Chemical and Toxicological Effects on Cache Slough after Storm-Driven Contaminant Inputs

Chemical and toxicological testing in the Cache Slough complex (the slough) of the North Delta indicated the aquatic biota are exposed to a variety of wastewater-derived food additives, pharmaceuticals, and personal care products in highest concentration during dry periods, and many insecticides, herbicides and fungicides with peak concentrations after winter rains. The insecticide groups currently known to be of greatest toxicological concern are the pyrethroids and the fiproles (i.e., fipronil and its degradation products). After stormwater runoff enters the system via Ulatis Creek, both pesticide groups attained concentrations that posed a threat to aquatic life. When the commonly used testing species, Hyalella azteca, was placed in Cache Slough, toxicity — and, at times, near total mortality — was seen over at least an 8-km reach of Cache Slough that extended from the uppermost end almost to the junction with the Deep Water Ship Channel. Previous work over many years has shown similar results after other winter storms. However, when H. azteca that carried a mutation providing resistance to pyrethroid pesticides were also deployed in the slough, no ill effects were observed, which provided strong evidence that pyrethroids were responsible for toxicity to the non-resistant strain. Abundant resident H. azteca in Cache Slough carry any of four mutations that provide resistance to pyrethroids. They also carry a mutation that provides resistance to organophosphate pesticides, and likely carbamate pesticides as well. After many years of exposure, sensitive genotypes have been nearly eliminated from the system, and replaced by a population unaffected by many insecticides now in common use. We offer a variety of reasons why this shift to a population with mutant genotypes is of considerable concern, but also note that society has yet to fully consider the ecological and regulatory ramifications of the evolutionary attainment of pollutant resistance

Development and Application of Liquid Chromatographic Retention Time Indices in HRMS-Based Suspect and Nontarget Screening

There is an increasing need for comparable and harmonized retention times (tR) in liquid chromatography (LC) among different laboratories, to provide supplementary evidence for the identity of compounds in high-resolution mass spectrometry (HRMS)-based suspect and nontarget screening investigations. In this study, a rigorously tested, flexible, and less system-dependent unified retention time index (RTI) approach for LC is presented, based on the calibration of the elution pattern. Two sets of 18 calibrants were selected for each of ESI+ and ESI-based on the maximum overlap with the retention times and chemical similarity indices from a total set of 2123 compounds. The resulting calibration set, with RTI set to range between 1 and 1000, was proposed as the most appropriate RTI system after rigorous evaluation, coordinated by the NORMAN network. The validation of the proposed RTI system was done externally on different instrumentation and LC conditions. The RTI can also be used to check the reproducibility and quality of LC conditions. Two quantitative structure-retention relationship (QSRR)-based models were built based on the developed RTI systems, which assist in the removal of false-positive annotations. The applicability domains of the QSRR models allowed completing the identification process with higher confidence for substances within the domain, while indicating those substances for which results should be treated with caution. The proposed RTI system was used to improve confidence in suspect and nontarget screening and increase the comparability between laboratories as demonstrated for two examples. All RTI-related calculations can be performed online at http://rti.chem.uoa.gr/.

Using Mutations for Pesticide Resistance to Identify the Cause of Toxicity in Environmental Samples

Traditional Toxicity Identification Evaluations (TIE) are applied to identify causal agents in complex environmental samples showing toxicity and rely upon physical or chemical manipulation of samples. However, mutations conferring toxicant resistance provide the opportunity for a novel biologically based TIE. Populations within the <i>Hyalella azteca</i> complex from pesticide-affected waterways were 2 and 3 orders of magnitude more resistant to the pyrethroid cyfluthrin and the organophosphate chlorpyrifos, respectively, than laboratory-cultured <i>H. azteca</i> widely used for toxicity testing. Three resistant populations, as well as laboratory-cultured, nonresistant <i>H. azteca</i>, were exposed to urban and agricultural runoff. Every sample causing death or paralysis in the nonresistant individuals had no effect on pyrethroid-resistant individuals, providing strong evidence that a pyrethroid was the responsible toxicant. The lack of toxicity to chlorpyrifos-sensitive, but pyrethroid-resistant, individuals suggested chlorpyrifos was not a likely toxicant, a hypothesis supported by chemical analysis. Since these mutations that confer resistance to pesticides are highly specific, toxicity to wild-type, but not resistant animals, provides powerful evidence of causality. It may be possible to identify strains resistant to even a wider variety of toxicants, further extending the potential use of this biologically based TIE technique beyond the pyrethroid and organophosphate-resistant strains currently available

The strength in numbers: comprehensive characterization of house dust using complementary mass spectrometric techniques

Untargeted analysis of a composite house dust sample has been performed as part of a collaborative effort to evaluate the progress in the field of suspect and nontarget screening and build an extensive database of organic indoor environment contaminants. Twenty-one participants reported results that were curated by the organizers of the collaborative trial. In total, nearly 2350 compounds were identified (18%) or tentatively identified (25% at confidence level 2 and 58% at confidence level 3), making the collaborative trial a success. However, a relatively small share (37%) of all compounds were reported by more than one participant, which shows that there is plenty of room for improvement in the field of suspect and nontarget screening. An even a smaller share (5%) of the total number of compounds were detected using both liquid chromatography–mass spectrometry (LC-MS) and gas chromatography–mass spectrometry (GC-MS). Thus, the two MS techniques are highly complementary. Most of the compounds were detected using LC with electrospray ionization (ESI) MS and comprehensive 2D GC (GC×GC) with atmospheric pressure chemical ionization (APCI) and electron ionization (EI), respectively. Collectively, the three techniques accounted for more than 75% of the reported compounds. Glycols, pharmaceuticals, pesticides, and various biogenic compounds dominated among the compounds reported by LC-MS participants, while hydrocarbons, hydrocarbon derivatives, and chlorinated paraffins and chlorinated biphenyls were primarily reported by GC-MS participants. Plastics additives, flavor and fragrances, and personal care products were reported by both LC-MS and GC-MS participants. It was concluded that the use of multiple analytical techniques was required for a comprehensive characterization of house dust contaminants. Further, several recommendations are given for improved suspect and nontarget screening of house dust and other indoor environment samples, including the use of open-source data processing tools. One of the tools allowed provisional identification of almost 500 compounds that had not been reported by participants. [Figure not available: see fulltext.]. © 2019, The Author(s)