, benzopyran, atrazine, propazine, alachlor, prometryn, bromacil and cyanobenzoate has been achieved [124], Variable efficiencies for the decomposition of these compounds was observed with over 90% of dichloroaniline destroyed in 10 h compared to 50% of propazine in the same period. In general for most of the pesticides examined the half life time for the process in the 100 ppb concentration range was less than 1 h. 

I- m depth) are installed in a container that allows collecting the water that leaches through the soil core. This water (leachate) is analyzed for content of parent substance and metabolites. If any substance exceeds a concentration of 100 ngA (=0.1 ppb), high risk for leaching is established and the substance cannot be used in the field. Also, here the formation of degradation products must be taken into account. They are often more polar than the parent and are therefore more soluble in water. This can lead to higher mobility. Atrazine is a typical example. The parent molecule has already a tendency to leach into groundwater where it has a half-life of 100 to 200 days. Its metabolite desethylatrazine (DEA, Eq. 

The half life of atrazine in the soil to give nonphytotoxic products varies from 60 days to more than a year.68 The herbicide alachlor is present at low levels in groundwater in 16 states. It is classed as a probable human carcinogen. It is degraded to a variety of products in soil... 

Triazine herbicides are moderately persistent in soils and water (10-18 months) with atrazine being one of the more persistent of the group. Laboratory and field data have shown that the disappearance of atrazine from soil is influenced by temperature, pH, moisture content, and organic matter content the effect of temperature and pH on the half-life of atrazine in... 

In conclusion, atrazine has been found to be a regular contaminant of groundwater. The detection of concentrations above the EEC standard was very frequent in northern Italy before the ban and due to its persistence in deep soil and groundwater (half-life in the order of years), such detections are even now not rare events. This justifies the need for control measures at least in areas at higher risk. The total national ban was the consequence of an emotional situation, determined more by public fear than by sound scientific evaluation. Therefore, probably, it was not the best solution. 

The purpose of the Italian han on atrazine was to remove from use a chemical that had already accumulated to unacceptable levels in the environment and also to provide incentives to manufacturers to produce chemicals with lower accumulative abilities. Figure 8.5 shows GU S indices for 14 herbicides. The GU S index indicates the ability of an agricultural chemical to accumulate in groundwater, and has two components. The water solubility of a chemical is measured by its partition coefficient The higher the coefficient, the less soluble is the chemical in water. Degradability of the chemical is measured by the (logarithm of the) half-life in sou (t ). The GU S index is then defined by GU S = log ty A - log her-... 

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