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HEALTH CONSULTATION - EXPOSURE INVESTIGATION

MANY DIVERSIFIED INTEREST, INCORPORATED
(a/k/a MANY DIVERSIFIED INTERESTS, INCORPORATED)
HOUSTON, HARRIS, COUNTY, TEXAS


BACKGROUND AND STATEMENT OF ISSUES

The Texas Natural Resource Conservation Commission (TNRCC) requested that the Texas Department of Health (TDH) evaluate the potential health risks asociated with exposure to lead contaminated soil in a residential neighborhood adjacent to an inactive former steel casting facility in Houston, Harris County, Texas. The facility, currently referred to as (MDI)/TESCO, operated as a steel casting facility from 1926 until 1992 under the company names Texas Electric Steel Casting Company (TESCO) and San Jacinto Foundry (SJF). During the mid 1980s, a part of the site was leased to Can-Am Resources Group to operate a spent catalyst recycling operation. By 1988, the spent catalyst recycling operations ceased.

The facility was abandoned in 1992 when San Jacinto Foundry, a subsidiary of Many Diversified Interests (MDI), filed for bankruptcy. From about March 1995 through the middle of January 1996, salvage operations were conducted at the site as ordered by the bankruptcy court. These operations included the dismantling of steel buildings and the scraping, transporting, and sale of all surface assets of value.

In January 1996, the TNRCC tested soil at Bruce Elementary School, at some residential locations, and at other areas near the MDI site. Soil at some residential locations and at other areas near the site contained metals at concentrations warranting additional study. The TNRCC requested assistance from the U.S. Environmental Protection Agency (EPA) to conduct additional soil sampling in the neighborhood next to the facility. From February through July 1996, the EPA collected samples from approximately 100 residential properties near the site.

An exact description of the soil sampling protocol was not available for review; however, soil samples were described as composite samples from "front yard, back yard, entire yard, garden," and "side of yard." Not all descriptions applied to each residence; for some residences only "entire yard" was listed, for others only "front, back, or side" yard were listed. For each residence we used the best estimate of the average soil lead concentration to represent the exposure point concentration for that residence. Exposure point concentrations for the residential yards were lognormally distributed with a geometric mean of 374 milligrams of lead per kilogram (mg/kg) of soil and an arithmetic average of 475 mg/kg (Figure 1). Soil lead levels ranged from 59 to 3,180 mg/kg.

In addition to the soil lead data, we were able to obtain blood lead data on 36 children (ages ranging from 13 to 137 months (11 years) who live(d) in the neighborhood. The blood lead data were collected over several years (1993 to 1996) by the City of Houston Health and Human Services Department. For children aged 13 to 137 months, blood lead levels ranged from non-detect to 25 microgram per deciliter (µg/dL) and appeared to be lognormally distributed with a geometric mean of 7.5 µg/dL (Figure 2). The arithmetic average of the blood lead levels was 9.0 µg/dL.


Figure 1: Frequency Distribution Soil Lead levels Residential Yeards


Figure 2: Relative Frequency Distribution Blood Lead Levels


DISCUSSION OF CHILD HEALTH ISSUES

Although lead is naturally present in most soils and is widespread in the human environment, the soil lead levels in this neighborhood are likely the result of human activities. The average soil lead level of 475 mg/kg is significantly higher than the natural levels derived from crustal rock (typically <10 to 30 mg/kg). In urban environments, soil lead can be the result of past automobile emissions, the use of lead-based paint, and contamination from industrial processes that release lead into the environment. Based on available information we could not determine with any degree of certainty the souce of the lead in this neighborhood. It is probable that several of these factors may have contributed.

In spite of the fact that a threshold soil lead level for adverse health effects has not been established, risks associated with lead in soil have been estimated using observed relationships between soil lead levels and blood lead levels in children. Based on observations of neurologic and cognitive dysfunction in children with blood lead levels between 10 and 15 µg/dL, the Centers for Disease Control and Prevention (CDC) has determined that a blood lead level greater than or equal to 10 µg/dL in children indicates excessive lead absorption and constitutes the grounds for intervention [1]. Regression models for the correlation between blood lead levels and soil lead levels predict that soil lead concentrations of approximately 500 mg/kg could result in excess levels of lead in blood [2]. Other models, such as EPA's Integrated Exposure Uptake Biokinetic (IEUBK) model, which predicts blood lead levels based on intake from multiple sources, suggest that the risk of elevated blood lead levels in young children could be of concern at soil lead levels above 400 to 500 mg/kg. Based upon the observed distribution of lead in the soil in this neighborhood, we estimate that approximately 46% of the residences could have soil lead levels greater than 400 mg/kg; approximately 34 percent could have soil lead levels greater than 500 mg/kg. Eight percent of the homes could have soil lead levels greater than 1,000 mg/kg.

