Pesticide concentrations

For those pesticides that are cometabolized, ie, not utilized as a growth substrate, the assumption of first-order kinetics is appropriate. The more accurate kinetic expression is actually pseudo-first-order kinetics, where the rate is dependent on both the pesticide concentration and the numbers of pesticide-degrading microorganisms. However, because of the difficulties in enumerating pesticide-transforming microorganisms, first-order rate constants, or half-hves, are typically reported. Based on kinetic constants, it is possible to rank the relative persistence of pesticides. Pesticides with half-hves of <10 days are considered to be relatively nonpersistent pesticides with half-hves of >100 days are considered to be relatively persistent. 

Sorbed pesticides are not available for transport, but if water having lower pesticide concentration moves through the soil layer, pesticide is desorbed from the soil surface until a new equiUbrium is reached. Thus, the kinetics of sorption and desorption relative to the water conductivity rates determine the actual rate of pesticide transport. At high rates of water flow, chances are greater that sorption and desorption reactions may not reach equihbrium (64). NonequiUbrium models may describe sorption and desorption better under these circumstances. The prediction of herbicide concentration in the soil solution is further compHcated by hysteresis in the sorption—desorption isotherms. Both sorption and dispersion contribute to the substantial retention of herbicide found behind the initial front in typical breakthrough curves and to the depth distribution of residues. 

Wauchope RD, Leonard RA. 1980. Maximum pesticide concentrations in agricultural mnoff A semiempirical prediction formula. J Environ Qual 9 665-672. 

E1 Beit lOD, Wheelock JV, Cotton DE. 1981c. Factors involved in the dynamics of pesticides in soils The effect of pesticide concentration on leachability and adsorption. Int J Environ Stud 16 181-187. 

Preliminary Literature Review of the Impacts of Water Treatment on Pesticide Removal and Transformations in Drinking Water, in Progress Report on Estimating Pesticide Concentrations in Drinking Water and Assessing Water Treatment Effects on Pesticide Removal and Transformation a Consultation, Session VI. USEPA, Washington, DC (2000). Also available on the World Wide Web http //www.epa.gov/scipoly/sap 000/index.htm, accessed September 2002. 

ILSl, A Framework for Estimating Pesticide Concentrations in Drinking Water for Aggregate Exposure Assessments, Workshop Report 5/19/99. International Life Sciences Institute, Washington, DC (1999). 

The effects of water temperature and pesticide concentration on pesticide recoveries were tested by Moye et al The pesticides included alachlor, atrazine, bromacil, chlorothalonil, chloropyrifos, diazinon, endosulfan, simazine and trifluralin. Temperatures of 5,25,45 and 65 °C were tested and concentrations of 0.1,1.0 and 10 pgL were used. Water temperature had a pronounced effect on the recoveries whereas the concentration did not seem to have as great an effect. 

Pesticide concentrations in earthworms displayed regional differences. Such differences are likely to be observed in other potential food items. Earthworm exposure was log-normally distributed with the highest concentration being 163 qgg which represents the 97th percentile of diazinon found in earthworms from all sites. The geometric mean diazinon concentration in earthworms from PA was 2.56 agg (CL95 = 1.62. 06qgg ), and from WA was 0.046 xgg ... 

Distributions of pesticide concentrations in potential food items for avian species are required to estimate the contribution of food to exposure of birds in different regions where the test chemical may be used. On treated fields, detectable CEF residues were found in 102 of 207 earthworm samples. No earthworm samples collected from control fields (N = 28) contained detectable CEF. Average CEF concentrations in earthworms reached maxima 1-4 days post-application (Table 3). Mean CEF residues in earthworms fell below 0.1 qg g after 8 days post-application. This... 

The data in Table 4.4 show the result of global pesticide contamination. These pesticides were never used in the Arctic nevertheless, they were found in humans. It is notable that pesticide concentrations in human blood were several times higher (and in the case of befa-HCH, 17 times higher) in Russia than in Sweden and Norway. 

In AChE-based biosensors acetylthiocholine is commonly used as a substrate. The thiocholine produced during the catalytic reaction can be monitored using spectromet-ric, amperometric [44] (Fig. 2.2) or potentiometric methods. The enzyme activity is indirectly proportional to the pesticide concentration. La Rosa et al. [45] used 4-ami-nophenyl acetate as the enzyme substrate for a cholinesterase sensor for pesticide determination. This system allowed the determination of esterase activities via oxidation of the enzymatic product 4-aminophenol rather than the typical thiocholine. Sulfonylureas are reversible inhibitors of acetolactate synthase (ALS). By taking advantage of this inhibition mechanism ALS has been entrapped in photo cured polymer of polyvinyl alcohol bearing styrylpyridinium groups (PVA-SbQ) to prepare an amperometric biosensor for... 

