Membrane assisted passive sampler for triazine compounds in water bodies—Characterization of environmental conditions and field performance

摘要

In this work, a simple, inexpensive and very selective membrane assisted passive sampler (MAPS) that does not use organic solvents, based on a thin walled silicone hollow fibre membrane for extraction of ionizable organic compounds in water bodies is reported. The potential for passive sampling of basic compounds is demonstrated. By changing the acceptor solution from acidic to basic conditions, the MAPS can be successfully used to extract acidic organic compound. The influence of environmental factors such as temperature, sample matrix and hydrodynamics on enrichment factors and sampling rates have been investigated in order to calibrate the passive sampler for measurement of TWA concentration of triazines. The selectivity, extraction efficiency and enrichment factor of the developed sampler has been compared to the Chemcatcher passive sampler. It was found that the chemical uptake of basic triazine compounds into the passive sampler remained linear and integrative throughout the 7 days exposure periods. For atrazine, propazine, prometryne and terbutryne a large 3 days time lag was experienced. A plot of natural logarithms of the amount taken up by the sampler against exposure time gave linear relationship for these compounds. The sampling rates for individual triazine compounds increased with change of hydrodynamic conditions from static to turbulent. The presence of 20 mg L~(-1) humic substances in solution was found to have no significant effect on the concentration of compounds trapped in the acceptor solution. Once these compounds are trapped in the acceptor solution they do not diffuse back during the deployment period. A strong dependence of the sampling rates on the type of protective cover used was noted. Stainless steel protective cover was found to be the better than the iron mesh as it did not rust during deployment. The detection limits on HPLC with UV detection ranged from 0.50 to 4.50 μg L~(-1) for MAPS, 0.40 to 3.50 μg L~(-1) for Chemcatcher passive sampler and 0.35 to 4.50 μg L~(-1) for SPE with 7 days exposure of passive samplers. Preliminary field trial of the potential of the MAPS to monitor ionizable triazine compounds in Hartebeespoort dam found west of Johannesburg, South Africa was compared to Chemcatcher and SPE technique with C_(18) sorbents for grab samples. No quantifiable amounts of triazine compounds were found in any of the deployed passive samplers in the preliminary field applications. Triazine compounds were also not detected in grab samples after SPE. However, data from laboratory studies support the feasibility of MAPS to measure the freely dissolved fraction of ionizable organic chemicals in water. The MAPS also exhibited slightly better selectivity towards matrix components found in natural water compared to SPE technique or Chemcatcher with C_(18) disk as trapping media.