A Decade of Global Atmospheric Monitoring Delivers Mixed Report Card on the Stockholm Convention.

Time trends in atmospheric concentrations serve to evaluate how effective the Stockholm Convention is in reducing or eliminating environmental releases of persistent organic pollutants (POPs). Twelve years (2005-2016) of continuous monitoring with a global network of 20 sampling sites reveals that concentrations of the pesticide endosulfan began to drop coincident with its listing as POP in 2011. Concentrations of other POPs started to decrease prior to listing and during the sampling period declined very slowly or not at all. Concentrations of some unintentionally produced POPs (hexachlorobenzene, hexachlorobutadiene) increased to become the most abundant and most widely dispersed POPs in the global atmosphere. Their formation processes and release locations need to be identified to facilitate the Convention's goal of curbing releases from unintentional production.

Contaminant Biomagnification in Polar Bears: Interindividual Differences, Dietary Intake Rate, and the Gut Microbiome.

Some persistent hydrophobic pollutants biomagnify, i.e., achieve higher contaminant levels in a predator than in its prey (Cpredator/Cprey > 1). This ratio is called the biomagnification factor (BMF) and is traditionally determined using tissues from carcasses or biopsies. Using a noninvasive method that relies on equilibrium sampling in silicone-film-coated vessels and chemical analysis of paired diet and feces, we determined on three occasions the thermodynamic biomagnification limit (BMFlim) and feces-based biomagnification factor (BMFF) for three zoo-housed polar bears who experience seasonal periods of hyperphagia and hypophagia. All bears had high biomagnification capabilities (BMFlim was up to 200) owing to very efficient lipid assimilation (up to 99.5%). The bears differed up to a factor of 3 in their BMFlim. BMFlim and BMFF of a bear increased by up to a factor of 4 during the hypophagic period, when the ingestion rate was greatly reduced. Much of that variability can be explained by differences in the lipid assimilation efficiency, even though this efficiency ranged only from 98.1 to 99.5%. A high BMFlim was associated with a high abundance of Bacteroidales and Lachnospirales in the gut microbiome. Biomagnification varies to a surprisingly large extent between individuals and within the same individual over time. Future work should investigate whether this can be attributed to the influence of the gut microbiome on lipid assimilation by studying more individual bears at different key physiological stages.

Sources and environmental fate of halomethoxybenzenes.

Halomethoxybenzenes are pervasive in the atmosphere at concentration levels that exceed, often by an order of magnitude, those of the persistent organic pollutants with which they share the attributes of persistence and potential for long-range transport, bioaccumulation, and toxic effects. Long ignored by environmental chemists because of their predominantly natural origin-namely, synthesis by terrestrial wood-rotting fungi, marine algae, and invertebrates-knowledge of their environmental pathways remains limited. Through measuring the spatial and seasonal variability of four halomethoxybenzenes in air and precipitation and performing complementary environmental fate simulations, we present evidence that these compounds undergo continental-scale transport in the atmosphere, which they enter largely by evaporation from water. This also applies to halomethoxybenzenes originating in terrestrial environments, such as drosophilin A methyl ether, which reach aquatic environments with runoff, possibly in the form of their phenolic precursors. Our findings contribute substantially to the comprehension of sources and fate of halomethoxybenzenes, illuminating their widespread atmospheric dispersal.

Dry eye disease due to meibomian gland dysfunction treated with Pinggan Yuyin Qingre formula: a stratified randomized controlled trial.

