Particle size distribution of halogenated flame retardants and implications for atmospheric deposition and transport.

This study investigates the distribution of polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD) and a group of novel flame retardants (NFRs) on atmospheric aerosols. Two high volume cascade impactors were used to collect particulate fractions of ambient air over a one year period at urban and rural sites. The majority of FRs were found on the finest aerosols (<0.95 µm). Concentrations of HBCD were higher than those of ΣPBDEs. Moreover, we noted seasonality and spatial differences in particle size distributions, yet a large portion of the observed differences were due to differences in particulate matter (PM) itself. When normalized by PM, the size distributions of the FRs exhibited much greater heterogeneity. Differences existed between the FR distributions by molecular weight, with the higher molecular weight FRs (e.g., BDE-209, Dechlorane Plus) distributed more uniformly across all particulate size fractions. The seasonal, spatial, and compound-specific differences are of crucial importance when estimating dry and wet deposition of FRs as smaller aerosols have longer atmospheric residence times. Estimated wet and dry deposition of four representative FRs (BDE-47, BDE-209, HBCD, and Dechlorane Plus) using size-segregated aerosol data resulted in lower deposition estimates than when bulk aerosol data were used. This has implications for estimates of long-range atmospheric transport and atmospheric residence times, as it suggests that without size-specific distributions, these parameters could be underestimated for FRs.

Chasing equilibrium passive sampling of hydrophobic organic compounds in water.

We investigated a combination of approaches to extend the attainment of partition equilibria between silicone passive samplers (samplers) and surface or treated waste water towards more hydrophobic organic compounds (HOC). The aim was to identify the HOC hydrophobicity range for which silicone sampler equilibration in water is feasible within a reasonable sampler deployment period. Equilibrium partitioning of HOC between sampler and water is desirable for a simpler application as a "chemometer", aiming to compare chemical activity gradients across environmental media (e.g. water, sediment, biota). The tested approaches included a) long sampler exposure periods and high water flow to maximize mass transfer from water to sampler; b) the use of samplers with reduced sheet thicknesses; and c) pre-equilibration of samplers with local bottom sediment, followed by their exposure in surface water at the same sampling site. These approaches were tested at three sites including a fish pond with a low level of pollution, a river impacted by an urban agglomeration and an effluent of municipal wastewater treatment plant. Tested compounds included polychlorinated biphenyls (PCB), polycyclic aromatic hydrocarbons (PAH), DDT, its metabolites and their isomers, hexachlorobenzene (HCB) and polybrominated diphenyl ethers (PBDE). The study shows that samplers with a surface area of 400-800 cm2 consisting of thin (100-500 µm) silicone sheets exposed at sampling rates of 10-40 L d-1 for a time period of up to four months reach partition equilibrium with water for compounds with log Kow ≤ 5.5. Nevertheless, for compounds beyond this limit it is challenging, within a reasonable time period, to reach equilibrium between sampler and water in an open system where water boundary layer resistance controls the mass transfer. For more hydrophobic HOC (log Kow > 6), the kinetic method using performance reference compounds is recommended instead.

Hexabromocyclododecane: concentrations and isomer profiles from sources to environmental sinks.

Concentrations and isomer compositions of hexabromocyclododecane (HBCD) were measured in six matrices in the Czech Republic (HBCD technical mixture; consumer products; indoor and outdoor air at industrial, urban and background locations; soils; and sediments) to provide insight into changes in concentrations and isomer profiles between environmental sources and environmental sinks. A distinct gradient of air concentrations was observed, from 1600 ng/m3 in the industrial area to < 10 pg/m3 in urban and background air. Isomer profiles also showed a distinct gradient in air, from 95% γ-HBCD in industrial air to 40% γ-HBCD in background air, suggesting the influence of differential atmospheric transport and phototransformation of γ- to α-HBCD. Concentrations and isomer compositions in consumer products were highly variable and indicated differences between products with intentional addition of HBCD as a flame retardant versus those with HBCD as an impurity, e.g., from recycled plastic. Understanding the isomer-specific environmental distributions and processes remains important for risk assessment and toxicology, considering the continued use of HBCD and the isomer-specific differences in uptake, metabolism, and toxicity, and further, demonstrates the utility of isomer profiles to better understand environmental processes of HBCDs.

Mobile dynamic passive sampling of trace organic compounds: Evaluation of sampler performance in the Danube River.

A "dynamic" passive sampling (DPS) device, consisting of an electrically driven large volume water pumping device coupled to a passive sampler exposure cell, was designed to enhance the sampling rate of trace organic compounds. The purpose of enhancing the sampling rate was to achieve sufficient method sensitivity, when the period available for sampling is limited to a few days. Because the uptake principle in the DPS remains the same as for conventionally-deployed passive samplers, free dissolved concentrations can be derived from the compound uptake using available passive sampler calibration parameters. This was confirmed by good agreement between aqueous concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) derived from DPS and conventional caged passive sampler. The DPS device enhanced sampling rates of compounds that are accumulated in samplers under water boundary layer control (WBL) more than five times compared with the conventionally deployed samplers. The DPS device was deployed from a ship cruising downstream the Danube River to provide temporally and spatially integrated concentrations. A DPS-deployed sampler with surface area of 400cm2 can reach sampling rates up to 83Ld-1. The comparison of three passive samplers made of different sorbents and co-deployed in the DPS device, namely silicone rubber (SR), low density polyethylene (LDPE) and SDB-RPS Empore™ disks showed a good correlation of surface specific uptake for compounds that were sampled integratively during the entire exposure period. This provided a good basis for a cross-calibration between the samplers. The good correlation of free dissolved PAHs, PCBs and HCB concentration estimates obtained using SR and LDPE confirmed that both samplers are suitable for the identification of concentration gradients and trends in the water column. We showed that the differences in calculated aqueous concentrations between sampler types are mainly associated with different applied uptake models.

Effect-based monitoring of the Danube River using mobile passive sampling.

Many aquatic pollutants can be present at low concentrations, but their mixtures can still affect health or behavior of exposed organisms. In this study, toxicological and chemical analyses were combined for spatial contamination profiling using an innovative passive sampling approach. A novel Dynamic Passive Sampler (DPS) was employed as a mobile sampler from a ship cruising along 2130km of the Danube river during the Joint Danube Survey 3 (JDS3). The sampling was performed in eight subsequent river stretches with two types of complementary passive samplers: silicone rubber sheets (SR) used for non-polar chemicals and SDB-RPS Empore™ disks (ED) for more hydrophilic compounds. Besides extensive chemical analyses, the bioactivity of samples was characterized by a battery of reporter gene bioassays. Cross-calibration of the employed passive samplers enabled robust estimation of water concentrations applicable for compounds with a wide range of physicochemical properties. DPS was suitable for sampling of water contaminants even at pgL-1 levels, with 209 of 267 analyzed compounds detected in the samples. Biological effects were detected in both ED and SR extracts across all river stretches by bioassays focused on xenobiotic metabolism mediated by the aryl hydrocarbon and pregnane X receptors, endocrine disruptive potential mediated by estrogen and androgen receptors and the oxidative stress response. The bioassay responses expressed as bioanalytical equivalent concentrations (BEQbio) were comparable with data obtained from large volume active sampling. The extracts of the ED samplers were more biologically active than extracts of SR samplers. Except of estrogenicity, where the analyzed chemicals explained on average 62% of the effects in ED samples, the detected chemicals explained <8% of BEQbio values. The study shows the utility of the combination of the innovative passive sampling approach with effect-based tools for efficient and fast monitoring even in water bodies with relatively low levels of contamination.