Calibration of a passive sampler based on stir bar sorptive extraction for the monitoring of hydrophobic organic pollutants in water

Prediction of the accumulation behavior of pesticides in PDMS-coated stir bars used as passive samplers in freshwaters

Passive samplers accumulate organic contaminants at rates that depend on in-field exposure conditions such as freshwater flow velocity, water temperature and water quality. Time-weighted average concentrations can be determined by using a correction process such as the performance reference compound (PRC) method. This study presented a new approach to predict the accumulation behavior of pesticides in polydimethylsiloxane-coated stir bars under different exposure conditions and assign a specific PRC to each pesticide for quantitative purposes. We used an experimental design with eight simultaneous accumulation kinetics of 13 pesticides and elimination kinetics of three PRC candidates run in a flow-through system to determine the effects of flow velocity, water temperature and dissolved organic matter on the kinetic constants. We identified the parameters that had a significant effect on the accumulation of each pesticide and assigned a PRC candidate to each pesticide. We then used a discriminant function analysis to find the parameters that had a significant effect on accumulation of the 13 pesticides via their physical-chemical properties and to predict through a stochastic approach the parameters for seven other pesticides. This approach provides a better framework for identifying a PRC than conventional methods to determine unbiased concentrations in future monitoring efforts.

Examining the applicability of polar organic chemical integrative sampler for long-term monitoring of groundwater contamination caused by currently used pesticides

The possibilities of expanding a groundwater quality monitoring scheme by passive sampling using polar organic chemical integrative sampler (POCIS) comprising HLB sorbent as the receiving phase were explored. Passive sampling and grab sampling were carried out simultaneously in the regions with vulnerable groundwater resources in Slovakia, between 2013 and 2021. For 27 pesticides and degradation products detected both in POCIS and the grab samples, in situ sampling rates were calculated and statistically evaluated. The limited effectiveness of the receiving phase in POCIS for sampling polar or ionized compounds was confirmed through a comparison of the medians of compound-specific sampling rates. For the majority of the monitored compounds the median sampling rates varied between 0.01 and 0.035 L/day. In some cases, the actual in situ values could be confirmed by parallel exposure of POCIS and silicone rubber sheet employed to obtain a benchmark for maximum attainable sampling rate. Sampling site and sampling period appear to have also some influence on the sampling rates, which was attributed in part to the groundwater velocity varying in both space and time. The influence of physico-chemical parameters (temperature, pH, electrolytic conductivity) remains mostly questionable due to the naturally limited ranges of recorded values over the entire duration of the study. Concentrations of pollutants in POCIS could be used for predicting time weighed average concentrations in water, provided the sampling rates were known and relatively constant. Generally, the compound-specific sampling rate cannot be considered constant due to a combination of naturally varying environmental factors that influence the actual in situ sampling rate. The relative standard deviation of concentration data from POCIS exposed in triplicates varied between approx. 5 %-50 %. Utilizing exploratory data analysis approach and tools enabled us to obtain a relatively complex picture of the situation and progress regarding pesticide pollution of groundwater in the monitored areas.

Performance comparison of silicone and low-density polyethylene as passive samplers in a global monitoring network for aquatic organic contaminants

