Membrane assisted passive sampler for aquatic organic chemicals: characterization of environmental conditions and field performance

Nyoni, Hlengilizwe
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Membrane assisted passive sampler (MAPS) is an informative, cost-effective and environmentally friendly approach for monitoring of ionisable organic compounds in water bodies. The sampler uses no organic solvent. By adjusting the pH of the acceptor phase, both acidic chlorophenols and basic triazine model compounds were extracted. The sampler was optimized under laboratory conditions followed by field applications on the same compounds. The optimised parameters were temperature of the water body, turbulence, protective cover, biofouling, matrix effects such as humic substances, degree of trapping in the acceptor phase and exposure time. It was found that the sampling kinetics of most of the tested analytes are dependent on temperature and on the hydrodynamic conditions. Also, a strong dependence of the sampling rates reduction on sample matrix and protective cover used was noted. The chemical uptake of both the acidic chlorophenols and basic triazine compounds into the passive sampler remained linear and integrative through out the exposure periods. The amounts quantified in the MAPS had relative standard deviations mostly between 10 % and 20 % (from repeat determinations) and did in no case exceed 30 %. The behaviour of the MAPS to monitor ionisable triazine compounds in dam water of the Hartebeespoort was compared to Chemcatcher and solid phase extraction technique with C18 sorbents of spot samples. Similarly, the behaviour of the MAPS to monitor ionisable chlorophenol compounds in wastewater of the Goudkoppies Wastewater Treatment Plant was compared to solid phase extraction technique. There were no triazine and chlorophenol compounds detected in any of the deployed passive samplers in the field applications. The same results were obtained in grab samples extracted with solid phase extraction under laboratory conditions. However, data from laboratory studies support the feasibility of MAPS to measure the freely dissolved fraction of ionisable organic chemicals in water. Using water from the Hartebeespoort dam spiked with 50 μg L-1 triazine, the detection limits of triazine compounds ranged from 11.38 to 61.86 μg L-1 for direct injection, 1.082 to 23.077 μg L-1 for MAPS, 0.892 to 5.769 μg L-1 for Chemcatcher and 1.482 to 7.410 μg L-1 for SPE. While using water from Goudkoppies Wastewater Treatment Plant spiked with 100 μg L-1 chlorophenols, the detection limits of the passive sampler were comparable with that of solid phase extraction and were around 1.5 μg L-1. Estimation and interpretation of enrichment factors in the passive samplers and SPE were generally comparable ranging from 46 to 295 for chlorophenol compounds. Also, for triazine compounds, the obtained enrichment factors in the passive samplers and SPE are generally comparable with the exception of enrichment factors of propazine, ametryn terbuthylazine, prometryn and terbutryn compounds which were higher for the MAPS ranging from 46 to 65.
Water montoring, passive sampling, MAPS, Environmental factors, Chlorophenol, Triazines, HPLC/UV