J.R. Parsons

Biodegradation of Perfluorinated Compounds

The information available in the literature provides evidence for the biodegradation of some poly- and per-fluorinated compounds, but such biodegradation is incomplete and may not result in mineralization. Recent publications have demonstrated that 8:2 fluorotelomer alcohol, for example, can be degraded by bacteria from soil and wastewater treatment plants to perfluorooctanoic acid. Similarly, 2-N-ethyl(perfluorooctane sulfonamido)ethanol can be degraded by wastewater treatment sludge to perfluorooctanesulfonate. It is presently unclear whether these two products are degraded further. Therefore, the question remains as to whether there is a potential for defluorination and biodegradation of PFCs that contributes significantly to their environmental fate. The lack of mineralization observed is probably caused by the stability of the C-F bond, although there are examples of microbially catalyzed defluorination reactions. As is the case with reductive dechlorination or debromination, reductive defluorination is energetically favorable under anaerobic conditions and releases more energy than that available from sulfate reduction or methanogenesis. Consequently, we should consider the possibility that bacteria will adapt to utilize this source of energy, although evolving mechanisms to overcome the kinetic barriers to degradation of these compounds may take some time. The fact that such reactions are absent for some PFCs, to date, may be because too little time has passed for microorganisms to adapt to these potential substrates. Hence, the situation may be comparable to that of chlorinated organic compounds several decades ago. For many years, organochlorine compounds were considered to be catabolically recalcitrant; today, reductive chlorination reactions of many organochlorines, including PCBs and dioxins, are regularly observed in anaerobic environments. Hence, it is opportune and important to continue studying the potential degradation of perfluorinated compounds in carefully designed experiments with either microbial populations from contaminated sites or cultures of bacteria known to dehalogenate chlorinated compounds.

Degradation of halogenated aromatic compounds

Due to their persistence, haloaromatics are compounds of environmental concern. Aerobically, bacteria degrade these compounds by mono- or dioxygenation of the aromatic ring. The common intermediate of these reactions is (halo)catechol. Halocatechol is cleaved either intradiol (ortho-cleavage) or extradiol (meta-cleavage). In contrast to ortho-cleavage, meta-cleavage of halocatechols yields toxic metabolites. Dehalogenation may occur fortuitously during oxygenation. Specific dehalogenation of aromatic compounds is performed by hydroxylases, in which the halo-substituent is replaced by a hydroxyl group. During reductive dehalogenation, haloaromatic compounds may act as electron-acceptors. Herewith, the halo-substituent is replaced by a hydrogen atom.

Elucidation of the metabolic pathway of fluorene and cometabolic pathways of phenanthrene, fluoranthene, anthracene and dibenzothiophene by Sphingomonas sp. LB126.

The metabolic pathway of the PAH fluorene and the cometabolic pathway of the PAHs phenanthrene, fluoranthene, anthracene and dibenzothiophene in Sphingomonas sp. LB126 were examined. To our knowledge this is the first study on the cometabolic degradation of the three-ring PAHs phenanthrene, anthracene and the four-ring PAH fluoranthene by a fluorene-utilizing species. Metabolism of fluorene was shown to proceed via the 9-fluorenone pathway to form o-phthalic acid and protocatechuic acid. The cometabolic mono-hydroxylation found for phenanthrene, fluoranthene and anthracene shows similarity with the hydroxylation of fluorene. Several mono- and dihydroxy products and ring-cleavage products were identified for phenanthrene, fluoranthene and anthracene. It appeared that the cometabolism of those three compounds is a non-specific process, in contrast to the metabolism of fluorene. For dibenzothiophene the metabolites dibenzothiophene-5-oxide and dibenzothiophene-5,5-dioxide were identified; these compounds appeared to be the products of a dead-end pathway. Since apart from dibenzothiophene no metabolites were found in very high concentrations for any of the other substrates, complete degradation is suggested, even for the cometabolic degradation of phenanthrene, fluoranthene and anthracene.

