Sampling field

The following data were obtained for the repetitive spike recoveries of field samples. ... 

Subdivision O guidelines for residue chemistry data were originally pubHshed by the EPA in 1982. These have been supplemented to improve the rate of acceptance by EPA reviewers of the many reports submitted by registrants in support of tolerances for pesticides in foods. The residue chemistry studies most frequently rejected include metaboHsm in plants, food processing (qv) studies, and studies on storage stabHity of residues in field samples (57). AH tolerances (maximum residue levels) estabHshed under FIFRA are Hsted in 40 CFR under Sections 180 for individual pesticides in/on raw agricultural commodities, 180 for exemptions from tolerances, 185 for processed foods, and 186 for animal feeds. 

Membrane extraetion ean also be a basis for environmental field sampling and for determination of freely available fraetions of both metal ions and organie eompounds. Proeedures and deviees for this ai e developed, as will be deseribed in the presentation. 

Several manual and continuous analytical techniques are used to measure SO2 in the atmosphere. The manual techniques involve two-stage sample collection and measurement. Samples are collected by bubbling a known volume of gas through a liquid collection medium. Collection efficiency is dependent on the gas-liquid contact time, bubble size, SO2 concentration, and SO2 solubility in the collection medium. The liquid medium contains chemicals which stabilize SO2 in solution by either complexation or oxidation to a more stable form. Field samples must be handled carefully to prevent losses from exposure to high temperatures. Samples are analyzed at a central laboratory by an appropriate method. 

Approximate allowable bearing pressures on sedimentary rock and soils may be taken from Table 2-31 [1 and 37]. Where questionable surface and subsurface soil conditions exist allowable bearing pressures can be determined with the aid of field sampling, field tests (both surface and subsurface through borings), and laboratory tests. 

Cu Acute toxicity on biofilms EC50 ( C) 20-50 (spring) 100-350 (summer) EC50 (Y) 230 (low P) 718 (highP) EC50 (Fo) 56-92 (low P) 196-206 (high P) Field samples Ter river" Fluvial microcosms Field samples"... 

Zn Acute toxicity on Effect >65 X 10" Field samples Dommel, metal... 

PCDDs and PCDEs, together with coplanar PCBs, can express Ah-receptor-mediated toxicity. TCDD (dioxin) is used as a reference compound in the determination of TEFs, which can be used to estimate TEQs (toxic equivalents) for residues of PHAHs found in wildlife samples. Biomarker assays for Ah-receptor-mediated toxicity have been based on the induction of P450 lAl. TEQs measured in field samples have sometimes been related to toxic effects upon individuals and associated ecological effects (e.g., reproductive success). 

In experiments using field samples containing natural assemblies of microorganisms, at least two effects of supplementation with nitrogen or phosphorus have been encountered ... 

Voordouw G, JK Voordouw, RR Karkhoff-Schweiser, PM Eedorak, DWS Westlake (1991) Reverse sample genome probing, a new technique for identification of bacteria in environmental samples by DNA hybridization, and its application to the identification of sulfate-reducing bacteria in oil field samples. Appl Environ Microbiol 57 3070-3078. 

The anaerobic dechlorination of PCBs has been extensively studied both in microcosms and in field samples from heavily contaminated sites in the United States. Three main patterns have been fonnd—N that removed flanked meto-chlorines, P that removed para-chlorines, and LP that removed nnflanked para-chlorines (Bedard et al. 1998). By contrast, ort/to-chlorines were more recalcitrant. These experiments, which have been discussed in Chapter 9, Part 2, laid the fonndation for analysis of a field situation and an appreciation of the effect of long-term exposnre of contaminated lake sediment (Magar et al. 2005a,b). Substantial dechlorination took place in buried sediment cores (35-40 cm) compared with the snrface sediment cores (0-5 cm). Although there were some variations among the cores, the di- and trichlorinated biphenyls were produced at the expense of the... 

The hydrogeological and QA/QC aspects of hazardous waste field investigations are fairly well advanced. Yet needed, however, is a systematic approach to the design of field sampling, to the selection of compounds for analysis, and to the methods for interpretation of analytical data. 

TCDD). The majority of these samples have been collected and analyzed at an average cost of 700 per sample. This includes per diem, labor, equipment, expendable supplies, transportation, and 400 per analysis by contract laboratories. An evaluation of this data has suggested that field sampling and sample handling methods have a significant impact upon the precision and accuracy of the resulting data which, in turn, impact the cost and feasibility of various remedial options. 

Precision. The choice of 400 mg of soil is arbitrary. It was chosen in order to keep the entire cleanup step within a 2 cc vial. A test of replication was done on one field sample contaminated with about 20,000 ppm of 1254. Three samples of 50, 54, and 54 mg were weighed into separate vials, extracted, and then diluted 1 1000 into hexane in a separate vial. The three chromatograms are shown in Figure 7. Two peaks were quantified to demonstrate how reproducible a measurement can be, even in a field sample. 

When testing and analysis are completed, the data can be analyzed and summarized. Statistical methods are often used during this step In a study. Data should first be edited and validated. Quality assurance Information from both the sampling and laboratory analyses should be considered In this validation. Field sampling personnel and laboratory scientists should maintain responsibility for data validation. 

J. A. Cruze and D. O. Hitzman. Microbial field sampling techniques for MEOR (microbial enhanced oil recovery) processes. US DOE Fossil-energy RepNIPER-351 CONF-870858, September 1987. 

The more a source material is processed the less it behaves and reacts like a typical field sample, and if a real-world contaminated soil is ground to reduce the particle size the heat of friction/shearing may alter the composition and constituents may volatilize. 

Repeatability is defined as precision under conditions where independent test results are obtained with the same method on identical test material in the same laboratory by the same operator using the same equipment within short intervals of time. The replicate analytical portion for testing can be prepared from a common field sample containing incurred residues. This approach is used extremely rarely. Normally, repeatability is estimated by the relative standard deviation ofrecoveries, which should be lower than 20% per commodity and fortification levels according to SANCO/825/00. In justified cases, higher variability can be accepted. 

Guidelines for the methods of sample collection of crop samples are detailed in the Codex Alimentarius, but generally in most instances crop samples should be representative of the crop being grown. As a general rule, the quantity of sample required is a minimum of 12 units or >1 kg of field sample, e.g., potato mbers, cabbages, etc. Samples selected should not be damaged or suffer from severe defects, disease symptoms, or other abnormalities. 

When choosing sampling locations and methods, take into account the factors which influence the crop, e.g., the plant morphology, differences in plant growth, the way the plot was treated, etc., all of which have an influence on the distribution of residues both on individual plants and in the trial plot as a whole. The actual material required to produce a field sample can be selected, as a rule, by one of the following methods ... 

Where trials are required to investigate the possible residue of test item in processed samples, e.g., juice, purde, etc., a larger quantity of the field sample must be collected. To collect this larger sample size, the size of the plots must often be increased at the... 

The samples should be analyzed as soon as possible after they have been taken, before physical or chemical changes can occur. For this reason, any intermediate storage of nonfrozen field samples should be avoided as far as possible, and dispatch of samples to the receiving laboratory should, as a general rule, take place immediately after sampling. 

A system of record keeping must be used which eliminates any risk of confusing the samples. As a rule, samples should be recorded immediately after their arrival and, especially in the case of nonfrozen field samples, prior to preparation for analysis. A record should also be kept of the condition of the samples upon arrival at the receiving laboratory and of any packaging or labeling defects. 

A second approach to determining freezer storage stability involves the reanalysis of incurred residues found in actual samples that are stored over time. Using this approach, soil from an actual field sample containing residues is periodically analyzed... 

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