OBJECTIVE: To observe the clinical efficacy on improving the quality of meibum in patients suffer from dry eye disease (DED) due to meibomian gland dysfunction (MGD) with hyperactivity ofdue todeficiency pattern after being treated with Pinggan Yuyin Qingre formula (, PGYYQR). METHODS: Totally 120 patients who met the inclusion criteria were included and stratified into three levels according to the level of MGD (1-3), and patients in each level was randomly allocated into the treatment group and control group according to a 1∶1 ratio. Both groups were treated with sodium hyaluronate eye drops, and the treatment group was also given PGYYQR granules. Both groups were treated continuously for eight weeks. The score of the properties of meibomian gland (MG) secretion, the score of the palpebral margins, the average noninvasive tear breakup time (NITBUTav), lipid layer thickness (LLT), and Traditional Chinese Medicine (TCM) syndrome efficacy were compared between the two groups after treatment. RESULTS: A total of 116 cases were included in the statistical analysis. The differences were statistically significant in the score of the properties of MG secretion, the score of the palpebral margins, and NITBUTav between the two groups after treatment, the treatment group was superior to the control group; there was no evidence of a difference in LLT. In terms of TCM syndrome efficacy, the total effective rate was 84.7% in the treatment group and 50.9% in the control group, with the statistically significant difference. None of the included cases had adverse reactions. CONCLUSIONS: PGYYQR is effective in improving the quality of meibum, and the tear film stability which thereby relieving the ocular symptoms in MGD-related DED patients with hyperactivity ofdue todeficiency pattern.

Field Calibration and PAS-SIM Model Evaluation of the XAD-Based Passive Air Sampler for Semi-Volatile Organic Compounds.

The use of passive air samplers (PAS) for semi-volatile organic compounds (SVOCs) continues to expand. To advance quantitative understanding of uptake kinetics, we calibrated the XAD-PAS, using a styrene-divinylbenzene sorbent, through a year-long side-by-side deployment with an active sampler. Twelve XAD-PASs, deployed in June 2020, were retrieved at 4-week intervals, while gas phase SVOCs were quantified in 48 consecutive week-long active samples taken from June 2020 to May 2021. Consistent with XAD's high uptake capacity, even relatively volatile SVOCs, such as hexachlorobutadiene, displayed linear uptake throughout the entire deployment. Sampling rates (SRs) range between 0.1 and 0.6 m3 day-1 for 26 SVOCs, including brominated flame retardants, organophosphate esters, and halogenated methoxylated benzenes. SRs are compared with experimental SRs reported previously. The ability of the existing mechanistic uptake model PAS-SIM to reproduce the observed uptake and SRs was evaluated. Agreement between simulated and measured uptake curves was reasonable but varied with compound volatility and the assumed stagnant air layer boundary thickness. Even though PAS-SIM succeeds in predicting the SR range for the studied SVOCs, it fails to capture the volatility dependence of the SR by underestimating the length of the linear uptake period and by failing to consider the kinetics of sorption.

Seasonal and latitudinal variability in the atmospheric concentrations of cyclic volatile methyl siloxanes in the Northern Hemisphere.

Field data from two latitudinal transects in Europe and Canada were gathered to better characterize the atmospheric fate of three cyclic methylsiloxanes (cVMSs), i.e., octamethyl-cyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6). During a year-long, seasonally resolved outdoor air sampling campaign, passive samplers with an ultra-clean sorbent were deployed at 15 sampling sites covering latitudes ranging from the source regions (43.7-50.7 °N) to the Arctic (79-82.5 °N). For each site, one of two passive samplers and one of two field blanks were separately extracted and analyzed for the cVMSs at two different laboratories using gas-chromatography-mass spectrometry. Whereas the use of a particular batch of sorbent and the applied cleaning procedure to a large extent controlled the levels of cVMS in field blanks, and therefore also the method detection and quantification limits, minor site-specific differences in field blank contamination were apparent. Excellent agreement between duplicates was obtained, with 95% of the concentrations reported by the two laboratories falling within a factor of 1.6 of each other. Nearly all data show a monotonic relationship between the concentration and distance from the major source regions. Concentrations in source regions were comparatively constant throughout the year, while the concentration gradient towards remote regions became steeper during summer when removal via OH radicals is at its maximum. Concentrations of the different cVMS oligomers were highly correlated within a given transect. Changes in relative abundance of cVMS oligomers along the transect were in agreement with relative atmospheric degradation rates via OH radicals.