Contamination with hydrophobic organic compounds (HOCs) such as persistent organic pollutants negatively affects global water quality. Accurate and globally comparable monitoring data are required to understand better the HOCs distribution and environmental fate. We present the first results of a proof-of-concept global monitoring campaign, the Aquatic Global Passive Sampling initiative (AQUA-GAPS), performed between 2016 and 2020, for assessing trends of freely dissolved HOC concentrations in global surface waters. One of the pilot campaign aims was to compare performance characteristics of silicone (SSP) and low-density polyethylene (PE) sheets co-deployed in parallel under identical conditions, i.e. at the same site, using the same deployment design, and for an equal period. Individual exposures lasted between 36 and 400 days, and samples were collected from 22 freshwater and 40 marine locations. The sampler inter-comparability is based on a rationale of common underlying principles, i.e. HOC diffusion through a water boundary layer (WBL) and absorption by the polymer. In the integrative uptake phase, equal surface-specific uptake in both samplers was observed for HOCs with a molecular volume less than 300 Å³. For those HOCs, transport in the WBL controls the uptake as mass transfer in the polymer is over 20-times faster. In such a case, sampled HOC mass can be converted into aqueous concentrations using available models derived for WBL-controlled sampling using performance reference compounds. In contrast, for larger molecules, surface-specific uptake to PE was lower than to SSP. Diffusion in PE is slower than in SSP, and it is likely that for large molecules, diffusion in PE limits the transport from water to the sampler, complicating the interpretation. Although both samplers provided mostly well comparable results, we recommend, based on simpler practical handling, simpler data interpretation, and better availability of reliable polymer-water partition coefficients, silicone-based samplers for future operation in the worldwide monitoring programme.

Development and application of an in-house library and workflow for gas chromatography-electron ionization-accurate-mass/high-resolution mass spectrometry screening of environmental samples

This work presents an optimized gas chromatography–electron ionization–high-resolution mass spectrometry (GC-EI-HRMS) screening method. Different method parameters affecting data processing with the Agilent Unknowns Analysis SureMass deconvolution software were optimized in order to achieve the best compromise between false positives and false negatives. To this end, an accurate-mass library of 26 model compounds was created. Then, five replicates of mussel extracts were spiked with a mixture of these 26 compounds at two concentration levels (10 and 100 ng/g dry weight in mussel, 50 and 500 ng/mL in extract) and injected in the GC-EI-HRMS system. The results of these experiments showed that accurate mass tolerance and pure weight factor (combination of reverse-forward library search) are the most critical factors. The validation of the developed method afforded screening detection limits in the 2.5–5 ng range for passive sampler extracts and 1–2 ng/g for mussel sample extracts, and limits of quantification in the 0.6–3.2 ng and 0.1–1.8 ng/g range, for the same type of samples, respectively, for 17 model analytes. Once the method was optimized, an accurate-mass HRMS library, containing retention indexes, with ca. 355 spectra of derivatized and non-derivatized compounds was generated. This library (freely available at https://doi.org/10.5281/zenodo.5647960), together with a modified Agilent Pesticides Library of over 800 compounds, was applied to the screening of passive samplers, both of polydimethylsiloxane and polar chemical integrative samplers (POCIS), and mussel samples collected in Galicia (NW Spain), where a total of 75 chemicals could be identified.

Mechanistic insight on transfer rate of the polar organic compounds through the polyethersulfone membrane

Polar Organic Chemical Integrative Samplers (POCIS) with two supporting polyethersulfone (PES) membranes and a strong adsorbent in between are frequently used to determine the concentrations of polar organic contaminants in the aqueous environment. The solute transfer rate (SRs) through PES is a key parameter affecting the critical membrane/water partitioning coefficient (R_mw) of polar organic molecules, which in turn affects the concentration of these molecules on the adsorbent and the accuracy of POCIS measurement. However, information on SRs and R_mw in the literature is very limited. Prolonged use of POCIS in the measurement of organic compounds may lead to membrane fouling by the retained organic compounds. The relationship between the properties of the polar organic compounds and their different accumulation behaviors in POCIS is not yet clear. This study aimed to measuring the solute transfer rate of four polar organic compounds (atrazine, caffeine, ibuprofen, and atenolol). The results indicated that atrazine had the highest SR of 0.49 mL day^-1. Both caffeine and atenolol had an SRs of approximately 0.3 mL day^-1. Ibuprofen had the lowest SR of 0.23 mL day^-1. The results further revealed that the tendency of the organic solutes to adsorb onto interstitial spaces of the PES polymer was associated with their hydrophobicity and molecular structures.