Plastics in the Marine Environment: The Dark Side of a Modern Gift

Plastics are cheap, strong, and durable and offer considerable benefits to humanity. They potentially can enhance the benefits that both medical and scientific technology will bestow to humankind. However, it has now been several decades since the use of plastics exploded, and we have evidence that our current approach to production, use, transport and disposal of plastic materials has caused, and is still causing serious effects on wildlife, and is not sustainable. Because of frequent inappropriate waste management practices, or irresponsible human behavior, large masses of plastic items have been released into the environment, and thereby have entered the worlds oceans. Moreover, this process continues, and in some places is even increasing. Most plastic debris that now exists in the marine environment originated from ocean-based sources such as the fishing industry. Plastics accumulate in coastal areas, at the ocean surface and on the seabed. Because 70% of all plastics are known to eventually sink, it is suspected that ever increasing amounts of plastic items are accumulating in seabed sediments. Plastics do not biodegrade, although, under the influence of solar UV radiations, plastics do degrade and fragment into small particles, termed microplastics. Our oceans eventually serve as a sink for these small plastic particles and in one estimate, it is thought that 200,000 microplastics per km(2) of the oceans surface commonly exist. The impact of plastic debris has been studied since the beginning of the 1960s. To date, more than 267 species in the marine environment are known to have been affected by plastic entanglement or ingestion. Marine mammals are among those species that are most affected by entanglement in plastic debris. By contrast, marine birds suffer the most from ingestion of plastics. Organisms can also be seriously absorbed by floating plastic debris, or the contaminants may derive from plastic additives that are leached to the environment. Recent studies emphasize the important role of microplastics as they are easily ingestible by small organisms, such as plankton species, and form a pathway for contaminants to enter the food web. Contaminants leached from plastics tend to bioaccumulate in those organisms that absorb them, and chemical concentrations are often higher at higher trophic levels. This causes a threat to the basis of every food web and can have serious and far-reaching effects, even on nonmarine species such as polar bears and humans, who consume marine-grown food. Therefore, resolving the plastic debris problem is important to human kind for two reasons: we are both creator, and victim of the plastic pollution problem. Solutions to the plastic debris problem can only be achieved through a combination of actions. Such actions include the following: Legislation against marine pollution by plastics must be enforced, recycling must be accentuated, alternatives (biodegradable) to current plastic products must be found, and clean-up of debris must proceed, if the marine plastic pollution problem is to eventually be resolved. Governments cannot accomplish this task on their own, and will need help and initiative from the public. Moreover, resolving this long-standing problem will require time, money, and energy from many individuals now living and those of future generations, if a safer and cleaner marine environment is to be achieved.

Degradation of anthracene by Mycobacterium sp. strain LB501T proceeds via a novel pathway, through o-phthalic acid.

ABSTRACT Mycobacterium sp. strain LB501T utilizes anthracene as a sole carbon and energy source. We analyzed cultures of the wild-type strain and of UV-generated mutants impaired in anthracene utilization for metabolites to determine the anthracene degradation pathway. Identification of metabolites by comparison with authentic standards and transient accumulation of o-phthalic acid by the wild-type strain during growth on anthracene suggest a pathway through o-phthalic acid and protocatechuic acid. As the only productive degradation pathway known so far for anthracene proceeds through 2,3-dihydroxynaphthalene and the naphthalene degradation pathway to form salicylate, this indicates the existence of a novel anthracene catabolic pathway in Mycobacterium sp. LB501T.

From Bioavailability Science to Regulation of Organic Chemicals

The bioavailability of organic chemicals in soil and sediment is an important area of scientific investigation for environmental scientists, although this area of study remains only partially recognized by regulators and industries working in the environmental sector. Regulators have recently started to consider bioavailability within retrospective risk assessment frameworks for organic chemicals; by doing so, realistic decision-making with regard to polluted environments can be achieved, rather than relying on the traditional approach of using total-extractable concentrations. However, implementation remains difficult because scientific developments on bioavailability are not always translated into ready-to-use approaches for regulators. Similarly, bioavailability remains largely unexplored within prospective regulatory frameworks that address the approval and regulation of organic chemicals. This article discusses bioavailability concepts and methods, as well as possible pathways for the implementation of bioavailability into risk assessment and regulation; in addition, this article offers a simple, pragmatic and justifiable approach for use within retrospective and prospective risk assessment.

Updated Abraham Solvation Parameters for Polychlorinated Biphenyls

This study shows that the recently published polychlorinated biphenyl (PCB) Abraham solvation parameters predict PCB air-n-hexadecane and n-octanol-water partition coefficients very poorly, especially for highly ortho-chlorinated congeners. Therefore, an updated set of PCB solvation parameters was derived from four PCB properties and associated Abraham solvation equations. Additionally, the influence of ortho-chlorination on PCB solvent accessible volume and surface area was investigated. The updated PCB solvation parameters were tested on partitioning between five other phase combinations. Compared to the original PCB solvation parameter set, the updated PCB solvation parameters resulted in substantially improved estimates from Abraham solvation equations for (subcooled) liquid vapor pressures, aqueous solubilities, HPLC capacity factors, and for coefficients of air-n-hexadecane, air-water, organic carbon-water, and n-octanol-water partitioning. For water to polydimethyl siloxane and sodium dodecylsulphate (SDS) partitioning, the updated PCB solvation parameters yielded no improvement compared to the original data set. The main difference between the updated and the original parameter set is that updated PCB McGowan specific volumes depend on the degree of ortho-chlorination, which is qualitatively confirmed by trends in the PCB solvent accessible volumes and surface areas. The use of the updated PCB solvation parameters instead of the original values is therefore recommended.

