An evaluation of chemical persistence screening approaches

Bioaccumulation of PCBs and OCPs in Antarctic phytoplankton and zooplankton: Insights into bioconcentration and biomagnification in Fildes Bay

This study was conducted at Fildes Bay, King George Island, Antarctica, from November 30th, 2019, to January 30th, 2020. We determined the concentrations of Organochlorine Pesticides (OCPs) and Polychlorinated Biphenyls (PCBs) in phytoplankton, and zooplankton. The most abundant compounds found were hexachlorobenzene (HCB) in phytoplankton and γ-HCH in zooplankton. We estimated the bioconcentration factors (BCFPHYTO) for phytoplankton and zooplankton (BCFZOO), as well as biomagnification factors (BMF) across trophic levels. Our findings indicate that BCF values were generally higher for compounds with a higher degree of chlorination, and noticeable biomagnification of these contaminants was observed, emphasizing the enhancement of contaminant concentrations from phytoplankton to zooplankton. This biomagnification varied depending on the specific compound and environmental conditions. Throughout the study period, the factors influencing bioconcentration and biomagnification were closely correlated with the seasonal dynamics of the phytoplankton biomass, which were affected by local conditions such as slower S and SE winds. These events enhanced the concentration of chlorophyll-a and POPs, influencing their transfer across trophic levels. Our study underscores the complex interplay between biotic and abiotic factors in determining the fate of these persistent pollutants in a rapidly changing polar environment. These findings highlight the need for continuing ongoing monitoring to understand the long-term impacts of environmental changes on the distribution and behavior of hazardous substances in remote regions like Antarctica.

Occurrence and diffusive air-seawater exchanges of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in Fildes Bay, King George Island, Antarctica

We report the levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in seawater and air, and the air-sea dynamics through diffusive exchange analysis in Fildes Bay, King George Island, Antarctica, between November 2019 and January 30, 2020. Hexachlorobenzene (HCB) was the most abundant compound in both air and seawater with concentrations around 39 ± 2.1 pg m-3 and 3.2 ± 2.4 pg L-1 respectively. The most abundant PCB congener was PCB 11, with a mean of 3.16 ± 3.7 pg m-3 in air and 2.0 ± 1.1 pg L-1 in seawater. The fugacity gradient estimated for the OCP compounds indicate a predominance of net atmospheric deposition for HCB, α-HCH, γ-HCH, 4,4'-DDT, 4,4'-DDE and close to equilibrium for the PeCB compound. The observed deposition of some OCs may be driven by high biodegradation rates and/or settling fluxes decreasing the concentration of these compounds in surface waters, which is supported by the capacity of microbial consortium to degrade some of these compounds. The estimated fugacity gradients for PCBs showed differences between congeners, with net volatilization predominating for PCB-9, a trend close to equilibrium for PCB congeners 11, 28, 52, 101, 118, 138, and 153, and deposition for PCB 180. Snow amplification may play an important role for less hydrophobic PCBs, with volatilization predominating after snow/glacier melting. As hydrophobicity increases, the biological pump decreases the concentration of PCBs in seawater, reversing the fugacity gradient to atmospheric deposition. This study highlights the potential impacts of climate change, through glacier retreat, on the biogeochemistry of POPs, remobilizing those compounds previously trapped within the cryosphere which in turn will transform the Antarctic cryosphere into a secondary source of the more volatile POPs in coastal areas, influenced by snow and ice melting.

Role of Microbes in the degradation of organic semivolatile compounds in polar ecosystems: A review

