Determining chemical air equivalency using silicone personal monitors

BACKGROUND

Silicone personal samplers are increasingly being used to measure chemical exposures, but many of these studies do not attempt to calculate environmental concentrations.

OBJECTIVE

Using measurements of silicone wristband uptake of organic chemicals from atmospheric exposure, create log K_sa and k_e predictive models based on empirical data to help develop air equivalency calculations for both volatile and semi-volatile organic compounds.

METHODS

An atmospheric vapor generator and a custom exposure chamber were used to measure the uptake of organic chemicals into silicone wristbands under simulated indoor conditions. Log K_sa models were evaluated using repeated k-fold cross-validation. Air equivalency was compared between best-performing models.

RESULTS

Log K_sa and log k_e estimates calculated from uptake data were used to build predictive models from boiling point (BP) and other parameters (all models: R² = 0.70-0.94). The log K_sa models were combined with published data and refined to create comprehensive and effective predictive models (R²: 0.95-0.97). Final estimates of air equivalency using novel BP models correlated well over an example dataset (Spearman r = 0.984) across 5-orders of magnitude (<0.05 to >5000 ng/L).

SIGNIFICANCE

Data from silicone samplers can be translated into air equivalent concentrations that better characterize environmental concentrations associated with personal exposures and allow direct comparisons to regulatory levels.

Preparation and performance features of wristband samplers and considerations for chemical exposure assessment

Wristbands are increasingly used for assessing personal chemical exposures. Unlike some exposure assessment tools, guidelines for wristbands, such as preparation, applicable chemicals, and transport and storage logistics, are lacking. We tested the wristband's capacity to capture and retain 148 chemicals including polychlorinated biphenyls (PCBs), pesticides, flame retardants, polycyclic aromatic hydrocarbons (PAHs), and volatile organic chemicals (VOCs). The chemicals span a wide range of physical-chemical properties, with log octanol-air partitioning coefficients from 2.1 to 13.7. All chemicals were quantitatively and precisely recovered from initial exposures, averaging 102% recovery with relative SD ≤21%. In simulated transport conditions at +30 °C, SVOCs were stable up to 1 month (average: 104%) and VOC levels were unchanged (average: 99%) for 7 days. During long-term storage at -20 °C up to 3 (VOCs) or 6 months (SVOCs), all chemical levels were stable from chemical degradation or diffusional losses, averaging 110%. Applying a paired wristband/active sampler study with human participants, the first estimates of wristband-air partitioning coefficients for PAHs are presented to aid in environmental air concentration estimates. Extrapolation of these stability results to other chemicals within the same physical-chemical parameters is expected to yield similar results. As we better define wristband characteristics, wristbands can be better integrated in exposure science and epidemiological studies.

PAH and OPAH Flux during the Deepwater Horizon Incident

Passive sampling devices were used to measure air vapor and water dissolved phase concentrations of 33 polycyclic aromatic hydrocarbons (PAHs) and 22 oxygenated PAHs (OPAHs) at four Gulf of Mexico coastal sites prior to, during and after shoreline oiling from the Deepwater Horizon oil spill (DWH). Measurements were taken at each site over a 13 month period, and flux across the water-air boundary was determined. This is the first report of vapor phase and diffusive flux of both PAHs and OPAHs during the DWH. Vapor phase sum PAH and OPAH concentrations ranged between 6.6 and 210 ng/m(3) and 0.02 and 34 ng/m(3) respectively. PAH and OPAH concentrations in air exhibited different spatial and temporal trends than in water, and air-water flux of 13 individual PAHs was shown to be at least partially influenced by the DWH incident. The largest PAH volatilizations occurred at the sites in Alabama and Mississippi at nominal rates of 56 000 and 42 000 ng/m(2) day(-1) in the summer. Naphthalene was the PAH with the highest observed volatilization rate of 52 000 ng/m(2) day(-1) in June 2010. This work represents additional evidence of the DWH incident contributing to air contamination, and provides one of the first quantitative air-water chemical flux determinations with passive sampling technology.

