Lead as a Contaminant in Water
Pb(OH)2,PbCO3 and Pb2O
Lead has a tendency to be complexed and precipitated by a large number of substances. When released to land, lead binds to soils and does not migrate to ground water. In water, it binds to sediments, and it does not accumulate in fish. This is why it is seldom found in ground waters or natural
waters in more than trace quantities, under 10 g/L. However, source waters that contain lead are an indication that intrusions from industrial, mine, or smelter wastes may have occurred. Typically, the source water contains less lead than the water at the “point-of-use”. Studies indicate that nearly all the lead in users’ tap water does not come from the primary water source or from the municipal treatment plant, but is a result of corrosion of lead containing materials that contact water after leaving the
treatment plant. Lead can enter the home drinking water by leaching from lead service connections,from lead solder used in copper piping, and from brass fixtures.
Sources of Contaminant:
Mostly lead service lines, lead containing solder, and brass fittings
of different types Industrial processes, mines, and smelting (not a direct source into
Potential Health Effects
Children are more at risk than adults
Reduced intelligence, impaired hearing and decreased growth in
Damage to the brain, kidneys, and bone marrow
Damage nervous system and red blood cells
Solid Block and Precoat Adsorption Filters (properly designed
submicron filtration with adsorption media)
Strong Acid Cation Exchange (Na+
NOTE: Lead can exist in water in a broad array of forms, therefore, more than one type of technology may be
needed for adequate removal. Soluble (or dissolved) lead may be removed by ion exchange, reverse osmosis,
adsorption, or distillation. Insoluble (or particulate) lead may be removed by fine filtration and adsorption, reverse
osmosis, or distillation.
HEALTH EFFECTS OF LEAD IN WATER
Lead is a metallic element, it tastes sweet and can enter the human body in different ways. Often times, lead poisoning shows no symptoms. However, signs such as irritability, weight loss, vomiting, constipation, or stomach pain could occur. The human body can be damaged by ingested lead and the most acute cases of lead poisoning can cause death. Damage to the brain, kidneys, and bone marrow can occur with lower exposures. Coma and convulsions can also be associated with lower exposures of lead. Lead can also damage a person’s nervous system and red blood cells. Children are more at risk than adults when it comes to the dangers of ingesting lead. Children will absorb 30-75% of the lead they ingest while adults will absorb only 11%. Individuals with the greatest risk, even with shortterm exposure, are young children and pregnant women. Estimates are, on average, lead in drinking water contributes between 10 and 20 percent of total lead exposure in young children. Reduced intelligence, impaired hearing and decreased growth, are associated with blood levels as low as 10 micrograms of lead per deciliter of blood (g/dL). A 10 g/dL increase in blood levels correlates to a loss of 2 IQ points. Individuals will adsorb more lead if they have poor nutrition than those that have
TREATMENT METHODS FOR LEAD IN WATER
Lead is amphoteric, which means it is capable of functioning either as an acid or as a base. The chemistry of lead is complex since lead may be a soluble ion present in the monovalent or divalent form, a complex ion, a particulate, a hydroxide, carbonate, or oxide, depending upon the pH, alkalinity and other constituents present in the water.
With this broad array of lead forms in water supplies, it is obvious that more than one type of technology may be needed for adequate removal of lead. Soluble lead levels, for example, may be reduced by ion exchange, reverse osmosis, adsorption, or distillation.
Particulate lead may be removed by fine filtration and adsorption. Sodium cycle , strong-acid ion exchange water softening is a well-established technology for removing ionic forms of lead, but the process has its limitations. Typically, ion exchange softeners must be operated at no more than 2.0 to 3.0 gpm flow rate per cubic foot of ion exchange resin for best results. Removal of lead by reverse osmosis is effective because the membrane removes not only the soluble lead impurities by 90 to 95%
typically, but also acts as a barrier to the particulate lead. Forty to sixty percent of the lead found in municipal supplies is present typically in the particulate or insoluble form. Although data is sparse, properly designed and operated distillation units are capable of reducing both suspended and dissolved lead levels. Data verifies that solid block and precoat adsorption filters using a mixture of activated carbon and a lead adsorbent can remove insoluble lead by particulate filtration and adsorption, and soluble lead by
adsorption. Contact time, type and size of activated carbon and the lead adsorbent material, flow rate per unit area, and the design of submicron filter void sizes to ensure effective filtration of precipitated and insoluble lead species are critical to the success of this treatment technology.
POU/POE products are considered to be the preferred method for lead removal, since most lead in drinking water is the result of corrosion in the water distribution and home plumbing system.
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