The Arctic and the Antarctic Continent correspond to two eco-regions with extreme climatic conditions. These regions are exposed to the presence of contaminants resulting from human activity (local and global), which, in turn, represent a challenge for life forms in these environments. Anthropogenic pollution by semi-volatile organic compounds (SVOCs) in polar ecosystems has been documented since the 1960s. Currently, various studies have shown the presence of SVOCs and their bioaccumulation and biomagnification in the polar regions with negative effects on biodiversity and the ecosystem. Although the production and use of these compounds has been regulated, their persistence continues to threaten biodiversity and the ecosystem. Here, we summarize the current literature regarding microbes and SVOCs in polar regions and pose that bioremediation by native microorganisms is a feasible strategy to mitigate the presence of SVOCs. Our systematic review revealed that microbial communities in polar environments represent a wide reservoir of biodiversity adapted to extreme conditions, found both in terrestrial and aquatic environments, freely or in association with vegetation. Microorganisms adapted to these environments have the potential for biodegradation of SVOCs through a variety of genes encoding enzymes with the capacity to metabolize SVOCs. We suggest that a comprehensive approach at the molecular and ecological level is required to mitigate SVOCs presence in these regions. This is especially patent when considering that SVOCs degrade at slow rates and possess the ability to accumulate in polar ecosystems. The implications of SVOC degradation are relevant for the preservation of polar ecosystems with consequences at a global level.

Moving persistence assessments into the 21st century: A role for weight-of-evidence and overall persistence

Assessing the persistence of chemicals in the environment is a key element in existing regulatory frameworks to protect human health and ecosystems. Persistence in the environment depends on many fate processes, including abiotic and biotic transformations and physical partitioning, which depend on substances' physicochemical properties and environmental conditions. A main challenge in persistence assessment is that existing frameworks rely on simplistic and reductionist evaluation schemes that may lead substances to be falsely assessed as persistent or the other way around-to be falsely assessed as nonpersistent. Those evaluation schemes typically assess persistence against degradation half-lives determined in single-compartment simulation tests or against degradation levels measured in stringent screening tests. Most of the available test methods, however, do not apply to all types of substances, especially substances that are poorly soluble, complex in composition, highly sorptive, or volatile. In addition, the currently applied half-life criteria are derived mainly from a few legacy persistent organic pollutants, which do not represent the large diversity of substances entering the environment. Persistence assessment would undoubtedly benefit from the development of more flexible and holistic evaluation schemes including new concepts and methods. A weight-of-evidence (WoE) approach incorporating multiple influencing factors is needed to account for chemical fate and transformation in the whole environment so as to assess overall persistence. The present paper's aim is to begin to develop an integrated assessment framework that combines multimedia approaches to organize and interpret data using a clear WoE approach to allow for a more consistent, transparent, and thorough assessment of persistence. Integr Environ Assess Manag 2022;18:868-887. © 2021 ExxonMobil Biomedical Sciences, Inc. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Occurrence and air-water diffusive exchange legacy persistent organic pollutants in an oligotrophic north Patagonian lake

In this study, the occurrence and diffusive air-water exchange of POPs in Panguipulli Lake (39°42'S-72°13'W), an oligotrophic lake located in northern Patagonia (Chile), were determined. Air and water samples were collected between March and August 2017 (autumn-winter) and analyzed for concentrations of OCPs (α-HCH, β-HCH, γ-HCH and HCB) and PCBs (PCB-28,-52,-101,-118,-153,-158,-180) using gas chromatography coupled with an electron capture detector. The direction of air-water exchange direction was evaluated using a fugacity approach (ƒ_w ƒ_a^-1), and net diffusive exchange fluxes (F_AW, ng m^-2 d^-1) were also estimated. Total ∑₄OCP levels in air ranged from 0.31 to 37 pg m^-3, with a maximum for β-HCH, while Σ₇PCB levels ranged from 3.05 to 43 pg m^-3. The most abundant congener was PCB-153, accounting for 60% of the total PCBs in air. Surface water ∑₄OCPs measured in this study ranged from 1.01 to 3.9 pg L^-1, with γ-HCH predominating, while surface water Σ₇PCB levels ranged from 0.32 to 24 pg L^-1, with PCB-101, PCB-118, and PCB-153 presenting the highest levels. Diffusive air-water exchanges of HCB, α-HCH, γ-HCH and PCBs in the form of volatilization from the lake to air predominated; in contrast, for β-HCH net deposition dominated during the sampling period. Estimates suggested faster microbial degradation in the dissolved phase compared to atmospheric degradation for all analyzed POPs. Overall, these results could indicate that the oligotrophic lakes of northern Patagonia act as a secondary source of atmospheric POPs, mainly PCBs and some OCPs. This study is a first attempt to understand the occurrence of POPs in air and water, as well as their dynamics in oligotrophic lakes in the southern hemisphere.

