Water samples Weathering

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

Microorganisms readily able to degrade hydrocarbons were found in the Neuse River estuary in North Carolina. Although the estuary was relatively free of hydrocarbon contamination, 63% of the bacteria and 71% of the fungi isolated from surface water samples were able to utilize kerosene as the sole carbon source (Buckley et al. 1976). Weathered kerosene (volatile components were allowed to escape prior to testing) was spiked with four marker hydrocarbons, and the degradation of the markers was monitored. 

Observations (presence of sheen on the sampled water unusual sampling point or sample appearance the formation of effervescence in preserved water samples change in weather conditions etc.)... 

Figure 10. Fractionation of natural water sampled in dry weather conditions (left) and under rain conditions (right) [18].

Figure 10 presents the fractionation of natural water sampled during dry weather and wet weather [18],... 

During wet weather, the river water sample contains a TSS concentration of 276 mg/L (measured by a reference method), principally of mineral composition as organic fraction represents only 18%. The size distribution of solids, put in suspension in water by rain flow, is very wide. Settleable, supracolloidal and colloidal solids are present in water. Several filtration steps have been carried out, and the corresponding UV spectra of the... 

Jones et al. (1967) first reported that the average 8 Sj./86Sr ratio of 15 water samples from a depth profile of Lake Vanda is 0.7149 0.0(X)1 which is identical within analytical error to the Sr/ Sr ratio of 0.7146 0.0002 of strontium in the water of the Onyx River. On the other hand, the Sr/ Sr ratios of strontium in Lake Vanda and the Onyx River differ markedly from the average Sr/ Sr ratio of the Cenozoic basalt of the McMurdo Volcanics (0.7043) and from the average Sr/ Sr ratio of two samples of seawater from the Ross Sea (0.7094). These results indicate unequivocally that the strontium at all levels in Lake Vanda and in Onyx River did not originate from marine sources or by weathering of Cenozoic basalt or volcanic ash in Wright Valley. 

Phosphate. Phosphoms occurs in water primarily as a result of natural weathering, municipal sewage, and agricultural mnoff The most common form in water is the phosphate ion. A sample containing phosphate can react with ammonium molybdate to form molybdophosphoric acid (H2P(Mo202q)4). This compound is reduced with stannous chloride in sulfuric acid to form a colored molybdenum-blue complex, which can be measured colorimetrically. SiUca and arsenic are the chief interferences. 

Thorinm-232 is the only non-radiogenic thorium isotope of the U/Th decay series. Thorinm-232 enters the ocean by continental weathering and is mostly in the particulate form. Early measurements of Th were by alpha-spectrometry and required large volume samples ca. 1000 T). Not only did this make sample collection difficult, but the signal-to-noise ratio was often low and uncertain. With the development of a neutron activation analysis " and amass spectrometry method " the quality of the data greatly improved, and the required volume for mass spectrometry was reduced to less than a liter. Surface ocean waters typically have elevated concentrations of dissolved and particulate 17,3 7,62... 

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