Chemistry: analytical and immunological testing – Metal or metal containing – Organometallic compound determined
Reexamination Certificate
1999-06-18
2002-12-03
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Metal or metal containing
Organometallic compound determined
C436S073000
Reexamination Certificate
active
06489170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a method and apparatus for qualitatively determining the presence of lead in lead-based paint and other media while avoiding barium or other interferences by use of sodium rhodizonate and a strong acid.
2. Description of Related Art
For hundreds of years, people have used lead for different purposes. Lead was used by the Romans for soldering pipes, by others in crystal glassware, and currently in paint mixtures, as well as other applications. The hazards of lead poisoning have been known, but only in relatively recent times has the extent of the threat to children moved to the forefront. The ingestion of lead is harmful to people of all ages, but is more damaging to children under six, and unborn fetuses. The developing nervous system is more susceptible to the toxic effects of the lead. Children who have been exposed to lead exhibit behavioral and cognitive impairment at low levels, with higher levels resulting in anemia, brain damage and other irreversible effects. The risk of lead poisoning to children from lead-based paint was identified as early as 1897.
Children are exposed to lead in lead-based paint through normal childhood behaviors, such as sucking and chewing on painted surfaces, and ingesting paint chips from damaged areas. If lead-based paint is removed without appropriate precautions, the airborne particles permeate the area, and can be ingested or inhaled by both children and adults.
It is believed that ninety percent of houses built before 1940 contain lead paint. In houses built before 1950, paints used in housing contained as much as 50% lead by dry weight. After the 1940s, the use of lead-based paint decreased in residential homes.
It is estimated that more than 70% of homes built before 1980 have lead in paint and fixtures. It was commonly used in areas where durability was desired, such as trim, cabinets and outdoor areas.
In 1972 the Consumer Products Safety Commission made the first effort to regulate the lead content in paint. The Commission established a maximum lead content in paint at 0.5% lead w/w in residential paint. This limit was considered to be “safe”. In 1977, lead was even further restricted from use in residential paints due to the risk of lead poisoning in children. Any lead content below 0.06% was considered as “lead-free” paint. Any paint with a lead content greater than 0.06% was still considered to be lead-based paint.
In 1990, the U.S. Department of Housing and Urban Development (“HUD”) published “Lead-Based Paint: Interim Guidelines for the Identification and Abatement of Lead- Based Paint in Public and Indian Housing.” The HUD guidelines described technical protocols, practices and procedures for testing, abatement, and worker protection in cleanup and disposal of lead-based paint. The HUD guidelines also required inspection of public and Indian housing before 1994, and abatement if the amounts exceeded an action level of 0.5% lead w/w, or 1 mg/cm
2
mass/area concentration.
Although there are no federal requirements to abate lead in private housing, in 1992 the Residential Lead-Based Hazard Reduction Act, Title X, was passed, to become effective in 1995. Title X established new requirements for homeowners and Federal agencies, and new actions to improve the safety and effectiveness of lead-based paint identification and remediation activities. This act requires the sellers of homes to disclose the existence of any lead-based paint or hazard in pre-1978 homes, and allow purchasers 10 days to inspect before becoming obligated to purchase the house.
In response to requirements made by Title X, HUD issued new guidelines, entitled “The Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing.” This document provides detailed guidance on identifying lead-based paint and associated hazards in housing, and controlling the hazards safely and efficiently. A significant change made by Title X and the subsequent guidelines was in the working definition of lead-based paint. Lead-based paint hazards now became “any condition that causes exposure to lead from lead-contaminated dust; bare lead-contaminated soil; or lead-based paint that is deteriorated or intact lead-based paint present on surfaces, or impact surfaces that would result in adverse human health effects.” U.S. Department of Housing and Urban Development,
The Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing
. Government Printing Office, 1995, p.1-S. Under this definition, intact lead-based paint was not considered a hazard, but should be monitored and controlled. An exception to monitoring plans was still made for Indian and public housing, where the requirement exists to abate if the housing is modernized.
The requirement of Title X for sellers to disclose the existence of lead-based paint in older homes, based on the HUD guidelines, makes it extremely important to have an inexpensive, yet accurate means of testing the existing paint.
Identifying lead-based paint by HUD guidelines can be accomplished by either portable x-ray fluorescence analyzers (XRF) or by laboratory analysis of paint chips. XRFs are expensive to purchase, have radioactive sources, and operators must be trained and licensed. A laboratory analysis is time-consuming, and may also be very costly. Since lead-based paint hazards have gained attention, less costly methods have been developed to identify qualitatively lead-based paint.
Two tests that have been developed include sodium sulfide, and a one-step sodium rhodizonate test. These tests have been put into use in spite of their limitations, which include false positives, false negatives, excessive time required for color change, and difficulties seeing the appropriate color change indicating a positive result.
The “one-step red” sodium rhodizonate test is actually the first step of a test which has been used in the past for the identification of both barium and lead. Use of the “one-step red” test ignores the previously established limitations of the same procedure. In the past, the results provided by the red color in a positive “one-step red” test indicated the presence of both lead and barium. An additional step was required to differentiate between the two, and for the results to be conclusively interpreted as lead.
Recent years have seen an application of a portion of the sodium rhodizonate test to a new area of interest in lead determination. With the concern regarding the presence of lead in paints used in the past, simple testing methods have become advantageous for use in the field. These tests allow the user to make a qualitative analysis of the lead content in a painted surface. The test results can provide the basis for determining the hazards that may arise from the paint removal, or continued exposure to the painted surface. If a field test is not available, the only alternative is instrumental analysis methods, which require laboratory testing or expensive field instruments. Simple testing kits, using the first step in the sodium rhodizonate test, were patented in the early 1990s. These became commercially available, and were accepted for qualitative lead identification in the field. The results of these tests were often used to decide the hazards of the painted surface and the method for paint removal. If the test indicated that the paint was leadbased, considerable expense could be incurred in the removal. Due to variations in the size and conditions of the building, local labor, the market competition, and the type of control selected, cost estimates are difficult; however, in 1991 HUD estimated that control in more than half of the affected housing units could be accomplished for less than $2500 apiece. This cost does not include the initial testing costs, a risk assessment if needed, or the relocation of the occupants during the hazard control.
The interpretations of the results obtained by the new methods in use, however, are in opposition to the interpretations currently accepted by the forensic science com
Cahoon Colin P.
Carstens Yee & Cahoon, L.L.P.
Cole Monique T.
Warden Jill
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