Finally, the pesticide concentrations determined in water and biota, together with the toxicity values of each individual compound, the toxicity data measured in the water samples, and the general physicochemical values were combined and analyzed together to establish potential cause-effect relationships and identify major toxicants or environmental pressures in the area of study. More details can be found in Kock et al. [12],... 

Comparison of the pesticide concentrations (ng/L) found in this study in sites HDCD and HD AD with those measured in a previous study performed in 2005 in the same sampling sites [ 16, 20] showed a general good agreement for all pesticides except for bentazone, MCPA, propanil, and atrazine, which presented now comparatively lower concentrations, and alachlor, malathion, diuron, and molinate, whose concentrations have increased considerably (Fig. 3). 

These experimental toxicity values were compared with the theoretical toxicity units calculated for each sample and organism from the pesticide concentrations measured in the samples and their toxicity (50% effective concentration, EC50) towards the corresponding test organisms [12]. This comparison, which is illustrated in Fig. 6, gives an estimation of the extent to which the pesticides measured contribute to the observed experimental toxicity as well as about their relative contribution to it. 

Fig. 3 Comparison of pesticides concentrations (ng/L) reported for sites HDCD and HD AD in this study (average of 18 measurements performed between April and June 2008) and in a previous one (average of four measurements performed monthly between May and August 2005) [16, 20]...

In shellfish only three of the eight compounds monitored were detected feni-trothion, which was found in a mussel sample at 3.46 mg/kg, malathion, found in an oyster sample at 53.12 mg/kg, and the malathion degradation product malaoxon, which was found in one oyster and two mussel samples at concentrations between 2.53 and 4.59 mg/kg. As it can be seen in Fig. 7, positive samples (five of ten analyzed) were found in both bays and in scattered days along the period of study, with the sample showing the highest pesticide concentration (53.12 mg/kg of malathion in oysters collected from the northern bay on May 27) coinciding with the period of shellfish mortality. 

Seventy-three soil samples from 0-to-5 cm depth along the N-S transect collected by ultraclean methods were analyzed for selected organochlorine pesticides. Only three of the samples had pesticide concentrations greater than the detection limit of the analytical method. 

The toxic effects of pesticides can be diverse and depend on the sensitivity of organisms to these toxicants, and the pesticide concentration or bioavailability. Typically, the short- and long-term effects of pesticides have been evaluated through acute or chronic toxicity bioassays, respectively, using lethality endpoints and sublethal endpoints (e.g., growth and reproduction), particularly these last in chronic bioassays. 

Goldberg [48] studied the relationship between pesticide concentrations in water and in sediments and its dependence on the specific surface area of the sediment. 

Goldberg [48] has developed equations relating pesticide concentration in water, pesticide concentration in sediment and surface area of sediment they can be use to give an approximate estimation of the concentration of pesticides in water at concentrations below those measurable with available analytical equipment. 

A rag that a farmer was using was analyzed for pesticide residue. The rag weighed 49.22 g and yielded 25.00 mL of an extract solution that was determined to have a pesticide concentration of 102.5 ppm. How many grams of pesticide were in the rag and what is the concentration of pesticide in the rag in parts per million ... 

For the determination of these compounds a binding inhibition immunoassay, consisting of the competitive immunoreaction of the unbound antibody present in an analyte-antibody mixture with the hapten derivative immobilized at the sensor surface, has been applied. With the aim of assuring the regeneration and reusability of the surface without denaturation of the immobilized molecule, the formation of an alkanethiol monolayer was carried out to provide covalent attachment of the ligand to the functionalized carbodiimide surface in a highly controlled way. For DDT, the assay sensitivity was evaluated in the 0.004 - 3545 pg/l range of pesticide concentration by the determination of the limit of detection 0.3 pg/1 and the I50 value 4.2 pg/1. 

Radomski JL, Deichmann WB, Clizer EE, et al. 1968. Pesticide concentrations in the liver, brain, and adipose tissue of terminal hospital patients. Food Cosmet Toxicol 6 209-220. 

In the Ebro river zone (NE Spain), pesticide concentrations in groundwater were much higher than in the Llobregar river area. Hildebrandt et al. [18, 19] found in groundwater samples collected in 2000-2001 very high levels of metolachlor (10-2000 ng/L) and triazines (2460, 1980, 1270, 790 and 540 ng/L for atrazine, DEA, terbuthylazine, DIA and simazine, respectively). However, 3 years later (2004), triazines concentrations decreased dramatically, whereas metolachlor presented levels even higher (from 2,000 to 5,370 ng/L). 

---