Enhanced kinetics of solid-phase microextraction and biodegradation of polycyclic aromatic hydrocarbons in the presence of dissolved organic matter†

The uptake kinetics of fluorene, phenanthrene, fluoranthene, pyrene, and benzo[e]pyrene by solid-phase microextraction fibers was studied in the presence of dissolved organic matter (DOM) obtained from sediment pore water and resulted in increased fiber absorption and desorption rate coefficients. Compared to the control without DOM, these rate coefficients were increased at a DOM concentration of 36.62 mg/L by a factor of 1.27 to 2.21 and 1.31 to 2.10 for fluorene and benzo[e]pyrene, respectively. The calculated values for the fiber absorption and desorption rate coefficients show that diffusion through an unstirred boundary layer (UBL) surrounding the fiber probably forms the rate-limiting step of the process. The mineralization of aqueous-phase phenanthrene and pyrene by a representative polycyclic aromatic hydrocarbon (PAH)-degrading bacterium (Mycobacterium gilvum VM552) also was found to be enhanced by DOM. The initial degradation rates of phenanthrene (9.03 μg/L) and pyrene (1.96 μg/L) were significantly higher compared to the control values and were enhanced by a factor of 1.32 and 1.26 at a DOM concentration of 43.14 and 42.15 mg/L, respectively. We suggest that such an enhancement results from the combination of faster uptake kinetics of the water-dissolved compounds in the UBL surrounding microbial cells and direct access of the bacteria to DOM-associated PAHs. These enhanced kinetic effects of DOM may have strong implications in sediment processes like desorption, nonequilibrium exposure, and biodegradation.

Biodegradation of chlorinated biphenyls and benzoic acids by a Pseudomonas strain

SummaryA Pseudomonas strain able to grown on biphenyl and 2- and 4-chlorobiphenyl has been isolated from soil. Benzoate-grown cultures of this strain were able to cometabolize other chlorobiphenyls to the corresponding chlorobenzoates. In contrast to most of the chlorobiphenyl-degrading strains described previously in the literature, which are reported to form chlorobenzoates as end metabolites from chlorobiphenyls, this strain is also able to further cometabolize chlorobenzoates to form ring-cleaved compounds.

Persistence, Bioaccumulation, and Toxicity of Halogen-Free Flame Retardants

Polymers are synthetic organic materials having a high carbon and hydrogen content, which make them readily combustible. Polymers have many indoor uses and their flammability makes them a fire hazard. Therefore, flame retardants (FRs) are incorporated into these materials as a safety measure. Brominated flame retardants (BFRs), which accounted for about 21% of the total world market of FRs, have several unintended negative effects on the environment and human health. Hence, there is growing interest in finding appropriate alternative halogen-free flame retardants (HFFRs). Many of these HFFRs are marketed already, although their environ- mental behavior and toxicological properties are often only known to a limited extent, and their potential impact on the environment cannot yet be properly assessed. Therefore, we undertook this review to make an inventory of the available data that exists (up to September 2011) on the physical-chemical properties, pro- duction volumes, persistence, bioaccumulation, and toxicity (PBT) of a selection of HFFRs that are potential replacements for BFRs in polymers. Large data gaps were identified for the physical-chemical and the PBT properties of the reviewed HFFRs. Because these HFFRs are currently on the market, there is an urgent need to fill these data gaps. Enhanced transparency of methodology and data are needed to reevaluate certain test results that appear contradictory, and, if this does not provide new insights, further research should be performed. TPP has been studied quite extensively and it is clearly persistent, bioaccumulative, and toxic. So far, RDP and BDP have demonstrated low to high ecotoxicity and persistence. The compounds ATH and ZB exerted high toxicity to some species and ALPI appeared to be persistent and has low to moderate reported ecotoxicity. DOPO and MPP may be persistent, but this view is based merely on one or two studies, clearly indicating a lack of information. Many degradation studies have been performed on PER and show low persistence, with a few exceptions. Additionally, there is too l ittle information on the bioaccumulation potential of PER. APP mostly has low PBT properties; however, moderate ecotoxicity was reported in two studies. Mg(OH)₂, ZHS, and ZS do not show such remarkably high bioaccumulation or toxicity, but large data gaps exist for these compounds also. Nevertheless, we consider the latter compounds to be the most promising among alternative HFFRs. To assess whether the presently reviewed HFFRs are truly suitable alternatives, each compound should be examined individually by comparing its PBT values with those of the relevant halogenated flame retardant. Until more data are available, it remains impossible to accurately evaluate the risk of each of these compounds, including the ones that are already extensively marketed.