Point-of-Use Filters for Lead Removal from Tap Water: Opportunities and Challenges

Characterization of Fe-Containing and Pb-Containing Nanoparticles Resulting from Corrosion of Plumbing Materials in Tap Water Using a Hyphenated ATM-DMA-spICP-MS System

Single-particle inductively coupled plasma mass spectrometry (spICP-MS) has been used to characterize metallic nanoparticles (NPs) assuming that all NPs are spherical and composed of pure element. However, environmental NPs generally do not meet these criteria, suggesting that spICP-MS may underestimate their true sizes. This study employed a system hyphenating the atomizer (ATM), differential mobility analyzer (DMA), and spICP-MS to characterize metallic NPs in tap water. Its performance was validated by using reference Au nanoparticles (AuNPs) and Ag-shelled AuNPs. The hyphenated system can determine the actual size and metal composition of both NPs with additional heating after ATM, while stand-alone spICP-MS misidentified the Ag-shelled AuNPs as smaller individual AgNPs and AuNPs. Dissolved metal ions could introduce artifact NPs after heating but could be eliminated by centrifugation. The hyphenated system was applied to characterize Fe-containing and Pb-containing NPs resulting from the corrosion of plumbing materials in tap water. The mode sizes of Fe-containing and Pb-containing NPs were determined to be 110 and 100 nm and the particle number concentrations were determined to be 4.99 × 107 and 1.40 × 106 #/mL, respectively. Cautions should be paid to potential changes in particle size induced by heating for metallic NPs with a low melting point or a high organic content.

Reviewing performance of NSF/ANSI 53 certified water filters for lead removal

Properly certified NSF/ANSI 53 water filters are distributed as a temporary measure to protect residents from risk of exposure to elevated lead (Pb) levels resulting from water system changes and various activities. Water consumers and other stakeholders have raised questions on the performance of these filters in field settings, particularly in cases where water Pb levels exceeded the NSF/ANSI 53 challenge water level of 150 µg/L and when Pb phosphate nanoparticles (≤ 200 nm) were present in drinking water. This literature review summarizes findings from 23 studies that evaluated the ability of NSF/ANSI 53 post-2007 certified filters to reduce soluble and/or particulate Pb from water. The studies in total examined 1,486 faucet-mounted, 25 under-the-sink, and 167 pitcher filters, with 1,528 filters used in field studies and 150 filters in laboratory studies. This review found that filter performance varied with different filter type, test water source, and initial unfiltered total Pb concentration. 99% (1,512/1,528) of the filters used in field studies removed Pb to at or below the certification benchmark of pre-2019, 10 µg/L or post-2019, 5 µg/L. In contrast, 61% (91/150) of the filters used in laboratory studies reduced Pb to the benchmark. Laboratory filters were often tested under conditions beyond what they were certified to handle. Pb concentration, particle form and size, improper operation and maintenance of certified water filters were attributed to reported filter failures. This information is intended to help water utilities, regulators, and others make decisions regarding the deployment of water filters to the public when drinking water Pb exposure concerns have been raised.