Organic Contaminants Of Concern Research Articles

Uncovering transformation products of four organic contaminants of concern by photodegradation experiments and analysis of real samples from a local river

In this study, photodegradation experiments simulating the exposure conditions of sunlight on the commonly detected in surface and wastewater contaminants atorvastatin (ATV), bezafibrate (BEZ), oxybenzone (OXZ), and tris(2-butoxyethyl)phosphate (TBEP) were conducted as the fate of these compounds and their transformation products (TPs) was followed. Then a nontargeted analysis was carried out on an urban river to confirm the environmental occurrence of the TPs after which the ECOSAR software was used to generate predicted effect levels of toxicity of the detected TPs on aquatic organisms. Five TPs of ATV were tentatively identified including two stable ones at the end of the experiment: ATV_TP557a and ATV_TP575, that were the product of hydroxylation. Complete degradation of OXZ was observed in the experiment with no significant TP identified. BEZ remained stable and largely undegraded at the end of the exposure. Five TPs of TBEP were found including four that were stable at the end of the experiment: TBEP_TP413, TBEP_TP415, TBEP_TP429, and TBEP_TP343. In the nontargeted analysis, ATV_TP557b, a positional isomer of ATV_TP557a, ATV_TP575 and the 5 TPs of TBEP were tentatively identified. The predicted concentration for effect levels were lower for ATV_TP557b compared to ATV indicating the TP is potentially more toxic than the parent compound. All the TPs of TBEP showed lower predicted toxicity toward aquatic organisms than their parent compound. These results highlight the importance of conducting complete workflows from laboratory experiments, followed by nontargeted analysis to confirm environmental occurrence to end with predicted toxicity to better communicate concern of the newfound TPs to monitoring programs.

Degradation and Defluorination of Aqueous Perfluorooctane Sulfonate by Silica-Based Granular Media Using Batch Reactors

Per- and polyfluoroalkyl substances (PFASs) are recalcitrant emerging contaminants of concern within the United States and internationally. Of the known PFASs, the sulfonates are considered among the most toxic and difficult to destroy using traditional methods. Research presented herein describes the degradation and defluorination of perfluorooctane sulfonate (PFOS) using a novel photocatalytic porous silica-based granular media (SGM) activated with ultraviolet light, and combined with a strong or weak nucleophilic attack in batch reactors. Sodium thiosulfate proved to be the most compatible and efficient nucleophile in combination with SGM media production of free radicals. Measured aqueous fluoride content accounted for 51% defluorination of PFOS, while the remainder is theorized to mineralize and reside within the porous network of the SGM, as indicated by scanning electron microscopy and energy dispersive x-ray spectroscopy. Removal of PFOS in solution is completed by 30 min with Na2S2O3, with measurable by-product production of C2F3O2− and aqueous fluoride occurring at 15 min. The rapid increase, incipient decrease, and subsequent mineralization of fluoride reveals that the degradation of PFOS is rapid and starts with cleaving of the functional sulfonate group. Amalgamated C-F chains precipitate within the SGM alongside the crystalized fluorine. Possible pathways for PFOS destruction are proposed for the combined attack results. This approach is translatable to other PFASs and organic contaminants of concern.

Is rain or snow a more efficient scavenger of organic chemicals?

Abstract Calculations of equilibrium partitioning in the atmosphere are used to quantify and compare the capacity of rain and snow to scavenge gaseous and particle-bound organic contaminants from the atmosphere at different temperatures. Whether snow or rain is more efficient in scavenging organic contaminants depends on the characteristics of the chemical, the characteristics of the snow and atmospheric temperature. At 0°C rain is typically more effective in scavenging the vapors of small organic molecules than snow, because the capacity of the snow surface to sorb such chemicals is smaller than that of liquid water droplets. Snow will, however, be a more effective scavenger for vapors of larger, non-polar organic compounds, which are only sparingly water soluble. The mode of scavenging (vapor vs. particles) and the total scavenging efficiency for such substances will be highly variable and dependent on temperature and the snow characteristics, namely the particle scavenging ratio and the specific snow surface area. To be effectively scavenged by snow, chemicals either need to have an adsorption coefficient at the snow surface KSA of >0.1 m or a particle–air partition coefficient KParticle/Air of >1011 at temperatures below 0°C. Many organic contaminants of concern have such properties. As temperature decreases, more of a chemical partitions from the vapor phase to liquid water droplets, atmospheric particles and the snow surface. This temperature effect is the main reason that snow scavenging ratios are often higher than rain scavenging ratios, especially below −10°C. It is also the reason why wet deposition processes become increasingly important with decreasing temperature, and even constitute the dominant deposition mechanism for some organic contaminants in cold environments.

Is rain or snow a more efficient scavenger of organic chemicals?

Calculations of equilibrium partitioning in the atmosphere are used to quantify and compare the capacity of rain and snow to scavenge gaseous and particle-bound organic contaminants from the atmosphere at different temperatures. Whether snow or rain is more efficient in scavenging organic contaminants depends on the characteristics of the chemical, the characteristics of the snow and atmospheric temperature. At 0°C rain is typically more effective in scavenging the vapors of small organic molecules than snow, because the capacity of the snow surface to sorb such chemicals is smaller than that of liquid water droplets. Snow will, however, be a more effective scavenger for vapors of larger, non-polar organic compounds, which are only sparingly water soluble. The mode of scavenging (vapor vs. particles) and the total scavenging efficiency for such substances will be highly variable and dependent on temperature and the snow characteristics, namely the particle scavenging ratio and the specific snow surface area. To be effectively scavenged by snow, chemicals either need to have an adsorption coefficient at the snow surface KSA of >0.1 m or a particle–air partition coefficient KParticle/Air of >1011 at temperatures below 0°C. Many organic contaminants of concern have such properties. As temperature decreases, more of a chemical partitions from the vapor phase to liquid water droplets, atmospheric particles and the snow surface. This temperature effect is the main reason that snow scavenging ratios are often higher than rain scavenging ratios, especially below −10°C. It is also the reason why wet deposition processes become increasingly important with decreasing temperature, and even constitute the dominant deposition mechanism for some organic contaminants in cold environments.

Treating contaminated sediment with a two-stage base-catalyzed decomposition (BCD) process: bench-scale evaluation

The New York/New Jersey (NY/NJ) Harbor estuary sediment contains polychlorinated dibenzo- p-dioxins/furans ( PCDDs PCDFs ), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and chlorinated pesticides. The U.S. EPA-developed two-stage base-catalyzed decomposition (BCD) process was tested for removal and decomposition of these organic contaminants of concern (OCCs) from the sediment. The Stage 1 process removed OCCs to below the limits of analytical quantitation (LAQs) or the limits of the potentially applicable requirements (LPARs), and concentrated OCCs into a small volume of organic condensate for Stage 2 chemical destruction. The aqueous condensate fractions contained some nondestroyed contaminants, either at levels below LPARs or at levels that could be treated by conventional treatment processes. Factors such as chemical addition, water content, and residence time were examined for their effects on the treatment process. Mass balances were calculated. The distribution of metal contaminants was determined.