Insights into the release of triclosan from microplastics in aquatic environment assessed with diffusive gradient in thin-films

Organic chemicals associated with microplastics (MPs) can be released and thus pose potential risks during weathering processes. However, the thermodynamics and kinetics of their release processes still need to be better understood. Herein, the adsorption and desorption kinetics of triclosan on polystyrene (PS) and polyvinyl chloride (PVC) were investigated by using both batch experiments and diffusive gradients in thin-films (DGT) technique. The pseudo-second-order model fitted the data best, implying that both intraparticle diffusion and external liquid film diffusion influence the adsorption and desorption processes. DGT continuously accumulated triclosan from MP suspensions but slower than theoretical values, indicating some restrictions to desorption. The DGT-induced fluxes in Soils/Sediment (DIFS) model, employed to interpret DGT data, gave distribution coefficients for labile species (K ) of 5000 mL g (PS) and 1000 mL g (PVC) and the corresponding response times (T ) were 10 s and 1000 s, respectively. Higher K but smaller T for PS than PVC showed that more triclosan adsorbed on PS could be rapidly released, while there were some kinetic limitations for triclosan on PVC. A novel finding was that pH and ionic strength individually and interactively affected the supply of triclosan to DGT. This is the first study to quantify interactions of organics with MPs by using DGT, aiding our understanding of MPs' adsorption/desorption behavior in the aquatic environment

The intake and clearance of PCBs in humans:A generic model of lifetime exposure

We have developed a model which successfully reconstructs the lifetime PCB-101 burden of the UK population for individuals born between 1920 and 1980. It not only follows burdens and clearance of persistent organic contaminants throughout a human lifetime - taking changes in age and body composition into account - but also, importantly, incorporates changing environmental concentrations of the compound of interest. Predicted results agree well with available measured lipid concentrations in human tissues. Its unique construction takes into account both changing environmental levels of PCBs in principal food groups and changing dietary habits during the time period. Because environmental burdens of persistent organic contaminants have changed over the last 60 years, residues in food will also have mirrored this change. Critically in this respect, the year in which an individual was born determines the shape and magnitude of their exposure profile for a given compound. Observed trends with age represent an historical legacy of exposure and are not simply a function of equal yearly cumulative inputs. We can demonstrate that the release profile of PCB-101 controls levels in the food supply and ultimately the burden of individuals throughout their life. This effect is expected to be similar for other PCB congeners and persistent organic compounds such as PCDD/Fs. Models of this type have important applications as predictive tools to estimate the likely impact of source-reduction strategies on human tissue concentrations

Temporal trends of polycyclic aromatic hydrocarbons in the UK atmosphere : 1991-2005.

Internationally there are few long-term air monitoring programs, which are necessary to assess the effectiveness of source abatement measures as required under the UNECE POPs protocol. In the United Kingdom, the Toxic Organic Micropollutants (TOMPS) program, funded by the Department for Environment, Food, and Rural Affairs (Defra), was started in 1991 and includes regular monitoring of a range of compounds including polycyclic aromatic hydrocarbons (PAHs). In this study, the time series (1991–2005) of atmospheric concentrations of 15 PAHs at six U.K. monitoring sites were investigated. Most show a statistically significant decrease in PAH levels over time, broadly consistent with the reported decline in emissions. Higher levels of heavier PAHs were noted in winter than in summer at most sites. At one coastal site, higher levels of lighter PAHs were noted in summer, possibly due to temperature-driven outgassing of these compounds from seawater. Current annual averages of benzo[a]pyrene are below the recently introduced annual air quality standard of 0.25 ng m−3 at all sites, although quarterly averages have exceeded 0.25 ng m−3 in recent years but only at the urban sites in winter. The atmospheric signature of total PAHs closely mirrors the emission signature, which lends strength to the idea that levels of PAHs in air are still mostly influenced by direct/local sources

Temporal trends in the sources of PCDD/Fs to and around the Venice Lagoon.

Two salt marsh cores were collected from the Venice Lagoon, Italy, and analysed for PCDD/Fs. The samples were undisturbed and had an approximately constant accumulation rate. Radiochemical chronologies were established for the different core sections. The PCDD/F pattern in the surficial layers was very similar to that of atmospheric deposition measured in the same area. However, the pattern changed with increasing depth and was very different in the deeper sections, where the highest PCDD/F concentrations were measured. This layer was dated around the 1950s. Deeper layers have a profile similar to the surficial one. Undisturbed salt marsh cores appear to be a reliable tool for the reconstruction of temporal trends in the atmospheric deposition of persistent organic pollutants. It is proposed that the trends in the core reflect atmospheric deposition that probably results from the sum of two different contributions: emissions of the industrial district of Porto Marghera on the edge of the lagoon and the regional background

Reconstruction of historical trends of PCDD/Fs and PCBs in the Venice Lagoon, Italy.