Persistent organic pollutants in krill from the Bellingshausen, South Scotia, and Weddell Seas

Persistent organic pollutants (POPs) reach Antarctica through atmospheric transport, oceanic currents, and to minor extent, by migratory animals. The Southern Ocean is a net sink for many POPs, with a key contribution of the settling fluxes of POPs bound to organic matter (biological pump). However, little is known about POP transfer through the food web in the Southern Ocean and Antarctic waters, where krill is an important ecological node. In this study, we assessed the occurrence of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), polybrominated diphenyl ethers (PBDEs), and polychlorinated biphenyls (PCBs) in Antarctic krill (Euphausia superba) from the Bellingshausen, South Scotia and Weddell Seas around the Antarctic Peninsula. The concentrations of PCDD/Fs, PBDEs and PCBs in krill showed a large variability and the average were higher (generally within a factor 3) than those previously reported for eastern Antarctica. This result highlights regional differences related to atmospheric transport and deposition, and also probable regional sources due to human activities. Bioaccumulation and biomagnification factors for PCBs in krill were estimated using previously reported phytoplankton and seawater concentrations for this region. These suggested a near water-krill equilibrium for PCBs, which was not observed for water-phytoplankton partitioning. The estimated removal settling fluxes of PCBs due to the biological pump were several orders of magnitude higher than the estimated fluxes of PCBs transferred from phytoplankton to krill.

Occurrence and significance of polychlorinated biphenyls in water, sediment pore water and surface sediments of Umgeni River, KwaZulu-Natal, South Africa

The Umgeni River is one of the main sources of water in KwaZulu-Natal, South Africa; however; there is currently a lack of information on the presence and distribution of polychlorinated biphenyls (PCBs) in its sediment, sediment pore water and surface water. This study aims to determine the occurrence and significance of selected PCBs in the surface water, sediment pore water and surface sediment samples from the Umgeni River. Liquid-liquid and soxhlet extractions were used for water or pore water, and sediments, respectively. Extracts were cleaned up using a florisil column and analysed by gas chromatography-mass spectrometry. The total concentrations of eight polychlorinated biphenyls were 6.91-21.69 ng/mL, 40.67-252.30 ng/mL and 102.60-427.80 ng/g (dry weight), in unfiltered surface water, unfiltered sediment pore water and surface sediments, respectively. The percentage contributions of various matrices were 4, 36 and 60 % for unfiltered surface water, unfiltered pore water and sediment, respectively. The highest concentrations of PCBs were found in water, pore water and sediment collected from sampling sites close to the Northern Wastewater Treatment Works. The highest chlorinated biphenyl, PCB 180, was the most abundant at almost all sampling sites. To our knowledge, this is the first report on occurrence of polychlorinated biphenyls in the Umgeni River water, pore water and sediment system and our results provide valuable information regarding the partitioning of the PCBs between the water and sediment systems as well as the organic chemical quality of the water.

Meeting the challenge of identifying persistent pollutants at the state level

In 2007, the State of Oregon enacted legislation aimed at identifying persistent pollutants that could pose a threat to waters of the State and then reducing their discharge by means of a comprehensive pollution prevention program. This legislation defined a persistent pollutant as one that is toxic and persistent or bioaccumulative; a broad definition that required evaluation of an extensive number and variety of chemicals. The Oregon Department of Environmental Quality, in consultation with a science workgroup, implemented a 12-step process for identifying and prioritizing persistent pollutants consistent with this definition. This process is characterized by (a) maximum overall transparency in its conduct, including extensive public involvement, (b) 3 levels of objective and predefined criteria for categorization of a chemical as a persistent pollutant, (c) full disclosure of values and sources for all physicochemical data used for comparison with these criteria, and (d) clear acknowledgement when a chemical was identified as a persistent pollutant for reasons other than these criteria alone. This process was used to identify those chemicals relevant as persistent pollutants and to then prioritize them in terms of their relative ability to adversely impact waters of the state, with special emphasis on impacts to aquatic receptors. An initial list of 2130 chemicals was compiled from existing lists. Criteria for toxicity, persistence, and bioaccumulative potential were defined and then used with 2 different chemical property evaluation models (PBT Profiler and EPISuite) to produce a final list of 118 chemicals. The final list includes several legacy pollutants but also contains numerous current-use pharmaceuticals, personal care products, and pesticides, approximately half of which appear only once or not at all on lists compiled by others. Although it drew from the experience of others, assembling this list proved to be an exemplar of science in the service of policy.