Probing the Thermodynamics of Biomagnification in Zoo-Housed Polar Bears by Equilibrium Sampling of Dietary and Fecal Samples.

In a proof-of-concept study, we recently used equilibrium sampling with silicone films to noninvasively derive the thermodynamic limit to a canine's gastrointestinal biomagnification capability (BMFlim) by determining the ratio of the products of the volume (V) and fugacity capacity (Z) of food and feces. In that earlier study, low contaminant levels prevented the determination of contaminant fugacities (f) in food and feces. For zoo-housed polar bears, fed on a lipid-rich diet of fish and seal oil, we were now able to measure the increase in f of nine native polychlorinated biphenyls (PCBs) upon digestion, providing incontestable proof of the process of gastrointestinal biomagnification. A high average BMFlim value of ∼171 for the bears was caused mostly by a remarkable reduction in fugacity capacity driven by a high lipid assimilation capacity. Lipid-rich diets increase the uptake of biomagnifying contaminants in two ways: because they tend to have higher contaminant concentrations and because they lead to a high Z value drop during digestion. We also confirmed that equilibrium sampling yielded similar Z values for PCBs originally present in food and feces and for isotopically labeled PCBs spiked onto those samples, which makes the method suitable for investigating the biomagnification capability of organisms, even if native contaminant concentrations in their diet and feces are low.

Identifying organic chemicals not subject to bioaccumulation in air-breathing organisms using predicted partitioning and biotransformation properties.

Because the respiration processes contributing to the elimination of organic chemicals deviate between air- and water-breathing organisms, existing and widely used procedures for identifying chemicals not subject to bioaccumulation in aquatic organisms based on the octanol-water partition ratio KOW need to be complemented with similar procedures for organisms respiring air. Here, we propose such a procedure that relies on the comparison of a compound's predicted KOW , octanol-air partition ratio KOA , and biotransformation half-life HLB with three threshold values, below which elimination is judged to be sufficiently rapid to prevent bioaccumulation. The method allows for the consideration of the effect of dissociation on the efficiency of urinary and respiratory elimination. Explicit application of different types of the prediction error, such as the 95% prediction interval or the standard error, allows for variable tolerance for false-negative decisions, that is, the potential to judge a chemical as not bioaccumulative even though it is. A test with a set of more than 1000 diverse organic chemicals confirms the applicability of the prediction methods for a wide range of compounds and the procedure's ability to categorize approximately four-fifth of compounds as being of no bioaccumulation concern, suggesting its usefulness to screen large numbers of commercial chemicals to identify those worthy of further scrutiny. The test also demonstrates that a screening based solely on KOW and KOA would be far less effective because the fraction of chemicals that can be judged as sufficiently volatile and/or sufficiently water soluble for rapid respiratory and urinary elimination based on the partitioning properties predicted for their neutral form is relatively small. Future improvements of the proposed procedure depend largely on the development of prediction methods for the biotransformation kinetics in air-breathing organisms and for the potential for renal reabsorption. Integr Environ Assess Manag 2022;18:1297-1312. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Dose-response relationship of blood flow restriction training on isometric muscle strength, maximum strength and lower limb extensor strength: A meta-analysis.

