Biomedical subjects

Ying D Lei

Publications and source records attributed to Ying D Lei.

4 recordsLinked to original sources

PubMed2006

Polychlorinated biphenyls and polybrominated diphenyl ethers in the North American atmosphere.

To assess the spatial concentration variability of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the atmosphere on a large continental scale, their annually integrated air concentrations were determined in 2000/2001 using XAD-based passive air samplers (PAS). The network included 40 stations in Canada, the United States, Mexico, Belize and Costa Rica, and covered 72 degrees of latitude and longitude. Total concentrations of PCB and PBDE congeners ranged from below the detection limit to 130 ng PAS-1 and 24 ng PAS-1, respectively. PCBs displayed a large variation between urban, rural and remote sites, whereas PBDEs did not follow such a pattern. Open burning of "Penta"-containing waste may have contributed to the PBDEs detected in the air samples from rural and remote areas. Air from the Canadian Arctic had a relatively higher percentage of lighter PCB congeners than air sampled in the tropical region, which is interpreted as evidence for global fractionation.

Air Pollutants↗

PubMed2006

Comparative evaluation of three high-performance liquid chromatography-based Kow estimation methods for highly hydrophobic organic compounds: polybrominated diphenyl ethers and hexabromocyclododecane.

Three methods for estimating the octanol-water partition coefficient (Kow) based on its relationship with capacity factors on reversed-phase (RP) high-performance liquid chromatography (HPLC) columns were compared in terms of their applicability to highly hydrophobic compounds (HHCs). Methods based on simple isocratic elutions were found to be unsuitable, because the very high organic modifier fractions that are required to elute HHCs from RP columns challenge the basic assumption of the similarity between the octanol-water and RP-eluent systems. Compound planarity was found to exert a considerable influence on the retention of HHCs in RP columns, leading to different linear calibration curves for chlorobenzenes and chlorobiphenyls. Only an empirical exponential regression succeeded in describing the behavior of both groups of compounds during gradient elutions. In a method based on isocratic retention times at multiple temperatures, satisfactory calibration was achieved with a multivariate linear regression that included a numerical indicator of compound planarity. Considering experimental simplicity, speed, precision, and accuracy, with the latter judged by comparison with Kow values for polybrominated diphenyl ethers and polychlorinated naphthalenes as reported in the literature, a gradient elution combined with an exponential calibration curve is recommended for estimating the Kow of HHCs. To our knowledge, the first isomer-specific Kow values for hexabromocyclododecane are reported. Bearing in mind that the influence of structural characteristics on retention is likely to increase with hydrophobicity, it is not justified to judge a HPLC-based Kow estimation method as being suitable for HHCs because it is shown to work well for less hydrophobic substances. Whereas univariate linear regressions often may prove to be sufficient when dealing with substances having a log Kow, of less than five, methods for HHCs need to account for the influence of structure on retention.

Chromatography, High Pressure Liquid↗

PubMed2005

Atmospheric distribution and long-range transport behavior of organochlorine pesticides in North America.

Annually averaged concentrations and enantiomeric compositions of organochlorine pesticides (OCPs) in air were determined in 2000/2001 at 40 stations across North America using XAD-based passive samplers. Absolute concentration differences acrossthe continent, the skewness and kurtosis of the concentration distribution, the relative abundance of parent compound and metabolites, and the chiral signatures can identify regional sources of OCP to the atmosphere. Specifically, air samples collected in the southeastern United States had elevated concentrations of chlordane-related compounds, higher ratios of trans- to cis-chlordane and heptachlor to heptachlor epoxide, as well as higher enantiomeric fractions of trans-chlordane as compared to other regions, suggesting continued release of microbially unprocessed chlordane to the regional atmosphere. Similarly, greatly elevated concentrations of p,p'-DDT, low relative abundance of the metabolite DDE, and a racemic composition of o,p'-DDT in samples from southern Mexico and Belize indicate recent use of DDT in these regions. Belize is also a potential source region for dieldrin. Reflecting its continued use in North America, endosulfan is now one of the most abundant and ubiquitous OCPs in the continental atmosphere. In contrast to these OCPs, air concentrations of penta- and hexachlorobenzene vary only by factors of 2-4 across the continent, reflecting a long atmospheric residence time and few primary sources. Atmospheric levels of the chlorobenzenes, alpha-endosulfan, and p,p'-DDE increase with elevation in the Canadian Rocky Mountains. Empirical travel distances for the OCPs derived from latitudinal concentration profiles are in good agreementwith model-derived indicators of long-range transport potential and, in particular, lead to a similar categorization of the OCPs. Large-scale passive air sampling networks are suitable for monitoring compliance with, and effectiveness of, regulatory control measures and for establishing experimentally the atmospheric long-range transport behavior of organic air pollutants.

Air Movements↗

PubMed2004

Hexachlorocyclohexanes in the North American atmosphere.

Annually integrated air concentrations of alpha- and gamma-hexachlorocyclohexane (HCH) were determined in 2000/2001 at 40 stations across North America using XAD-based passive air samplers to understand atmospheric distribution processes on a continental scale. Elevated levels of gamma-HCH in the atmosphere of the Canadian Prairies are consistent with the ongoing use of lindane as a seed treatment on canola and confirm the feasibility of detecting the agricultural use of a pesticide using long-term integrated passive air sampling. In contrast to gamma-HCH, the atmospheric concentrations of alpha-HCH show a rather uniform distribution across Canada and the United States, which is expected for a chemical with no current use on the continent. Higher levels in the atmosphere over Atlantic Canada can be explained by alpha-HCH evaporating from the waters of the Labrador Current, which is supported bythe chiral composition of alpha-HCH and the temperature dependence of its atmospheric concentrations along the east coast of Canada. Similarly, alpha-HCH is volatilizing from Lake Superior. Atmospheric HCH levels increase with elevation in the Canadian Rocky Mountains. The results suggest that evaporation, in particular from cold water bodies, is an important source of alpha-HCH to the North American atmosphere. Low levels of HCHs in Central America hint at efficient degradation under tropical conditions. Chiral analysis shows that (+)-alpha-HCH is often enriched in air over continental areas and at the Pacific Coast, which is opposite to the enantiomeric enrichment in the proximity to the Great Lakes and the Atlantic Ocean. Passive air sampling is a powerful tool to discern the large-scale variability of semivolatile and persistent organic chemicals in the atmosphere.

Agriculture↗