Recent events confirm that lead is a worrisome toxic. Reports of drinking water contaminated with lead that exceeds the maximum level recommended by the federal government have recently appeared in newspapers in Washington, DC; Boston; Seattle; Norwood, MA; Bushwick, NY; Las Cruces, NM; Lansing, MI; Richmond, VA; Denver; and Maui, HI, and have caused public officials and consumers to be even more anxious about the quality of their drinking water.

Lead in drinking water can cause a variety of adverse health effects when exposed to it at levels above the maximum contaminant level (MCL) of 15 ppb for relatively short periods of time. In babies and children, exposure to lead in drinking water can result in:

• Delays in physical and mental development;
• Slight deficits in attention span;
• Hearing problems;
• Learning disabilities.

Adults who drink water contaminated with lead could develop high blood pressure. A lifetime of exposure to lead at levels above the MCL potentially could cause:

• Stroke
• Kidney disease
• Cancer

Lead is rarely found in source water; however, lead mining and smelting operations may be sources of contamination. The greatest concern is lead entering tap water through the corrosion of plumbing materials.

There are 783 drinking water treatment devices certified by NSF International to reduce lead under NSF/ANSI Standards 53, 58, or 62 (see Table 1).

Consumers concerned about lead contamination have many options available, ranging from pour-through pitchers, faucet-mounted filters and countertop units, to drinking water systems plumbed in to a separate tap (see Table 2).

In the late 1970s, testing revealed that compacted carbon filters, formulated without a lead adsorbent, were effective in reducing lead.

By 1990, compacted carbon block filters – carbon-only formulations – were certified by NSF under Standard 53 for the reduction of lead. The capacity of the carbon-only filters was limited by the carbon’s ability to reduce the concentration of lead cations.

A typical carbon-only filter would have a capacity of about 500 gallons to 900 gallons with a performance indicator.

Filter performance life increased substantially with the introduction of lead adsorbents. Lead adsorptive filtration media have a high capacity for removal of lead and other heavy metals from water, thus boosting the capacity of a typical compacted carbon block filter to 800 to 1,200 gallons.

Larger filters, of course, would perform at even higher capacities.

The capacity of a carbon block filter will increase significantly when a lead adsorptive media is used along with the carbon.

Lead adsorptive media is available in powder or granular form. It can be incorporated onto the surface of activated carbon granules or blended with granular activated carbon for use in producing compacted carbon block filters or extruded carbon blocks.

When blending powdered media with carbon, special care should be taken to assure that there is sufficient particle distribution throughout the mix.

Filters of all shapes and sizes can be produced using carbon formulations containing a lead adsorbent media. Carbon block filters will maintain typical properties of granular activated carbon for the reduction of chlorine, chemicals, disinfection by-products (DBPs), and pesticides, in addition to reducing high concentrations of lead.

The performance of a carbon filter with a lead adsorbent will vary with the pH of the water. Higher pH, in general, tends to make the lead more difficult to remove.

Not all lead adsorbents perform the same. The overall performance of a filter will be determined by the character of activated carbons and lead adsorptive media, as well as the technology used to produce the filter.

Carbon block filters that combine mechanical filtration, electrokinetic adsorption and physical/chemical adsorption provide the most effective contaminant reduction possible. Contaminants with a physical size down to 0.5 micron (mm) are removed by electrokinetic adsorption and/or mechanical filtration.

Compacted carbon block filters have a large surface area for chemical/physical adsorption to take place.

Compression of the filter enhances the kinetics and provides performance that cannot be achieved with granular activated carbon (GAC) filters or even extruded filters. The water contact time is longer and provides for greater adsorption of many different chemicals, pesticides, herbicides and certain heavy metals, such as lead and mercury.

Paula I. Rice is the vice president, administration of Multi-Pure Drinking Water Systems, a Las Vegas-based contract manufacturer of solid carbon block filters. Rice can be reached at (702) 360-8880 or email: administration@multipureco.com