Using silicone wristbands to evaluate preschool children's exposure to flame retardants

Silicone wristbands can be used as passive sampling tools for measuring personal environmental exposure to organic compounds. Due to the lightweight and simple design, the wristband may be a useful technique for measuring children's exposure. In this study, we tested the stability of flame retardant compounds in silicone wristbands and developed an analytical approach for measuring 41 flame retardants in the silicone wristband in order to evaluate exposure to these compounds in preschool-aged children. To evaluate the robustness of using wristbands to measure flame retardants, we evaluated the stability of 3 polybrominated diphenyl ethers (BDEs), and 2 organophosphate flame retardants (OPFRs) in wristbands over 84 days and did not find any evidence of significant loss over time at either 4 or -20°C (p>0.16). We recruited a cohort of 92 preschool aged children in Oregon to wear the wristband for 7 days in order to characterize children's acceptance of the technology, and to characterize their exposure to flame retardants. Seventy-seven parents returned the wristbands for analysis of 35 BDEs, 4 OPFRs, and 2 other brominated flame retardants although 5 were excluded from the exposure assessment due to protocol deviations (n=72). A total of 20 compounds were detected above the limit of quantitation, and 11 compounds including 4 OPFRs and 7 BDEs were detected in over 60% of the samples. Children's gender, age, race, recruitment site, and family context were not significantly associated with returning wristbands or compliance with protocols. Comparisons between flame retardant data and socio-demographic information revealed significant differences in total exposures to both ΣBDEs and ΣOPFRs based on age of house, vacuuming frequency, and family context. These results demonstrate that preschool children in Oregon are exposed to BDEs that are no longer being produced in the United States and to OPFRs that have been used as an alternative to polybrominated compounds. Silicone wristbands were well tolerated by young children and were useful for characterizing personal exposure to flame retardants that were not bound to particulate matter.

In vivo contaminant partitioning to silicone implants: Implications for use in biomonitoring and body burden

Silicone polymers are used for a wide array of applications from passive samplers in environmental studies, to implants used in human augmentation and reconstruction. If silicone sequesters toxicants throughout implantation, it may represent a history of exposure and potentially reduce the body burden of toxicants influencing the risk of adverse health outcomes such as breast cancer. Objectives of this research included identifying a wide variety of toxicants in human silicone implants, and measuring the in vivo absorption of contaminants into silicone and surrounding tissue in an animal model. In the first study, eight human breast implants were analyzed for over 1400 organic contaminants including consumer products, chemicals in commerce, and pesticides. A total of 14 compounds including pesticides such as trans-nonachlor (1.2-5.9ng/g) and p,p'-DDE (1.2-34ng/g) were identified in human implants, 13 of which have not been previously reported in silicone prostheses. In the second project, female ICR mice were implanted with silicone and dosed with p,p'-DDE and PCB118 by intraperitoneal injection. After nine days, silicone and adipose samples were collected, and all implants in dosed mice had p,p'-DDE and PCB118 present. Distribution ratios from silicone and surrounding tissue in mice compare well with similar studies, and were used to predict adipose concentrations in human tissue. Similarities between predicted and measured chemical concentrations in mice and humans suggest that silicone may be a reliable surrogate measure of persistent toxicants. More research is needed to identify the potential of silicone implants to refine the predictive quality of chemicals found in silicone implants.