An improved design of a passive sampler for polar organic compounds based on diffusion in agarose hydrogel

Passive samplers based on diffusive gradients in thin hydrogel films (DGT) were recently modified for sampling of polar organic compounds in water. However, since the sampling rates of the commonly used DGT design with the surface area of 3.1 cm² are low, we propose to increase them by applying a two-sided design with a larger sampling surface area of 22.7 cm². The sampler design consists of two sorptive hydrogel disks compressed between two diffusive hydrogel disk layers strengthened by nylon netting and held together by two stainless steel rings. Sorbent/water distribution coefficients (K_SW) were determined, and the sampler was calibrated for monitoring 11 perfluoroalkyl substances and 12 pharmaceuticals and personal care products in water at laboratory conditions using a closed system with artificial flow generated by submersible pumps. A field performance test was conducted at five locations in the Morava River basin in Czech Republic. The median value of laboratory-derived sampling rates was 43 mL day^-1 with extreme values of 2 mL day^-1 and 90 mL day^-1 for perfluorotridecanoic and perfluoroheptanoic acids, respectively. The log K_SW values of tested compounds ranged from 3.18 to 5.47 L kg^-1, and the estimated halftime to attain sampler-water equilibrium ranged from 2 days to more than 28 days, which is the maximum recommended exposure period, considering potential issues with the stability of hydrogel. The sampler can be used for assessment of spatial trends as well as estimation of aqueous concentration of investigated polar compounds.

Application of triolein-embedded cellulose acetate membrane (TECAM) passive sampler to study phase distribution of hexabromocyclododecanes (HBCDs) in sediment

Hexabromocyclododecanes (HBCDs) are a class of widely used brominated flame retardants (BFRs) that exhibit strong hydrophobicity. The ubiquity and persistence of HBCDs in sediment have attracted significant attention because of public health concerns. The environmental fate and ecological risks of HBCDs closely depend on their phase distribution in sediments. However, little information is available regarding the freely dissolved concentrations (C_free) of HBCDs in sediment porewater. In this study, we developed a method to measure C_free of HBCDs in sediment porewater using triolein-embedded cellulose acetate membranes (TECAM). The TECAM-to-water partitioning coefficient (log K_TECAM) was 4.69, 4.77, and 4.63 for α-HBCD, β-HBCD, and γ-HBCD, respectively. In sediments, HBCDs sorbed to the sediment solid phase accounted for more than 99% of the total chemical mass. The dissolved organic carbon (DOC)-water partition coefficient (K_DOC) values were derived from TECAM measurements, and the log K_DOC values ranged from 5.77 to 6.23 for the three HBCD diastereomers, suggesting a strong tendency for HBCDs to sorb to DOC. The high sorption of HBDCs for DOC implies a potential for DOC-facilitated transport which may enhance the environmental mobility of HBCDs.

Calibration of silicone rubber rods as passive samplers for pesticides at two different flow velocities: Modeling of sampling rates under water boundary layer and polymer control

There is a need to determine time-weighted average concentrations of polar contaminants such as pesticides by passive sampling in environmental waters. Calibration data for silicone rubber-based passive samplers are lacking for this class of compounds. The calibration data, sampling rate (R_s ), and partition coefficient between silicone rubber and water (K_sw ) were precisely determined for 23 pesticides and 13 candidate performance reference compounds (PRCs) in a laboratory calibration system over 14 d for 2 water flow velocities, 5 and 20 cm s^-1 . The results showed that an in situ exposure duration of 7 d left a silicone rubber rod passive sampler configuration in the linear or curvilinear uptake period for 19 of the pesticides studied. A change in the transport mechanism from polymer control to water boundary layer control was observed for pesticides with a log K_sw of approximately 3.3. The PRC candidates were not fully relevant to correct the impact of water flow velocity on R_s . We therefore propose an alternative method based on an overall resistance to mass transfer model to adjust R_s from laboratory experiments to in situ hydrodynamic conditions. We estimated diffusion coefficients (D_s ) and thickness of water boundary layer (δ_w ) as adjustable model parameters. Log D_s values ranged from -12.13 to -10.07 m²  s^-1 . The estimated δ_w value showed a power function correlation with water flow velocity. Environ Toxicol Chem 2018;37:1208-1218. © 2017 SETAC.