Objective: To perform a meta-analysis on the efficacy and dose-response relationship of blood flow restriction training on muscle strength reported worldwide. Methods: Thirty-four eligible articles with a total sample size of 549 participants were included in the meta-analysis. This study was performed using the method recommended by the Cochrane Handbook (https://training.cochrane.org/handbook), and the effect size was estimated using the standardized mean difference (SMD) and using RevMan 5.3 software (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, 2014). Results: The meta-analysis showed that blood flow restriction training increased the lower limb extensor muscle strength [SMD = 0.72, 95%; confidence interval (CI): 0.43 to 1.00, p < 0.01], knee extensor isokinetic torque SMD = 0.48 [95% CI: 0.24 to 0.73, p < 0.01], knee flexor isokinetic torque SMD = 0.39 [95% CI: 0.11 to 0.67, p < 0.01], and squat one-repetition maximum [SMD = 0.28, 95% CI: 0.01 to 0.55, p < 0.01]. There was no publication bias. Evaluation of dose-response relationship showed that the training load, mode, frequency, duration, and maximum cuff pressure affected the muscle function. Conclusion: blood flow restriction training. 16 significantly improved lower limb muscle strength, and the optimal training conditions consisted of a weight load smaller or equal to 30% of one-repetition maximum, training duration longer than 4 weeks, frequency of more than 3 times/week, and maximum cuff pressure lower than 200 mmHg. Systematic Review Registration: website, identifier registration number.

Reliable Prediction of the Octanol-Air Partition Ratio.

The octanol-air equilibrium partition ratio (KOA ) is frequently used to describe the volatility of organic chemicals, whereby n-octanol serves as a substitute for a variety of organic phases ranging from organic matter in atmospheric particles and soils, to biological tissues such as plant foliage, fat, blood, and milk, and to polymeric sorbents. Because measured KOA values exist for just over 500 compounds, most of which are nonpolar halogenated aromatics, there is a need for tools that can reliably predict this parameter for a wide range of organic molecules, ideally at different temperatures. The ability of five techniques, specifically polyparameter linear free energy relationships (ppLFERs) with either experimental or predicted solute descriptors, EPISuite's KOAWIN, COSMOtherm, and OPERA, to predict the KOA of organic substances, either at 25 °C or at any temperature, was assessed by comparison with all KOA values measured to date. In addition, three different ppLFER equations for KOA were evaluated, and a new modified equation is proposed. A technique's performance was quantified with the mean absolute error (MAE), the root mean square error (RMSE), and the estimated uncertainty of future predicted values, that is, the prediction interval. We also considered each model's applicability domain and accessibility. With an RMSE of 0.37 and a MAE of 0.23 for predictions of log KOA at 25 °C and RMSE of 0.32 and MAE of 0.21 for predictions made at any temperature, the ppLFER equation using experimental solute descriptors predicted the KOA the best. Even if solute descriptors must be predicted in the absence of experimental values, ppLFERs are the preferred method, also because they are easy to use and freely available. Environ Toxicol Chem 2021;40:3166-3180. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Phase partitioning, transport and sources of Benzotriazole Ultraviolet Stabilizers during a runoff event.

Benzotriazole Ultraviolet Stabilizers (BT-UVs) are ubiquitous in the environment, given their wide use as additives in consumer products. Their bio-accumulative and toxic properties are increasingly being scrutinised, evinced by the recent proposition to add UV328 to the Stockholm Convention on Persistent Organic Pollutants. Here, we measured concentrations of six BT-UVs in the dissolved and particulate phases of stream water collected from an urban and rural stream during a runoff event. Under baseflow conditions, the less hydrophobic BT-UVs were present at low concentrations in the dissolved phase, while much higher loads of particulate BT-UVs occurred during stormflow, especially in the urban creek. Time-weighted average BT-UV concentrations were up to 4 times higher in the urban than in the rural creek. BT-UVs were found to be prevalent in water obtained from laundering textiles, which plausibly constitutes a major portion of domestic wastewater, and can serve as a BT-UV source to aquatic waterways. However, the observed dilution of a sewage tracer during the run-off event suggests that unregulated wastewater seepage is not responsible for the high BT-UV loads in storm water. High levels of UV328 and UV234 were detected in a select few plastic debris items collected from the urban watershed and in artificial turf grass, respectively. Whereas this may allow for the leaching of those BT-UVs into the creek, most plastic debris is more likely a sink than a source of BT-UVs. The observed input of particle-bound BT-UVs at the onset of the rain event indicates that most of the BT-UVs reach the creek with contaminated particles that had built up on surfaces during the antecedent dry period. UV328 was the dominant BT-UV in those particles. If such particle build-up occurs on road surfaces, it may suggest that the use of UV328 in automotive applications contributes to their presence in urban storm water.

