Temporal patterns and sources of atmospherically deposited pesticides in Alpine Lakes of the Sierra Nevada, California, U.S.A

Agricultural pesticides are being transported by air large distances to remote mountain areas and have been implicated as a cause for recent population declines of several amphibian species in such locations. Largely unmeasured, however, are the magnitude and temporal variation of pesticide concentrations in these areas, and the relationship between pesticide use and pesticide appearance in the montane environment. We addressed these topics in the southern Sierra Nevada mountains, California, by sampling water weekly or monthly from four alpine lakes from mid-June to mid-October 2003. The lakes were 46-83 km from the nearest pesticide sources in the intensively cultivated San Joaquin Valley. Four of 41 target pesticide analytes were evaluated for temporal patterns: endosulfan, propargite, dacthal, and simazine. Concentrations were very low, approximately 1 ng/L or less, at all times. The temporal patterns in concentrations differed among the four pesticides, whereas the temporal pattern for each pesticide was similar among the four lakes. For the two pesticides applied abundantly in the San Joaquin Valley during the sampling period, endosulfan and propargite, temporal variation in concentrations corresponded strikingly with application rates in the Valley with lag times of 1-2 weeks. A finer-scale analysis suggests that a large fraction of these two pesticides reaching the lakes originated in localized upwind areas within the Valley.

Roxarsone and transformation products in chicken manure: Determination by capillary electrophoresis-inductively coupled plasma-mass spectrometry

The determination of the animal feed additive roxarsone (3-nitro-4-hydroxyphenylarsonic acid) and six of its possible transformation products (arsenite, arsenate, monomethylarsonate, dimethylarsinate, 3-amino-4-hydroxyphenylarsonic acid, and 4-hydroxyphenylarsonic acid) in chicken manure was investigated using capillary electrophoresis-inductively coupled plasma-mass spectrometry (CE-ICP-MS). Initial method development was conducted using ultraviolet (UV) detection for ruggedness and time efficiency. Separation of these seven arsenic species was effected using a 20 mM phosphate buffer at pH 5.7. The CE-ICP-MS limits of detection in terms of As for each of the species was in the low microg.L(-1) range, corresponding to absolute detection limits in the range 20-70 fg As (based on a 23 nL injection). Overall, the method developed in this study provides high selectivity and low limits of detection (1-3 microg.L(-1) or low-ppb, based on As), uses small sample volume (low nL), and produces minimal wastes.

Determination of arsenobetaine, arsenocholine, and tetramethylarsonium cations by liquid chromatography-thermochemical hydride generation-atomic absorption spectrometry

A novel high-performance liquid chromatography-atomic absorption spectrometry (HPLC-AAS) interface based on thermochemical hydride generation has been developed and optimized for the determination of arsenobetaine [(CH3)3As+CH2COOH], arsenocholine [(CH3)3As+CH2CH2OH], and tetramethylarsonium [(CH3)4As+] cations. In this quartz interface, the methanolic HPLC eluent was nebulized by thermospray effect and pyrolyzed in a methanol/oxygen kinetic flame and the analytes were thermochemically derivatized to the hydride derivative in the presence of excess hydrogen. The volatile derivative was then transported to a cool diffusion H2/O2 flame atomizer. The fact that arsenic pentoxide was also derivatized, and that no signal was observed in the absence of postthermospray hydrogen or the absence of cool diffusion flame, corroborated the thermochemically mediated arsine-generation mechanism. Factorial models predicting the performance of the interface at different levels of five selected variables suggested that (a) both reverse- and normal-phase HPLC eluents were compatible with the interface and (b) the performance of this system was relatively insensitive (less than 50% variation in response) to changes over wide ranges in the operating parameters. At concentrations up to 10-fold excess, potential interferents [(CH3)3S+, (CH3)3Pb+] did not affect, significantly, the postulated thermochemical hydride generation (THG) process. However, a 10-fold molar excess of (CH3)3Se+ decreased the response of the analyte by 48%. Virtually identical responses were observed for equimolar amounts of tetramethylarsonium, arsenocholine, arsenobetaine [As(-III)], and dimethylarsinic acid [As(III)]. Arsenic pentoxide [As(V)] was detected with 75% efficiency, relative to the response of the organoarsenic compounds.(ABSTRACT TRUNCATED AT 250 WORDS)