Historical trends of PCDD/Fs and PCBs from the year 1900 have been reconstructed for the Venice Lagoon area by using a fugacity-based dynamic multimedia model. A novel approach to estimate the inputs to the system was applied. Emissions to the lagoon were estimated by studying dated sediment cores taken from salt marshes located in the lagoon area. These cores have recently proven to be a suitable tool to reconstruct the temporal trends of atmospheric deposition of POPs. According to the model, concentrations of PCBs and PCDD/Fs in air and water reflect the trends of their production and usage, peaking during the 1960s. The peaks in the sediment were delayed by 5–40 years depending on the congener. Predicted concentrations are in good agreement with experimental results. The most important input parameters, identified by a sensitivity analysis, are the degradation constants, Kow, the Henry's law constant, vapour pressure, active sediment depth, sediment resuspension, and deposition rates, and water residence time in the lagoon

The maximum reservoir capacity of soils for persistent organic pollutants : implications for global cycling.

The concept of maximum reservoir capacity (MRC), the ratio of the capacities of the surface soil and of the atmospheric mixed layer (AML) to hold chemical under equilibrium conditions, is applied to selected persistent organic pollutants (POPs) in the surface ‘skin’ (1 mm) of soils. MRC is calculated as a function of soil organic matter (SOM) content and temperature-dependent KOA and mapped globally for selected PCB congeners (PCB-28; -153; -180) and HCB, to identify regions with a higher tendency to retain POPs. It is shown to vary over many orders of magnitude, between compounds, locations and time (seasonally/diurnally). The MRC approach emphasises the very large capacity of soils as a storage compartment for POPs. The theoretical MRC concept is compared to reality and its implications for the global cycling of POPs are discussed. Sharp gradients in soil MRC can exist in mountainous areas and between the land and ocean. Exchanges between oceans and land masses via the atmosphere is likely to be an important driver to the global cycling of these compounds, and net ocean–land transfers could occur in some areas. Major global terrestrial sinks/stores for POPs are identified and the significance of gradients between them discussed

Field deployment of thin film passive samplers (POGs) for persistent organic pollutants (POPs): a study in the urban atmospheric boundary layer.

This paper reports on the first field deployment of rapidly equilibrating thin-film passive air samplers under ambient conditions. The POlymer-coated Glass (POG) samplers have a coating of ethylene vinyl acetate (EVA) less than 1 μm thick applied to a glass surface. This can be dissolved off after exposure and prepared for the quantification of persistent organic pollutants (POPs) that have partitioned into the film during field exposure. In this study, POGs were deployed at various heights on the CN Tower in Toronto, Canada, to investigate the vertical distribution of selected compounds (PCBs, PAHs, organochlorine pesticides) in the atmospheric boundary layer of an urban area. The feasibility of the method to detect POPs from a few cubic meters of air was demonstrated, indicating the potential for rapid, low-volume sampling of air for ambient levels of POPs. PAH levels declined sharply with height, confirming ground-level emissions in urban areas as sources of these compounds; PCBs did the same, although less strongly. Different sampling events detected different vertical distributions of OC pesticides which could be related to local or distant sources, and variations in POPs on the samplers in these different events/heights demonstrate the dynamic nature of sources and atmospheric mixing of POPs

Challenges in assessing the environmental fate and exposure of nano silver

There are significant challenges in assessing the fate and exposure of nano particles (NPs) owing to the lack of information on their use and potential pathways and sinks in the environment. This paper discusses these issues using nanosilver as a case study. The approach taken is to assess the production of nanosilver, the range of products that utilise its properties, potential environmental release pathways and subsequent fate. Estimates of UK nanosilver released into the environment have been made and sewage sludge identified as an important receiving compartment. This work aims to highlight the on-going challenges faced when assessing NPs in the environment. Using nanosilver as an example, difficulties in assessing production, use and release are discussed. The study also recommends a potential approach to assess the fate and behaviour assessment of nanosilver in the environment