Groundwater matrix effects

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Solve the tanker truck spill problem of Example 2.2 using explicit, central differences to predict concentrations over time in the groundwater table. Compare these with those of the analytical solution. The mass spilled is 3,000 kg of ammonia over 100 nf, and the effective dispersion coefficient through the groundwater matrix is 10 m2/s. 

Figure 5-3 shows a strong matrix effect in the analysis of perchlorate (CIO4 ) by mass spectrometry. Perchlorate at a level above 18 p,g/L in drinking water is of concern because it can reduce thyroid hormone production. Standard solutions of C104 in pure water gave the upper calibration curve in Figure 5-3. The response to standard solutions with the same concentrations of CIO4 in groundwater was 15 times less, as shown in the lower curve. Reduction of the ClOj" signal is a matrix effect attributed to other anions present in the groundwater.

Cheng J, Vecitis CD, ParkH, Mader BT, Hoffmann MR (2010) Sonochemical degradation of perfluorooctane suUrmate (PFOS) and perfluorooctanoate (PFOA) in groundwater kinetic effects of matrix inOTganics. Environ Sci Technol 44(l) 445-450... 

For pesticide residue immunoassays, matrices may include surface or groundwater, soil, sediment and plant or animal tissue or fluids. Aqueous samples may not require preparation prior to analysis, other than concentration. For other matrices, extractions or other cleanup steps are needed and these steps require the integration of the extracting solvent with the immunoassay. When solvent extraction is required, solvent effects on the assay are determined during assay optimization. Another option is to extract in the desired solvent, then conduct a solvent exchange into a more miscible solvent. Immunoassays perform best with water-miscible solvents when solvent concentrations are below 20%. Our experience has been that nearly every matrix requires a complete validation. Various soil types and even urine samples from different animals within a species may cause enough variation that validation in only a few samples is not sufficient. 

Data from chemical characterization were used to estimate possible adverse effects on humans and the environmental receptors. Following previously published works [11, 19], a hypothetic scenario was set up to assess the risk posed by these non-conventional matrix an accidental leachate release into ground-water resulting in 1 100 and 1 1,000 dilutions of the leachate compounds, which have been subjected to dilution as the leachate mixes with the groundwater (Fig. 3). 

Column studies employ the same general techniques as flask studies, except glass tubes are packed with aquifer matrix, and groundwater, with or without amendments, is percolated through the column. Sterile and nutrient-amended columns are used as controls. Leachate is tested to determine the rate and type of chemical change that occurs in the column. While column studies do not accurately reflect the actual subsurface environment, they do provide an indication of the likely effects of sorption and precipitation within the aquifer. 

The Lewis ENVIRO-CLEAN process removes and recovers metals such as chromium, copper, nickel, mercury, lead, zinc, iron, and cadmium and has effectively demonstrated that it can treat a matrix of multiple metals in a single stream with positive results. The process treats wastes from wood preserving, metal finishing, mining, surface and groundwaters. The two-step process uses granular-activated carbon and electrolytic metal recovery to yield a salable metallic by-product. 

It would lie far beyond the aim of this chapter to introduce the state-of-the art concepts that have been developed to quantify the influence of colloids on transport and reaction of chemicals in an aquifer. Instead, a few effects will be discussed on a purely qualitative level. In general, the presence of colloidal particles, like dissolved organic matter (DOM), enhances the transport of chemicals in groundwater. Figure 25.8 gives a conceptual view of the relevant interaction mechanisms of colloids in saturated porous media. A simple model consists of just three phases, the dissolved (aqueous) phase, the colloid (carrier) phase, and the solid matrix (stationary) phase. The distribution of a chemical between the phases can be, as first step, described by an equilibrium relation as introduced in Section 23.2 to discuss the effect of colloids on the fate of polychlorinated biphenyls (PCBs) in Lake Superior (see Table 23.5). 

Siegel M. D. and Erickson K. E. (1986) Geochemical sensitivity analysis for performance assessment of HEW repositories effects of speciation and matrix diffusion. Proceedings of the Symposium on Groundwater Flow and Transport Modeling for Performance Assessment of Deep Geologic Disposal of Radioactive Waste A Critical Evaluation of the State of the Art. Sandia National Eaboratories, Albuquerque, NM, pp. 465-488. 

If TPH is introduced at any depth within the soil matrix, as in the case of leaks from underground storage tanks, natural weather and biodegradation processes are rendered less effective and the chances are increased that some of the TPH fractions may contaminate groundwater. Since many... 

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