The seasonality of chemical persistence in a Swedish lake by benchmarking
Chemicals with high persistence (i.e. long degradation half-lives) could pose high risks to living organisms and humans and be subject to long-range transport. It is challenging to measure persistence directly in the field due to lack of appropriate methods. Chemical benchmarking as an alternative method was evaluated to have potential to assess the persistence in real aquatic environment . It has been further applied in a Swedish lake (Norra Bergundasjön) for measuring the persistence of a group of pharmaceuticals and compared (and validated) with traditional mass balance approach . The degradation of a chemical in a lake could be influenced by several factors including temperature, sunlight, pH and nature of the degrading microorganisms, which may vary in time and space. So in this study benchmarking was used to study the temporal variation of persistence of 7 pharmaceuticals in another Swedish lake (Boren) that receives the discharge from a WWTP and inflowing water from Vättern. The sampling campaigns were conducted in late spring, late autumn and winter of 2013. Acesulfame K (an artificial sweetener) was used as the benchmark chemical. The results show that the strongest seasonal variability was between spring and autumn. The half-lives of 5 chemicals in spring were shorter than in autumn, mainly because of lower temperature and weak irradiation in autumn. The half-lives of chemicals in Boren were also compared with that in Norra Bergundasjön. This could be explained by the difference in the nutrient status and pH in these two Swedish lakes. Benchmarking did open a new door to measure persistence in a broader range than before and more opportunities to study the spatial and temporal variability of persistence in the real environment.
Identifying Chemicals That Are Planetary Boundary Threats
Rockström et al. proposed a set of planetary boundaries that delimit a “safe operating space for humanity”. Many of the planetary boundaries that have so far been identified are determined by chemical agents. Other chemical pollution-related planetary boundaries likely exist, but are currently unknown. A chemical poses an unknown planetary boundary threat if it simultaneously fulfills three conditions: (1) it has an unknown disruptive effect on a vital Earth system process; (2) the disruptive effect is not discovered until it is a problem at the global scale, and (3) the effect is not readily reversible. In this paper, we outline scenarios in which chemicals could fulfill each of the three conditions, then use the scenarios as the basis to define chemical profiles that fit each scenario. The chemical profiles are defined in terms of the nature of the effect of the chemical and the nature of exposure of the environment to the chemical. Prioritization of chemicals in commerce against some of the profiles appears feasible, but there are considerable uncertainties and scientific challenges that must be addressed. Most challenging is prioritizing chemicals for their potential to have a currently unknown effect on a vital Earth system process. We conclude that the most effective strategy currently available to identify chemicals that are planetary boundary threats is prioritization against profiles defined in terms of environmental exposure combined with monitoring and study of the biogeochemical processes that underlie vital Earth system processes to identify currently unknown disruptive effects.
Identifying chemicals that are planetary boundary threats.
Evaluation of the potential of benchmarking to facilitate the measurement of chemical persistence in lakes
The persistence of chemicals in the environment is rarely measured in the field due to a paucity of suitable
methods. Here we explore the potential of chemical benchmarking to facilitate the measurement of
persistence in lake systems using a multimedia chemical fate model. The model results show that persistence
in a lake can be assessed by quantifying the ratio of test chemical and benchmark chemical at as
few as two locations: the point of emission and the outlet of the lake. Appropriate selection of benchmark
chemicals also allows pseudo-first-order rate constants for physical removal processes such as volatilization
and sediment burial to be quantified. We use the model to explore how the maximum persistence
that can be measured in a particular lake depends on the partitioning properties of the test chemical
of interest and the characteristics of the lake. Our model experiments demonstrate that combining
benchmarking techniques with good experimental design and sensitive environmental analytical chemistry
may open new opportunities for quantifying chemical persistence, particularly for relatively slowly
degradable chemicals for which current methods do not perform well.
Chemical benchmarking to determine the persistence of pharmaceuticals in a Swedish lake.
Silicone passive equilibrium samplers as ‘chemometers’ in eels and sediments of a Swedish lake
Passive equilibrium samplers deployed in two or more media of a system and allowed to come to equilibrium can be viewed as ‘chemometers’ that reflect the difference in chemical activities of contaminants between the media. We applied silicone-based equilibrium samplers to measure relative chemical activities of seven ‘indicator’ polychlorinated biphenyls (PCBs) and hexachlorobenzene in eels and sediments from a Swedish lake. Chemical concentrations in eels and sediments were also measured using exhaustive extraction methods. Lipid-normalized concentrations in eels were higher than organic carbon-normalized concentrations in sediments, with biota–sediment accumulation factors (BSAFs) of five PCBs ranging from 2.7 to 12.7. In contrast, chemical activities of the same pollutants inferred by passive sampling were 3.5 to 31.3 times lower in eels than in sediments. The apparent contradiction between BSAFs and activity ratios is consistent with the sorptive capacity of lipids exceeding that of sediment organic carbon from this ecosystem by up to 50-fold. Factors that may contribute to the elevated activity in sediments are discussed, including slower response of sediments than water to reduced emissions, sediment diagenesis and sorption to phytoplankton. The ‘chemometer’ approach has the potential to become a powerful tool to study the thermodynamic controls on persistent organic chemicals in the environment and should be extended to other environmental compartments.