Infants and children are exposed to lead mainly through diet and ingestion of non-food materials because of their normal early hand-to-mouth behavior. The degree to which hand-to-mouth behavior contributes to blood lead levels depends on the levels of lead in house dust, soil, and paint. In the United States, leaded paint continues to cause most of the severe lead poisoning in young children because it is the most widespread source and has the highest concentration of lead per unit of weight [1]. That young children are more likely to be exposed to lead in the environment is supported by the limited blood lead data available from this neighborhood.

Preschool-age children and fetuses are usually the most vulnerable to the effects of lead. The developing nervous system of fetuses and neonates are more susceptible to the neurotoxic effects of lead; in addition, the efficiency of lead absorption from the gastrointestinal tract is greater in children than in adults. Infants often are born with some lead in their bodies due to their mother's past exposure to lead. Exposure to lead during pregnancy has been correlated with premature births, low birth-weight infants, and spontaneous abortions. While the impact of maternal and cord blood lead levels below 10 µg/dL have not been well defined, reduced gestational age and reduced birth weight have been associated with blood lead levels of 10 to 15 µg/dL [1]. In addition, lead has been found to lower intelligence quotient (I.Q.) scores, slow growth, and cause hearing problems in children. These adverse effects can persist and lead to decreased performance in school.

Twenty-two (22) percent of the children (all ages) tested in this neighborhood had blood lead levels greater than or equal to 10 µg/dL; however, this includes 18 childen over six years of age. Preschool-age children are usually one of the most sensitive segments of the population with respect to exposure to lead in soil. This is mainly because young children are more likely to play in dirt and to place their hands and other objects in their mouths, increasing the opportunity for soil ingestion. Thirty-nine (39) percent of the children less than 72 months of age (n=18) had blood lead levels greater than or equal to 10 µg/dL (Figure 3). In Texas, we generally find that less than nine (9) percent of the children tested have blood lead levels greater than 10 µg/dL. The average blood lead level for children less than 72 months of age was 11 µg/dL. For children older than 72 months, the average blood lead level was 7 µg/dL and only one child 78 months old had a blood lead level over 9 µg/dL (Figure 3). The overall half-life of lead in blood is estimated to be 36 days ± 5 days [2].

The most serious effect of acute high dose lead exposure is encephalopathy, characterized initially by headache and drowsiness, and in more severe cases by coma, convulsions, and death. Virtually all children who recover from acute lead encephalopathy exhibit residual reduction in intelligence and behavioral dysfunction. Acute encephalopathy is usually associated with high blood lead levels (over 150 µg/dL). Another effect of acute high dose lead exposure is the Fanconi syndrome, an acute injury to the renal tubules, characterized by spillage of glucose, protein, amino acids, and phosphates into urine. We would not expect the soil lead levels in this neighborhood to result in acute high dose lead exposure.

Chronic exposure to low levels of lead has been shown to cause subtle effects on the central nervous system and the hematologic system. Central nervous system effects are manifested as deficits in intelligence, behavior, and school performance [1,3]. Recent information indicates that children with blood lead levels as low as 10 µg/dL can develop neurological and cognitive deficits [1,3]. Anemia is the most serious effect of lead on the hematologic system. Lead-induced anemia occurs primarily by the lead-induced inhibition of several enzymes involved in the production of hemoglobin. The inhibition of some of these enzymes may occur at blood lead levels below 10 µg/dL; however, lead-induced anemia would not be expected to occur at these low blood lead levels. Based on the information reviewed, the soil lead levels in this neighborhood could result in blood lead levels equivalent to those that have been associated with impaired cognitive development. Although the soil lead levels in this neighborhood couldresult in exposures of sufficient magnitude to inhibit enzymes involved in the production of hemoglobin, it is not likely that these exposures would result in anemia.