Improvements in pollutant monitoring: optimizing silicone for co-deployment with polyethylene passive sampling devices

Sequestering semi-polar compounds can be difficult with low-density polyethylene (LDPE), but those pollutants may be more efficiently absorbed using silicone. In this work, optimized methods for cleaning, infusing reference standards, and polymer extraction are reported along with field comparisons of several silicone materials for polycyclic aromatic hydrocarbons (PAHs) and pesticides. In a final field demonstration, the most optimal silicone material is coupled with LDPE in a large-scale study to examine PAHs in addition to oxygenated-PAHs (OPAHs) at a Superfund site. OPAHs exemplify a sensitive range of chemical properties to compare polymers (log Kow 0.2-5.3), and transformation products of commonly studied parent PAHs. On average, while polymer concentrations differed nearly 7-fold, water-calculated values were more similar (about 3.5-fold or less) for both PAHs (17) and OPAHs (7). Individual water concentrations of OPAHs differed dramatically between silicone and LDPE, highlighting the advantages of choosing appropriate polymers and optimized methods for pollutant monitoring.

Passive sampling coupled to ultraviolet irradiation: a useful analytical approach for studying oxygenated polycyclic aromatic hydrocarbon formation in bioavailable mixtures

The authors investigated coupling passive sampling technologies with ultraviolet irradiation experiments to study polycyclic aromatic hydrocarbon (PAH) and oxygenated PAH transformation processes in real-world bioavailable mixtures. Passive sampling device (PSD) extracts were obtained from coastal waters impacted by the Deepwater Horizon oil spill and Superfund sites in Portland, Oregon, USA. Oxygenated PAHs were found in the contaminated waters with our PSDs. All mixtures were subsequently exposed to a mild dose of ultraviolet B (UVB). A reduction in PAH levels and simultaneous formation of several oxygenated PAHs were measured. Site-specific differences were observed with UVB-exposed PSD mixtures.

Perfluoroalkyl contaminants in plasma of five sea turtle species: comparisons in concentration and potential health risks

The authors compared blood plasma concentrations of 13 perfluoroalkyl contaminants (PFCs) in five sea turtle species with differing trophic levels. Wild sea turtles were blood sampled from the southeastern region of the United States, and plasma was analyzed using liquid chromatography tandem mass spectrometry. Mean concentrations of perfluorooctane sulfonate (PFOS), the predominant PFC, increased with trophic level from herbivorous greens (2.41 ng/g), jellyfish-eating leatherbacks (3.95 ng/g), omnivorous loggerheads (6.47 ng/g), to crab-eating Kemp's ridleys (15.7 ng/g). However, spongivorous hawksbills had surprisingly high concentrations of PFOS (11.9 ng/g) and other PFCs based on their trophic level. These baseline concentrations of biomagnifying PFCs demonstrate interesting species and geographical differences. The measured PFOS concentrations were compared with concentrations known to cause toxic effects in laboratory animals, and estimated margins of safety (EMOS) were calculated. Small EMOS (<100), suggestive of potential risk of adverse health effects, were observed for all five sea turtle species for immunosuppression. Estimated margins of safety less than 100 were also observed for liver, thyroid, and neurobehavorial effects for the more highly exposed species. These baseline concentrations and the preliminary EMOS exercise provide a better understanding of the potential health risks of PFCs for conservation managers to protect these threatened and endangered species.

Determination of perfluorinated alkyl acid concentrations in biological standard reference materials

Standard reference materials (SRMs) are homogeneous, well-characterized materials used to validate measurements and improve the quality of analytical data. The National Institute of Standards and Technology (NIST) has a wide range of SRMs that have mass fraction values assigned for legacy pollutants. These SRMs can also serve as test materials for method development, method validation, and measurement for contaminants of emerging concern. Because inter-laboratory comparison studies have revealed substantial variability of measurements of perfluoroalkyl acids (PFAAs), future analytical measurements will benefit from determination of consensus values for PFAAs in SRMs to provide a means to demonstrate method-specific performance. To that end, NIST, in collaboration with other groups, has been measuring concentrations of PFAAs in a variety of SRMs. Here we report levels of PFAAs and perfluorooctane sulfonamide (PFOSA) determined in four biological SRMs: fish tissue (SRM 1946 Lake Superior Fish Tissue, SRM 1947 Lake Michigan Fish Tissue), bovine liver (SRM 1577c), and mussel tissue (SRM 2974a). We also report concentrations for three in-house quality-control materials: beluga whale liver, pygmy sperm whale liver, and white-sided dolphin liver. Measurements in SRMs show an array of PFAAs, with perfluorooctane sulfonate (PFOS) being the most frequently detected. Reference and information values are reported for PFAAs measured in these biological SRMs.