Characterization of inhalation exposure to gaseous elemental mercury during artisanal gold mining and e-waste recycling through combined stationary and personal passive sampling.

While occupational inhalation exposure to gaseous elemental mercury (GEM) has decreased in many workplaces as mercury is being removed from most products and processes, it continues to be a concern for those engaged in artisanal and small-scale gold mining or in recycling mercury-containing products. Recently, stationary and personal passive air samplers based on activated carbon sorbents and radial diffusive barriers have been shown to be suitable for measuring GEM concentrations across the range relevant for chronic health effects. Here, we used a combination of stationary and personal passive samplers to characterize the inhalation exposure to GEM of individuals living and working in two Ghanaian gold mining communities and working at a Norwegian e-waste recycling facility. Exposure concentrations ranging from <7 ng m-3 to >500 µg m-3 were observed, with the higher end of the range occurring in one gold mining community. Large differences in the GEM exposure averaged over the length of a workday between individuals can be rationalized by their activity and proximity to mercury sources. In each of the three settings, the measured exposure of the highest exposed individuals exceeded the highest concentration recorded with a stationary sampler, presumably because those individuals were engaged in an activity that generated or involved GEM vapors. High day-to-day variability in exposure for those who participated on more than one day, suggests the need for sampling over multiple days for reliable exposure characterization. Overall, a combination of personal and stationary passive sampling is a cost-effective approach that cannot only provide information on exposure levels relative to regulatory thresholds, but also can identify emission hotspots and therefore guide mitigation measures.

Development, characterization, and testing of a personal passive sampler for measuring inhalation exposure to gaseous elemental mercury.

Inhalation of gaseous elemental mercury (GEM) is an occupational exposure concern for workers handling elemental mercury or mercury-containing waste. GEM is also often present near historically mercury-contaminated sites, potentially resulting in low-level, chronic exposure of the wider population. Here we introduce a passive sampler for personal GEM monitoring which combines a radial porous diffusive barrier with an activated carbon sorbent. A total mercury analyzer is used to quantify GEM sorbed to the carbon by thermal decomposition, amalgamation, and atomic absorption spectroscopy. A sampling rate of 0.070 m3/day was determined by calibrating the sampler at low and high concentrations. Deployments lasting 8 h result in limits of quantification well below 200 ng/m3. The sampler has a measurement range of at least four orders of magnitude. Derived air concentrations were not statistically significantly different from those obtained by active air sampling but were more precise than those obtained using a personal pump. If properly stored, the sampler maintains low blank levels in high GEM environments. Affordability, sturdiness, simplicity, and the wide availability of total mercury analyzers make this sampler highly suited for monitoring GEM inhalation exposure, including in developing countries.

Quantifying the Biomagnification Capability of Arctic Wolf and Domestic Dog by Equilibrium Sampling.

The mechanism underlying contaminant biomagnification is a decrease in the volume (V) and the fugacity capacity (Z) of food during digestion in the gastrointestinal tract. Traditionally, biomagnification is quantified by measuring contaminant concentrations in animal tissues. Here, we present a proof-of-concept study to noninvasively derive the thermodynamic limit to an organism's biomagnification capability (biomagnification limit -BMFlim) by determining the ratio of the V·Z-products of undigested and digested food. We quantify Z-values by equilibrating food and feces samples, which have been homogenized and spiked with polychlorinated biphenyls (PCBs), with silicone films of variable thickness coated on the inside of glass vials. We demonstrate the feasibility of this method for wolf (Canis lupus hudsonicus) and domestic dog (Canis lupus familiaris). For an adult wolf eating a relatively lean meat diet, a BMFlim (averaged over several PCB congeners) of approximately 41 was observed, whereas the BMFlim reached 81 for an adult domestic dog eating a lipid-rich diet. Besides the dietary lipid content that strongly affects the Z-value of the diet, the capability of an animal to digest its diet also influences the BMFlim by controlling the Z-values of their feces and the volume reduction of the food in the gastrointestinal tract. Less efficient digestion leads to a lower BMFlim in a juvenile dog (approximately 35) compared to its older self, even though their diets had similar lipid contents. The effect of the volume reduction (VD/VF ranging from 4 to 15) was comparable to the effect of the Z-value reduction (ZD/ZF from 3 to 20).