Applicability of polydimethylsiloxane (PDMS) and polyethersulfone (PES) as passive samplers of more hydrophobic organic compounds in intertidal estuarine environments

The uptake calibration of three passive samplers, stir-bars, MESCO/stir-bars and polyethersulfone tubes (PES_t), was assessed in seawater at different salinities for 17 organic compounds including organochlorine compounds, pesticides, phthalates, musk fragrances and triclosan. The calibration procedure was accomplished by exposing the samplers to a continuous flow of fortified seawater for up to 14days under laboratory conditions. Prior to the exposure, stir-bars and MESCO/stir-bars were loaded with a known amount of deuterated PAH mixture as performance reference compounds (PRC). For most of the studied compounds, the sampling rates (Rs, mL·day^-1) were determined for each sampler at two salinities (15 and 30‰) and two nominal concentrations (25 and 50ng·L^-1). Among the tested devices, though PES can be an outstanding cheap alternative to other passive samplers, naked or free stir-bars provided the best results in terms of uptake rates (i.e., the Rs values ranged from 30 to 350mL·day^-1). Regarding the variation of the salinity, the Rs values obtained with naked stir-bars were statistically comparable in the full range of salinities (0-30‰) but the values obtained with MESCO/stir-bars and PES_t were salinity dependent. Consequently, only stir-bars assured the required robustness to be used as passive samplers in intertidal estuarine environments. Finally, the stir-bars were applied to estimate the time-weighted average concentration of some of those contaminants in the feeding seawater of the experimental aquaria at the Plentzia Marine Station (Basque Country) and low levels of musks fragrances (0.1-0.2ng·L^-1) were estimated.

An expanded conceptual framework for solution-focused management of chemical pollution in European waters

BACKGROUND

This paper describes a conceptual framework for solutions-focused management of chemical contaminants built on novel and systematic approaches for identifying, quantifying and reducing risks of these substances.

METHODS

The conceptual framework was developed in interaction with stakeholders representing relevant authorities and organisations responsible for managing environmental quality of water bodies. Stakeholder needs were compiled via a survey and dialogue. The content of the conceptual framework was thereafter developed with inputs from relevant scientific disciplines.

RESULTS

The conceptual framework consists of four access points: Chemicals, Environment, Abatement and Society, representing different aspects and approaches to engaging in the issue of chemical contamination of surface waters. It widens the scope for assessment and management of chemicals in comparison to a traditional (mostly) perchemical risk assessment approaches by including abatement- and societal approaches as optional solutions. The solution-focused approach implies an identification of abatement- and policy options upfront in the risk assessment process. The conceptual framework was designed for use in current and future chemical pollution assessments for the aquatic environment, including the specific challenges encountered in prioritising individual chemicals and mixtures, and is applicable for the development of approaches for safe chemical management in a broader sense. The four access points of the conceptual framework are interlinked by four key topics representing the main scientific challenges that need to be addressed, i.e.: identifying and prioritising hazardous chemicals at different scales; selecting relevant and efficient abatement options; providing regulatory support for chemicals management; predicting and prioritising future chemical risks. The conceptual framework aligns current challenges in the safe production and use of chemicals. The current state of knowledge and implementation of these challenges is described.

CONCLUSIONS

The use of the conceptual framework, and addressing the challenges, is intended to support: (1) forwarding sustainable use of chemicals, (2) identification of pollutants of priority concern for cost-effective management, (3) the selection of optimal abatement options and (4) the development and use of optimised legal and policy instruments.