Disappearance, pesticides

FIGURE 4.3 Loss of pesticides from soil, (a) Breakdown of herbicides in soil, (b) Disappearance of persistent organochlorine insecticides from soils (from Walker et al. 2000). 

The persistence of the N-nitrosamine that may be formed in soil will depend on a host of conditions, such as soil type, organic matter content, clay content, pH, the microflora present in the soil, moisture content and temperature, etc. Superimposed on all these factors will be the chemical nature of the pesticide. The N-nitrosoatrazine ( ) formed in soil from the herbicide atrazine ( ) was shown to be rapidly disappeared (1). Thus, in soil W-nitrosoatrazine was observed after one week, but was absent 4 and 10 weeks later (Table IV). In contrast, N-nitroso-butralin (11 ) persisted much longer than N-nitrosoatrazine (9) under the same conditions (Table V) and was still detectable after 6 months (3). Our studies demonstrated that N-nitrosoglyphosate is persistent in the soil. Fox soil treated with 20 ppm of nitrite nitrogen and 740 ppm glyphosate contained about 7 ppm of N-nitrosoglyphosate even after 140 days (6). 

The growing concealment of medical data during this period meant that the problem of food product contamination by pesticides disappeared from discussion. Over three five-year periods (from 1970 to the middle of the 1980s), Soviet society was almost completely deprived of information on human poisoning by food products contaminated with pesticides. However, the trend itself did not weaken. 

For example, in Tajikistan in 1980, more than 10% of local fish species were threatened by extinction as a result of poisoned bodies of water [3]. In the Nizhegorodsk oblast, 21 of 57 fish species disappeared by 1980, mainly due to the effects of agricultural run-off. On average, about 30% of the cases of fish death in freshwater reservoirs in the central belt of Russia are due to pesticide contamination of those bodies of water [1]. 

Danube, Ukrania 417,800 total 61,000 agriculture (rice more important) The cultures were a source of fertilizers and pesticides that have accumulated in the food chain causing physiological changes in animals and plants, as well as the disappearance of some species [37, 38]... 

Three general classes of hydrolytic reactions in aqueous solutions have been characterized. In neutral, or pH independent hydrolysis, the rate of disappearance of a pesticide, P, is given by... 

Recently reported results for the hydrolysis kinetics of chlorpyrifos (7 ) suggest that equation 2 may not be a valid representation of alkaline hydrolysis kinetics for at least one class of pesticides (organophosphorothioates). In short, kg may be pH dependent. However, disappearance kinetics for such molecules are still adequately described at fixed pH by pseudo first-order kinetics. 

Abiotic hydrolysis, sorbed pesticides, 221-43 Acetanilide herbicide, groundwater contamination, 299 Acid-catalyzed hydrolysis aldlcarb by RIEX, 257f kinetics, disappearance rate, 223 Acid hydrolysis, sorbed pesticides, 242... 

Bayesian methods are very amenable to applying diverse types of information. An example provided during the workshop involved Monte Carlo predictions of pesticide disappearance from a water body based on laboratory-derived rate constants. Field data for a particular time after application was used to adjust or update the priors of the Monte Carlo simulation results for that day. The field data and laboratory data were included in the analysis to produce a posterior estimate of predicted concentrations through time. Bayesian methods also allow subjective weight of evidence and objective evidence to be combined in producing an informed statement of risk. 

Table 9.2 Comparison of pseudo first-oraer rate constants for disappearance and initial rT OC elimination of different pesticides...

Either photocatalysis or ozonation alone achieved rapid disappearance of aromatic pesticide. In contrast, mineralization (TOC removal) was slow for both. However, photocatalytic mineralization was enhanced considerably by ozone pretreatment (Fig. 9.16).31) This effect may be explained by ozonolytic cleavage of the aromatic ring and subsequent formation of aliphatic compounds which are more degradable by photocatalysis. Simultaneous use of photocatalyst and ozonation (illuminated by 254 nm light) showed synergetic effect on TOC removal (Fig. 9.17).32) In this process scavenging of electrons by ozone is considered to play the most important role. 

During the fermentative process, yeasts can cause the disappearance of pesticide residues by degradation or absorption at the end of the fermentation when yeasts are deposited as lees. 

Hydrolysis can explain the attenuation of contaminant plumes in aquifers where the ratio of rate constant to flow rate is sufficiently high. Thus 1,1,1-trichloroethane (TCA) has been observed to disappear from a mixed halocarbon plume over time, while trichlo-roethene and its biodegradation product 1,2-dichloroethene persist. The hydrolytic loss of organophosphate pesticides in sea water, as determined from both laboratory and field studies, suggests that these compounds will not be long-term contaminants despite runoff into streams and, eventually, the sea (Cotham and Bidleman, 1989). The oceans also can provide a major sink for atmospheric species ranging from carbon tetrachloride to methyl bromide. Loss of methyl bromide in the oceans by a combination of hydrolysis... 

Table 6.4 shows first-order rate coefficients and tx/2 values for degradation of a number of pesticides in soils (Rao and Davidson, 1982). The k and t1/2 values calculated from field data are based on the disappearance of the parent compound (solvent extractable). Table 6.4 also includes k and t1/2 values calculated on mineralization (14C02 evolution) and parent-compound disappearance from laboratory studies. The t1/2 values were smaller for field than for laboratory studies. Rao and Davidson (1980) attribute this to the multitude of factors that can affect pesticide disappearance in the field while only one factor is studied in the laboratory. Rao and Davidson (1982) suggested that pesticides be classified into three groups based on values (Table 6.5) nonpersistent (t1/2 < 20 days), moderately persistent (20 < t1/2 < 100 days), and persistent (/1/2 > 100 days). Most chlorinated hydrocarbons are grouped as persistent, while carboxyl-kanoic acid herbicides are nonpersistent. The s-triazines, substituted ureas, and carbamate pesticides are moderately persistent. 

Their volatilization from litter on the forest floor will also be appreciable. With the possible exception of carbaryl, their volatilization after being washed into the soil will be relatively low or insignificant because of their low volatility, low Henry s constants, Kh> and/or their high rates of degradation in the soil environment. The rapid disappearance of the phenoxy herbicides (2, 31) and the insecticide, fenitrothion (28) from vegetation and the forest floor is supporting evidence that volatilization is an important pathway for loss of applied pesticides from the forest canopy and litter on the forest floor. 

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