Soils residues

El Beit lOD, Wheelock JV, Cotton DE. 1981a. Factors affecting soil residues of dieldrin, endosulfan, gamma-HCH, dimethoate, andPyrolan. Ecotoxicol Environ Safety 5 135-160. 

Lee JK, KS Kyung (1995) Uptake of 3,3, 4,4 -tetrachloroazobenzene (TCAB) soil residues by rice (Oryza sativa L.). J Agric Food Chem 43 519-523. 

Owing to its low water solubility and high octanol/water partition coefficients, dinitroaniline herbicides adsorb and bind to soil macromolecules and show minimal leaching potential. Dinitroanilines herbicides show good soil residue activities with soil half-lives ranging from 30 days for benfluralin and oryzalin to 6-7 months for trifluralin. Al-Dealkylation (aerobic conditions) and reduction of the nitro group to an amino moiety (anaerobic conditions) have been reported as major soil degradation pathways. 

Dinitroaniline herbicides are generally stable in soil. Residue methods were developed for both the parent molecule and selective soil degradates. 

Soil samples are extracted with buffered acetonitrile with a mechanical shaker. Alter centrifuging, aliquots of the extracts are amended with isotopically labeled internal standards and evaporated to dryness. The samples are reconstituted and analyzed by LC/MS/MS. This method determines soil residues of flucarbazone-sodium, sulfonic acid, sulfonamide and NODT with an LOQ of 0.001 mg kg for each analyte. 

The soil residue level is determined from the relative responses of the analytes to the internal standards. A five-point calibration curve is analyzed in triplicate, and the data are analyzed by a weighted 1 /x linear regression model. The calculated slope and intercept from the linear regression are used to calculate the residue levels in the soil samples. A 20% aliquot of the sample extract receives 10 ng of each internal standard... 

Transfer the concentrate from Section 6.1 to a 200-mL separatory funnel with 50 mL of water and add 10 mL of saturated aqueous sodium chloride solution. Extract twice with 100 mL of n-hexane. Dry the n-hexane extract by passing through about 80 g of anhydrous sodium sulfate on a glass funnel into a 500-mL separatory funnel for the rice samples and into a 500-mL round-bottom flask for the soil sample. Wash the anhydrous sodium sulfate with 30 mL of n-hexane and combine the washings into the vessel. The n-hexane extract of soil sample is evaporated to dryness under reduced pressure, then the soil residue is processed as described in Section 6.3.2. 

Anticipated persistence and mobility of agrochemical and degradates Anticipated variability in soil residues and cost constraints Depends upon specific analytical procedures (and associated LOQ) and available sample storage and processing capabilities Necessary for most dryland and irrigated cropping scenarios... 

Study indicates that residues are stable, any observed decline in soil residues can then be assumed to have occurred in situ. Details on the conduct of a freezer storage study are given in Section 4. 

DP-6 over 3000 soil samples collected from several terrestrial field dissipation studies. The sample procedural recoveries using this method, conducted concurrently with the treated samples during soil residue analysis, are summarized in Table 5. This method was proven to be short, rugged, sensitive, and suitable for measuring residues in soil and sediment at levels down to 0.01 mg kg . The reproducibility of the methods also indicated acceptable method performance and, as a result, thousands of samples were analyzed using this methodology. 

Dislodgeable soil residue (DSR) studies are used to determine exposure of re-entry workers to soil surface residues. Soil surface residues are defined as test substance residue levels in <150-q.m soil particles (i.e. soil dust which can stick to a worker s skin, or can be inhaled). 

Figure 1 was taken from an unpublished report, DuPont Study No. AMR 4392-97, Dissipation of Dislodgeable Foliar and Soil Residues of Oxamyl Following Application of Vydate L Insecticide to Tomatoes in the USA - Season 1997-1998 . This study has been submitted to the EPA and the data were used to establish and verify re-entry intervals. Data from this study will be used to provide an example of the topics discussed throughout this article. 

The polar character of neonicotinoids makes them, in general, potentially mobile in soil. Acetamiprid and nitenpyram have short soil persistence. Imidacloprid and thi-amethoxam, however, are sufficiently persistent in soil to be used for soil treatment. The definition of soil residues for the various neonicotinoid compounds except for imidacloprid are the parent compound and it metabolites. The metabolites of acetamiprid are lM-1-2, lM-1-4 and lC-0 (Figure 6). The metabolites of nitenpyram are 2-[N-(6-chloro-3-pyridyl-methyl)-A-ethyl]amino-2-methyliminoacetic acid (CPMA) and A-(6-chloro-3-pyridylmethyl)-Ai-ethyl-A -methylformamidine] (CPMF). 

Extraction of neonicotinoid residues from soil is much more difficult than their extraction from plant or water samples. Soil residues could exist as bound residue . Various extraction methods such as organic solvent extraction, supercritical fluid extraction (SEE), Soxhlet extraction and sonication have been used. Some extraction methods are described in the following. 

Organic solvent extraction. Two analytical methods for acetamiprid have been developed One method is for the parent only and the other determines the total residue of the parent and its metabolites (lM-1-2, lM-1-4 and lC-0). Air-dried soil (20-g equivalent dry soil) is weighed into a centrifuge tube and imidacloprid residue is extracted with 100 mL of methanol-0.1M ammonium chloride (4 1, v/v) using a mechanical shaker for about 30 min. After shaking, the tube is centrifuged at 8000 rpm for 2 min. The supernatant is filtered and the analysis of the soil residue is carried out in the same manner as described above for the parent compound. 

Bronson KF, Neue HU, Singh U, Abao EB. Automated chamber measurements of methane and nitrous oxide flux in a flooded rice soil Residue, nitrogen, and water management. Soil Sci. Soc. Am. J. 1997 61 981—987. 

Sheppard, C.R.C. and D.J. Bellamy. 1974. Pollution of the Mediterranean around Naples. Mar. Pollut. Bull. 5 42-44. Shore, R.F. 1995. Predicting cadmium, lead and fluoride levels in small mammals from soil residues and by species-species extrapolation. Environ. Pollut. 88 333-340. 

Paraquat adsorbed to soils is usually unavailable to crops. In the case of wheat (Triticum aestivum), effects from contaminated soils were negligible until soil residues surpassed 600 to 1000 kg/ha, causing growth reduction of 10%, or 1650 kg/ha, causing elevated residues in leaves but not in grain (Moyer and Lindwall 1985). 

Analysis of variance was used to assess the effects on polyaromatic hydrocarbons extraction at the 99% confidence level for the four factors varied. The percentage of 14C in the extract and soil residue does not total 100% because of degradation and volatilization during incubation and due to losses during analysis. The data are presented in Table 2.3 and represent the average of the three replicates for the extract or soil residue. 

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