Comparing winter-time herbicide behavior and exports in urban, rural, and mixed-use watersheds.

The presence of pesticides in streams in winter, five to six years following bans on their municipal use suggests that complicated transport behaviour, such as subsurface retention and/or accumulation of pesticides and its release during storms, could be important for understanding recovery time frames following bans or legislation that aim to reduce chemical inputs. We investigated late fall and winter dynamics of four herbicides in paired urban and rural watersheds in Toronto, Canada during rainfall and snowmelt. The range of average concentrations and loads of the sum of atrazine, metolachlor, 2,4-D and mecoprop overlapped in the two types of watersheds, with slightly higher average concentrations in the rural watershed. Relatively consistent herbicide concentration-discharge patterns (i.e. dilution) were observed in the urban sub-watersheds during rainfall, while concentration-discharge patterns were much more variable in the rural watershed. This suggests relatively uniform transport pathways across the urban sub-watersheds, compared to the rural watershed. Concentration-discharge patterns of the neutral herbicides atrazine and metolachlor were similar in both watersheds during snowmelt, though varying discharge patterns resulted in divergent timings of peak concentrations. In contrast, the acidic pesticides 2,4-D and mecoprop, which are primarily associated with urban uses, showed much more variable behavior across both watersheds and merit further investigation. Overall, this work highlights the need to consider pesticide dynamics throughout the year in order to more thoroughly assess the long-term efficacy of legislation governing their use.

Investigating the Sources and Transport of Benzotriazole UV Stabilizers during Rainfall and Snowmelt across an Urbanization Gradient.

Benzotriazole UV stabilizers (BT-UVs) have attracted increasing attention due to their bioaccumulative nature and ubiquitous presence in surface waters. We apply high-frequency sampling in paired watersheds to describe, for the first time, the behavior of BT-UVs in stream channels during snowmelt and rainfall. Relative to a largely agricultural watershed, concentrations of BT-UVs in an urban watershed were 4-90 times greater during rainfall and 3-21 times greater during snowmelt. During rainfall, a decrease in BT-UV concentrations on particles with increasing suspended sediments and streamflow occurred at all urban sites due to input of relatively clean sediments, while both decreases and increases were observed at rural sites. Where increases occurred in the rural watershed, road sediments were consistently suggested as the source. Contrasts between the urban and rural sites were also observed during snowmelt. While BT-UV concentrations on particles peaked with peak suspended sediment levels at urban stream sites, the opposite was true at rural stream sites. This appeared to be driven partially by different snowpack melt rates in the two watersheds, with earlier melt and presumably higher streamflow facilitating suspension or erosion of more contaminated sediment in the urban stream. In general, it appears that relatively high, consistent emissions in the form of informal (plastic) debris disposal by consumers or industrial releases have likely led to more homogeneous BT-UV profiles and temporal behavior in the urban watershed. In the rural watershed, low emissions instead entail that emissions variability is more likely to translate to variability in chemical profiles and temporal behavior.

The transport of polycyclic aromatic hydrocarbons during rainfall and snowmelt in contrasting landscapes.

