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A Systematic Evaluation of Dissolved Lead Sorption Losses to Syringe Filter Materials
Citation:
Minning, T., D. Lytle, AND M. Pham. A Systematic Evaluation of Dissolved Lead Sorption Losses to Syringe Filter Materials. Presented at AWWA ACE13 Annual Conference & Exposition, Denver, CO, June 09 - 13, 2013.
Impact/Purpose:
The objective of this work was to systematically examine the tendency of syringe filter materials to sorb lead. Specifically, seventeen 0.45 µm pore size, 25 mm syringe filters of many common types and brands were examined. Sorption of completely soluble lead and copper (with a focus on lead) at a controlled flow rate and sample throughput was quantified. The outcome of the work is to determine the best filter material for filtration of water samples containing trace metals and to develop a general method in determining soluble/particulate fractions of lead and copper in water samples.
Description:
Lead poses a great health risk and, as a result, reducing lead levels at consumer’s taps is a goal of water utilities. Identifying whether soluble or particulate lead is present in water is useful in understanding the mechanism of lead release and identifying a remedial strategy. Typically soluble lead is defined as the lead that passes a 0.45 µm filter and particulate lead is the fraction that is removed by the filter. Syringe filters are commonly used in the field and laboratory. Unfortunately there is very little guidance in the method regarding the filter membrane material, method of filtration (or if filtration by syringe is equivalent to filtration by peristaltic pump if only small amounts of sample need to be processed), sample size, or membrane surface area. There is also very little discussion of the possibility of the sorption of dissolved trace metals to the filter itself and whether filter parameters listed above impact sorption tendencies of metals to the filter. The objective of this work was to systematically examine the tendency of syringe filter materials to sorb lead. Specifically, seventeen 0.45 µm pore size, 25 mm syringe filters of many common types and brands were examined. Sorption of completely soluble lead and copper (with a focus on lead) at a controlled flow rate and sample throughput was quantified. The outcome of the work is to determine the best filter material for filtration of water samples containing trace metals and to develop a general method in determining soluble/particulate fractions of lead and copper in water samples. An aqueous solution of 50 µg/L soluble lead was prepared at pH 7 and buffered with 50 mg C/L DIC using sodium bicarbonate. A large syringe and syringe pump were used to pass six consecutive 15 mL volumes of lead-containing water through the filter in question into conical vials for analysis by ICP-MS. A constant rate of 50 mL/min was chosen for testing. Samples were taken directly from the vessel and from the syringe before and after the filter assessment as control values. This process was repeated for solutions of 20 µg/L lead in addition to two solutions containing 100 ug/L lead & 0.75 mg/L copper and 50 µg/L lead & 100 mg/L calcium. Testing was done in triplicate. Amounts of lead sorbed greatly varied by filter. The Nylon with GMF prefilter removed an average of 99.6% of lead from the water, while a mixed cellulose ester filter removed an average of 5% and a polyethersulfone filter removed an average of 6% over the course of the 90 mL sampling. A commonly used Nylon membrane removed 17% of soluble lead. Many filters showed a trend of large amounts of lead sorbed in the first 15-30 mL passed, with losses decreasing as volume passed reached the 90 mL mark. The results show that great care must be taken in choosing a filter when filtering soluble lead. With such a variance in lead sorption between membranes and increased sorption when filtering small samples, there is a great possibility of biased results leading to misinterpretation of the data.
URLs/Downloads:
http://www.awwa.org/portals/0/files/education/conferences/ace/conference-program/resources/index.htm