We were able to match residential soil lead data to 10 children ( seven years of age (84 months) for whom we also had blood lead data. Using EPA's Integrated Exposure Uptake Biokinetic (IEUBK) model, we predicted blood lead levels for each of these children using individual residential exposure point concentrations and ages (at time of blood draw). We compared the model predictions to the measured blood lead levels. Each child's blood lead level was compared to the age/soil lead specific blood lead distribution predicted by the model. Except for the soil lead concentration, model default parameters were used. Only one child's measured blood lead level fell outside of the 5th and 95th percentile limits predicted by the model (Figure 4).


Figure 3: Blood Lead Level vs. Age


Figure 4: Individual Blood Lead Levels Plotted Against Individual Age/Soil Lead Specific IEUBK Predictions With 95% Confidence Limits


CONCLUSIONS

The soil lead levels in some of the residential yards pose a public health hazard to children, particularly to children less than 72 months of age. The average soil lead level of 475 mg/kg is significantly higher than the natural levels derived from crustal rock (typically <10 to 30 mg/kg). Thirty-nine percent of the children under six years of age had elevated blood lead levels compared to 6% of the children over six years of age. We would not expect the soil lead levels in this neighborhood to result in acute high dose lead exposure. Based on the information reviewed, the soil lead levels in this neighborhood could result in blood lead levels equivalent to those that have been associated with impaired cognitive development. Although the soil lead levels in this neighborhood could result in exposures of sufficient magnitude to inhibit enzymes involved in the production of hemoglobin, it is not likely that these exposures would result in anemia.

We would not expect blood lead levels of adults in this neighborhood to be elevated. In general, adults ingest much less soil than children and they absorb much less of the lead that they do ingest.


RECOMMENDATIONS

Actions Planned

  1. The TNRCC and the TDH will notify residents of the soil sampling results and offer suggestions to minimize exposure. Residents will be provided with their individual test results along with an interpretation of those results. TNRCC and TDH will provide residents with educational materials pertaining to lead exposure. An all day availability session was scheduled for May 12, 1998; TNRCC and TDH will be available to answer any question that residents may have.

  2. The TNRCC is planning to conduct a removal of some residential yard soils in the residential area near the MDI/TESCO site.

Actions Suggested

  1. Blood lead testing for children living in homes identified with elevated soil lead levels is recommended. Particular emphasis should be placed on children less than seven years of age.

  2. Blood lead testing also should be offered to other children (emphasis on children less than seven years of age) living in neighborhood homes that have not been sampled. Soil from these homes should be sampled and tested for lead content.

REFERENCES

  1. CDC, 1991. Centers for Disease Control. Preventing Lead Poisoning in Young Children, A Statement by the CDC. U.S. Department of Health and Human Services, Public Health Service, October 1991.

  2. Schilling R, Bain RP, 1989. Prediction of children's blood lead levels on the basis of household specific lead levels. American Journal of Epidemiology; 128(1):197-205.

  3. ATSDR, 1998. Agency for Toxic Substances and Disease Registry. U.S. Department of Health and Human Services, Public Health Service, February 1998.

PREPARERS OF THE REPORT

John F. Villanacci, Ph.D.
Co-Director
Environmental Epidemiology and Toxicology Division

Susan L. Prosperie
Environmental Specialist
Health Risk Assessment and Toxicology Program

ATSDR REGIONAL REPRESENTATIVE

George Pettigrew, P.E.
Senior Regional Representative
ATSDR - Region 6

ATSDR TECHNICAL PROJECT OFFICER

William Greim
Environmental Health Scientist
Division of Health Assessment and Consultation
Superfund Site Assessment Branch


CERTIFICATION

The MDI/TESCO, Inc Health Consultation was prepared by the Texas Department of Health under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR). It is in accordance with approved methodology and procedures existing at the time the health consultation was initiated.

William Greim
Technical Project Officer, SPS, SSAB, DHAC

The Division of Health Assessment and Consultation, ATSDR, has reviewed this Health Consultation and concurs with its findings.

Sue E. Ribald
Chief, SPS, SSAB, DHAC, ATSDR



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