Spatial and temporal trends of perfluorinated compounds in Beluga Whales (Delphinapterus leucas) from Alaska

Wildlife from remote locations have been shown to bioaccumulate perfluorinated compounds (PFCs) in their tissues. Twelve PFCs, consisting of perfluorinated carboxylic (PFCA) and sulfonic (PFSA) acids as well as the perfluorooctane sulfonate (PFOS) precursor perfluorooctane sulfonamide (PFOSA), were measured in livers of 68 beluga whales (Delphinapterus leucas) collected from two subpopulations, Cook Inlet and eastern Chukchi Sea, in Alaska between 1989 and 2006. PFOS and PFOSA were the dominant compounds measured in both beluga stock populations, with overall median concentrations of 10.8 ng/g and 22.8 ng/g, respectively. Long-chain perfluorocarboxylates, PFCAs (9 to 14 carbons), were detected in more than 80% of the samples. Perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTriA) made up a large percentage of the PFCAs measured with median concentrations of 8.49 ng/g and 4.38 ng/g, respectively. To compare differences in location, year, sex, and length, backward stepwise multiple regression models of the individual and total PFC concentrations were used. Spatially, the Cook Inlet belugas had higher concentrations of most PFCAs and PFOS (p < 0.05); however, these belugas had a lower median concentration of PFOSA when compared to belugas from the eastern Chukchi Sea (p < 0.05). Temporal trends indicated most PFCAs, PFHxS, PFOS, and PFOSA concentrations increased from 1989 to 2006 (p < 0.05). Males had significantly higher concentrations of PFTriA, ΣPFCA, and PFOS (p < 0.05). Perfluorononanic acid (PFNA) and PFOS showed a significant decrease in concentration with increasing animal length (p < 0.05). These observations suggest the accumulation of PFCs in belugas is influenced by year, location, sex, and length.

Temporal and spatial trends of perfluorinated compounds in juvenile loggerhead sea turtles (Caretta caretta) along the East Coast of the United States

Perfluorinated compounds (PFCs) are globally distributed persistent environmental contaminants. This study provides temporal trends as well as large-scale spatial trends of PFC concentrations in threatened juvenile loggerhead sea turtles near or from Florida Bay (FL Bay), Cape Canaveral (FL), Charleston (SC), Core Sound (NC), and Chesapeake Bay (MD). PFCs were extracted from 163 plasma and serum samples using solid-phase extraction and quantified with LC-MS/MS. Concentrations of six compounds significantly varied by site, with MD or FL Bay turtles having the highest concentrations. Perfluorooctane sulfonate (PFOS) was the predominant PFC at all sites (range: 0.31 ng/g to 39.0 ng/g). FL Bay turtles, compared to other sites, accumulated a unique PFC pattern with a higher proportion of perfluorocarboxylates compared to PFOS. Furthermore, this study was the first to statistically correlate wildlife PFC concentrations with human population, used as a proxy for urbanization and sources of PFCs to the environment. Positive relationships were found in which human population accounted for 75 and 81% of the variance in turtle PFOS and perfluoroundecanoate (PFUnA) concentrations (p = 0.06 and 0.04), respectively. PFOS and perfluorononanoate (PFNA) significantly decreased from 2000-2008 in SC turtles annually by 20 and 11%, respectively (p </= 0.02). Future investigations should continue temporal assessments as PFC regulations change, attempt to pinpoint specific sources and transport pathways in areas with unique PFC patterns, and assess turtle health at sites with higher PFC concentrations.