Challenges Associated with Generating Reliable Nanogram-per-Liter Measurements of Hexavalent Chromium in Groundwater.

The US Environmental Protection Agency (USEPA) and several states are considering regulatory limits for hexavalent chromium (Cr(VI)) <100 ng/L, increasing the importance of obtaining accurate and reliable data. The present study presents the results of 2 studies investigating the effectiveness of chemical preservation on ng/L concentrations of Cr(VI) in groundwater. Chemically preserved and unpreserved aliquots of a groundwater sample were spiked with a known amount of Cr(VI), and then analyzed in tandem with sets of preserved and unpreserved performance test samples over 28 d. The studies showed that although Cr(VI) appears to be relatively stable over 28 d, it may be sensitive to minor matrix changes after collection. The studies also demonstrated significant challenges to measuring Cr(VI) below 100 ng/L, because the results can be subject to positive bias or contamination that may not be readily apparent. We conclude that Cr(VI) measurements using a USEPA published method below 100 ng/L may be categorized as semiquantitative at best. Environ Toxicol Chem 2020;39:1526-1533. © 2020 SETAC.

Selenium bioaccumulation in fish exposed to coal ash at the Tennessee Valley Authority Kingston spill site.

In December 2008, 4.1 million cubic meters of coal ash were released into the Emory and Clinch Rivers by the Tennessee Valley Authority Kingston Fossil Plant. Coal ash contains several contaminants, including the bioaccumulative metalloid selenium (Se). Because Se is predominantly accumulated in aquatic organisms through dietary rather than aqueous exposure, tissue-based toxicity thresholds for Se are currently being considered. The proposed threshold concentrations range between 4 µg/g and 9 µg/g Se (dry wt.) in whole body fish, with a proposed fillet threshold of 11.8 µg/g. In the present study, the authors examined the spatial and temporal trends in Se bioaccumulation and examined the relationship between the Se content in fillets and in whole bodies of fish collected around the Kingston spill site to determine whether Se bioaccumulation was a significant concern at the ash spill site. Whereas Se concentrations in fish (whole bodies and fillets) were elevated at sampling locations affected by the Kingston ash spill relative to reference locations, concentrations do not appear to be above risk thresholds and have not been increasing over the 5-yr period since the spill. These findings are not only relevant to guiding the human health and ecological risk assessments at the Kingston ash spill site, but because of current national discussions on appropriate guidelines for Se in fish as well for the disposal of coal combustion wastes, the results are also relevant to the general understanding of Se bioaccumulation in contaminated water bodies.

Automated near-continuous glucose monitoring measured in plasma using mid-infrared spectroscopy.

OBJECTIVE: There are increasing calls for a precise, automated system to enable tight glycemic control and to avoid hypoglycemia in an intensive care unit setting. OptiScan Biomedical has developed a glucose monitor based on mid-infrared spectroscopy that withdraws blood samples (120 µl) and measures plasma glucose. The goal of this study was to validate the performance of the OptiScan Model 5000 over a wide range of glycemic levels in patients. RESEARCH DESIGN AND METHODS: Sixty people with type 1 (n = 18) or type 2 (n = 42) diabetes who were otherwise healthy were connected to OptiScanners. Their blood glucose concentrations were kept in a euglycemic, hypoglycemic (<75 mg/dl), and hyperglycemic (>180 mg/dl) range by intravenous administrations of insulin and glucose. OptiScanner venous blood samples were automatically withdrawn every 15 minutes. Reference measurements were done using the YSI 2300 glucose analyzer. RESULTS: The aggregate data points (1155 paired readings) were within International Organization for Standardization standards, with 98.6% of the glucose values within ±20% above 75 mg/dl and ±15 mg/dl below this value. A Clarke error grid analysis showed a total of 1139 points (98.6%) in zone A. Points outside of A exceeded the A zone boundary by an average of 4.3%. The r(2) was 0.99. The total coefficient for variance was 6.4%. CONCLUSIONS: These results show that the OptiScanner is highly accurate in healthy patients with diabetes across a wide range of glucose values. Mid-infrared spectroscopy may become the method of choice for highly accurate, high frequency, automated glucose measurements and may thus enable better glycemic control in critically ill patients.