Though it has been established that stream concentrations of polycyclic aromatic hydrocarbons (PAHs) in urban watersheds can be much greater than those in less developed watersheds, knowledge of transport mechanisms is lacking, particularly in temperate, Northern climates with seasonal snow packs. We combine high-resolution stream water sampling with air, suspended solid and stream flow monitoring to investigate the source to stream transport of PAHs during rainfall and snowmelt in paired watersheds with contrasting land use. Despite similar particle loads, contamination of particles that is 8-48 times higher in the urban watersheds leads to area-normalized loads of PAHs that are 6-82 times greater than in the agricultural watersheds. In the urban watershed, average volumetric storm flow concentrations increase with longer antecedent dry period that allows build-up of PAHs on watershed surfaces. Cluster analysis suggests road dust is a minor source of suspended solid-bound PAHs in more agricultural watersheds during rainfall. During snowmelt, earlier peaks in concentration in the urban watershed are likely due to melt from snow packs and snow banks travelling quickly to the stream network via impervious surfaces and sewer drains. While road-derived inputs also appear to be important during snowmelt in the agricultural watershed, relatively delayed peak concentrations result from delayed inputs from snow packs in more pervious areas of the watershed.

Assessing the Source-to-Stream Transport of Benzotriazoles during Rainfall and Snowmelt in Urban and Agricultural Watersheds.

While benzotriazoles (BTs) are ubiquitous in urban waters, their sources and transport remain poorly characterized. We aimed to elucidate the origin and hydrological pathways of BTs in Toronto, Canada, by quantifying three BTs, electrical conductivity, and δ18O in high-frequency streamwater samples taken during two rainfall and one snowmelt event in two watersheds with contrasting levels of urbanization. Average concentrations of total BTs (∑BT) were 1.3 to 110 times higher in the more urbanized Mimico Creek watershed relative to the primarily agricultural and suburban Little Rouge Creek. Strong correlations between upstream density of major roads and total BT concentrations or BT composition within all events implicate vehicle fluids as the key source of BTs in both watersheds. Sustained historical releases of BTs within the Mimico Creek watershed have likely led to elevated ∑BT in groundwater, with elevated concentrations observed during baseflow that are diluted by rainfall and surface runoff. In contrast, relatively constant concentrations, caused by mixing of equally contaminated baseflow and rainfall/surface runoff, are observed in the Little Rouge Creek throughout storm hydrographs, with an occasional first flush occurring at a subsite draining suburban land. During snowmelt, buildup of BTs in roadside snowpiles and preferential partitioning of BTs to the liquid phase of a melting snowpack leads to early peaks in ∑BT in both streams, except the sites in the Little Rouge Creek with low levels of vehicle traffic. Overall, a history of BT release and land use associated with urbanization have led to higher levels of BTs in urban areas and provide a glimpse into future BT dynamics in mixed use, (sub)urbanizing areas.

Effect of Sodium Sulfate, Ammonium Chloride, Ammonium Nitrate, and Salt Mixtures on Aqueous Phase Partitioning of Organic Compounds.

Dissolved inorganic salts influence the partitioning of organic compounds into the aqueous phase. This influence is especially significant in atmospheric aerosol, which usually contains large amounts of ions, including sodium, ammonium, chloride, sulfate, and nitrate. However, empirical data on this salt effect are very sparse. Here, the partitioning of numerous organic compounds into solutions of Na2SO4, NH4Cl, and NH4NO3 was measured and compared with existing data for NaCl and (NH4)2SO4. Salt mixtures were also tested to establish whether the salt effect is additive. In general, the salt effect showed a decreasing trend of Na2SO4 > (NH)2SO4 > NaCl > NH4Cl > NH4NO3 for the studied organic compounds, implying the following relative strength of the salt effect of individual anions: SO42- > Cl- > NO3- and of cations: Na+ > NH4+. The salt effect of different salts is moderately correlated. Predictive models for the salt effect were developed based on the experimental data. The experimental data indicate that the salt effect of mixtures may not be entirely additive. However, the deviation from additivity, if it exists, is small. Data of very high quality are required to establish whether the effect of constituent ions or salts is additive or not.