3D-QSAR study on atmospheric half-lives of POPs using CoMFA and CoMSIA

3D-QSAR studies of persistent organic pollutants (POPs) screening for atmosphere persistence were performed by comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) methods. The mean and maximum half-life estimations for degradation in air of 49 UNEP POPs and possible POPs were modeled. Both groups' data have been modeled to obtain an average estimate and a predictive value for ranking and screening purposes. CoMFA and CoMSIA models have given cross-validation regression coefficient (q2) values of more than 0.69 and correlation coefficient (r2) value of more than 0.84, which validated for their prediction, could be applied to predict unavailable data.

Dynamic modeling of chemical fate and transport in multimedia environments at watershed scale-I: theoretical considerations and model implementation

A geo-referenced environmental fate model was developed for analyzing unsteady-state dispersion and distribution of chemicals in multimedia environmental systems. Chemical transport processes were formulated in seven environmental compartments of air, canopy, surface soil, root-zone soil, vadose-zone soil, surface water, and sediment. The model assumed that the compartments were completely mixed and chemical equilibrium was established instantaneously between the sub-compartments within each compartment. A fugacity approach was utilized to formulate the mechanisms of diffusion, advection, physical interfacial transport, and transformation reactions. The governing equations of chemical mass balances in the environmental compartments were solved simultaneously to reflect the interactions between the compartments. A geographic information system (GIS) database and geospatial analysis were integrated into the chemical transport simulation to provide spatially explicit estimations of model parameters at watershed scale. Temporal variations of the environmental properties and source emissions were also considered in the parameter estimations. The outputs of the model included time-dependent chemical concentrations in each compartment and its sub-compartments, and inter-media mass fluxes between adjacent compartments at daily time steps.

Relationship of approaches and a tiered methodology for screening chemicals in the context of long-range transport

In many national and international initiatives, where thousands of chemicals are screened, the ability of a chemical to be transported over long distances is an important criterion in determining whether environmental concern is warranted. Preliminary screening can be conducted using: (1) effective travel distance (ETD); (2) characteristic travel distance (CTD); and/or (3) the degradation half-life in air. The CTD is the distance traveled before the concentration of a chemical in air is reduced by a factor of 50%, for example. Differences in the distance traveled associated with the environmental release medium of a chemical are taken into account the ETD measure. The ETD can be defined as the distance traveled before the concentration in a stated medium (air, water, soil or sediment) is reduced to a specified level for a given mass release rate to air, to water and/or to soil. However, despite their merits, the use of multimedia screening measures like the ETD and CTD remains inhibited by both the limited availability of degradation data (particularly for soils and sediments) and release pattern information. Preliminary screening in terms of the atmospheric degradation half-life is commonly the only practical option. In this paper, straightforward guidelines based on partitioning coefficients (Henry's law constant and octanol water partitioning coefficient) are proposed to reduce the degradation data requirements of multimedia measures like the ETD and CTD. The values used in the guidelines reflect a quantifiable trade-off between data acquisition requirements and uncertainty. The relationship of the potential screening options (using all degradation data versus using only data identified as required in the CTD and ETD approaches; screening in terms of the degradation half-life in air versus the CTD versus the ETD) is derived and the consequences of the differences are illustrated. A three-tiered screening methodology is then proposed. This tiered methodology will result in significant savings in time and money in national and international screening initiatives.