Thursday, July 3, 2008

Heavy Metals at Home: Part 1: Lead Contamination

Heavy metals are naturally-occurring substances that have been known to cause health-related problems. When absorbed, it can accumulate in the body, displacing minerals that the body would need to continue biological functions. Heavy metals like lead displaces calcium which is important in building strong bones and teeth. Heavy metals can accumulate in vital organs and glands such as the heart, brain, kidneys, liver and bone; increasing one's risk of developing cancer.

There are six elements in the family of heavy metals that are federally-regulated: Lead (Pb), Mercury (Hg), Arsenic (As), Cadmium (Cd), Chromium (Cr), and Antimony (Si). Each article within this series describes a heavy metal, its' sources of contamination and acute and chronic effects on humans. The ways to prevent contamination are also indicated. Scientific terminologies are used to identify substances with heavy metals so that one can search for these terms within the ingredients list of cosmetics, packaged foods and household cleaners.

Lead (Pb) and the compounds resulting from its' combination with other chemicals are regulated or banned at certain quantities due to the effects of acute or chronic exposure. Symptoms of acute poisoning are: loss of appetite, nausea, vomiting, stomach cramps, constipation, difficulty in sleeping, fatigue, moodiness, headache, joint or muscular aches, anemia and decreased sexual drive. Chronic or long-term exposure causes severe damage to the blood-forming nervous, urinary and reproductive systems.

Lead poisoning in children must be prevented as accumulated lead disrupts a child's mental development, leading to lower intelligence later in adulthood.

Lead has been suspected to cause cancers in the lungs, stomach and bladder of rats though the same effects on humans have been non-conclusive. Routes of exposure are oral or respiratory. Babies have been known to absorb lead via the placenta or through lactation. Lead absorption is greater in children than in adults. Once absorbed, it is distributed to blood plasma, the nervous system and soft tissues in organs. It is subsequently redistributed and acumulates in bones and teeth. Approximately 70-90% of the lead that accumulates in humans are found in bones and teeth. Lead can cause genetic damage at it inhibits DNA synthesis and repair, when it interacts with DNA-binding and tumor-suppressing proteins.

Lead (Pb) is a chemical that is refined from mined ore. In its pure form, it is odorless, soft, highly maleable, conductive and yet insoluble in water. When combined with other elements to form lead compounds, it can be relatively soluble in water. Such compounds that are soluble in water are lead acetate, lead acetate trihydrate, lead chloride, lead nitrate and lead subacetate. It's the solubility of these compounds that make it easy to contaminate solids, water and air. Such compounds can also be soluble in alcohol and in nitric or hydrochloric acid.

Most lead is used in batteries for motor vehicles. Lead metals are in ammunition, cable coverings, piping, brass and bronze. Lead acetate is in water repellents that are applied to prevent mildew or mold formation. It is also used as a mordant for cotton dyes. Lead acetate trihydrate can be in varnishes and chrome pigments while lead chloride is a flame retardant. Lead nitrate is a heat stabilizer in nylon and used as a coating on paper for photo thermography.

Lead compounds that are insoluble in water such as lead phosphate and lead stearate are used as stabilizers in the plastic industry. Ceramics can contain lead oxide. Pigments in paints, rubber and plastics can contain lead chromate; a hexavalent chromium known to be carcinogenic. Lead tetraoxide are in plastics, ointments, glazes and varnishes.

Lead can be found in solids (food), air (cigarette smoke), and water (alcoholic beverages). Lead solder used in canned foods were eliminated in 1979, resulting in a marked decrease in lead-contaminated foods. Lead-free gasoline for motor vehicles was also banned in the 70s and therefore airborne lead has been greatly diminished. A 2004 study of the Agency for Toxic Substances and Disease Registry (ATSDR) revealed that drinking water in the US contains less than 5 micrograms per liter of lead. But, the most common source of exposure is by direct ingestion of paint chips and lead-laden dust that are present in old homes. Lead in paints was not restricted until 1978. Lead in plumbing of homes built in the 1930s can also be a source of contamination. Young children are therefore at high risk for lead contamination due to high hand to mouth activity particularly from the infant to toddler years.

The United States government and its related agencies have enacted and implemented regulations to control exposure to lead. These are:

  1. Painted furniture cannot contain lead that is greater than 0.6% of the product's total weight of solid or dried paint film. A similar regulation applies to paints and any other surface coating.
  2. Candles cannot contain more than 0.6% of lead by weight in the metal core and candle wicks.
  3. Toys and other items for children that are painted cannot contain more than 0.06% of total weight of solid or dried paint.
  4. The Toxic Substances Control Act and the Department of Housing and Urban Development (HUD) requires sellers of homes to disclose their knowledge of lead in their homes as there are allowable limits set for floors, interiors window sills, and soil in play areas which is separate from the maximum limit for bare soil in the yard.
  5. The Lead-Based Poisoning Prevention Regulation stipulates that paint used in home renovations not contain more than 1.0 mg/sq. cm of lead or 0.5% by weight.
  6. The Food and Drug Administration requires that the amount of lead that leaches off ceramic tableware (cups, mugs, holloware, flatware) not exceed values that range from 0.5-3.0 micrograms/milliliter of leachable lead.
  7. Lead in food ingredients should not exceed 0.1 to 10 parts per million of lead.
  8. Lead acetate in hair coloring and makeup cannot exceed 0.6% weight to volume of lead. Such cosmetics also need to be labelled such that it warns consumers that the product contains lead.
  9. Lead in coloring additives can be present in 5-70 parts per million.
  10. The maximum permissible level of lead in bottled water is 0.005 mg/liter.
  11. Certain drugs can contain lead from 10-20 ppm.

For more information on lead in paint, dust and soil, and the prevention of contamination; one can contact the National Lead Information Center Hotline at 1-800-424-LEAD or through the EPA's website http://www.epa.gov/.

Lead contamination can be minimized by:

  1. Washing hands to eliminate accumulated lead dust. Stained glass hobbyists are subjected to lead than most.
  2. Flush cold pipes that have been left unused for 6 hours by allowing water to run for 5 seconds to 2 minutes. Lead dissolves easier in warm water than in cold.
  3. If you own or are planning to live in a home built before 1978, check paints for lead. Old paint dusts off in time and can be ingested or inhaled. Homes built prior to 1930 can have lead in pipes so ask when pipes were last replaced.
  4. Inexpensive jewelry and those containing rhinestones or crystal can contain lead. Wear karat gold or buy jewelry from reputable retailers who are likely to test for lead prior to selling their intended products to the general public.
  5. Wash vegetables and produce before consuming. Old orchards may have been sprayed with pesticides containing lead arsenate. These can be absorbed by plants or dust from the soil can land on produce.
  6. Check the water quality from your source of drinking water or irrigation. Lead compounds are soluble in water or acidic water sources.
  7. Avoid living close to mining areas, landfills and other hazardous waste sites as lead can enter the water stream or its dust can contaminate the air.