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The Texas Natural Resource Conservation Commission (TNRCC) requested that the Texas Department of Health (TDH) evaluate the potential health risks associated with drinking water from a private well in Palacios, Texas. The TNRCC Site Discovery and Assessment Program sampled water from the well during a preliminary assessment of the HuMar Chemical Corporation site. Sample results show the water to contain lead at a concentration of 226 micrograms per liter of water (g/L). The water also contained manganese and zinc at concentrations of 3,090 g/L and 7,650 g/L, respectively.


Health Assessment Comparison Values

To assess the potential health risks associated with the contaminants found in the residential well water we compared the contaminant concentrations to health assessment comparison (HAC) values for non-carcinogenic endpoints. HAC values are media specific contaminant concentrations that are used to screen contaminants for further evaluation. Non-cancer comparison values are based on the Agency for Toxic Substances and Disease Registry's (ATSDR's) minimal risk levels (MRLs), the U.S. Environmental Protection Agency's (EPA's) references doses (RfDs), or other non-carcinogenic health-based comparison values. MRLs and RfDs are estimates of a daily human exposure to a contaminant that is unlikely to cause adverse non-cancer health effects over a lifetime. Exceeding a HAC value does not imply that a contaminant represents a public health threat but suggests that the contaminant warrants further consideration. Lead concentrations were compared to EPA's Action Level for this contaminant.

EPA's Action Level for lead in drinking water can be used as a guide when assessing the public health significance of lead in drinking water.


Based upon the information reviewed, lead is the primary contaminant of concern. Preschool-age children and fetuses are usually the most vulnerable segments of the population for exposure to lead. Infants and children are exposed to lead mainly through diet and ingestion of non-food materials associated with normal early hand-to-mouth behavior. Chronic exposure to low lead levels has been shown to cause subtle effects on the central nervous system which can result in deficits in intelligence, behavior, and school performance. Recent information indicates that children with blood lead levels as low as 10 g/dL can develop neurological and cognitive deficits. In addition, lead has been found to lower intelligence quotient (I.Q.) scores, slow growth, and cause hearing problems in children. Available evidence is not sufficient to determine whether lead-associated deficits are irreversible. Lead is especially harmful to unborn children. Exposure to lead during pregnancy has been correlated with premature births, low birth weight infants, and spontaneous abortions [1].

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. Exposure to lead has been associated with hypertension, renal failure, and gout. Lead has not been shown to be carcinogenic in humans; however, high doses of lead have been found to produce kidney tumors in laboratory studies of rats and mice. The extremely high cumulative doses of lead used in animal studies are difficult to extrapolate to low-level exposure in humans, and do not provide a sufficient basis for quantitative risk assessment. Based on animal data, EPA currently classifies lead as a B2 carcinogen (probable human carcinogen) [1].

Although no threshold level for adverse health effects has been established, evidence suggests that adverse effects occur at blood lead levels at least as low as 10 g/dL. The Centers for Disease Control and Prevention (CDC) has determined that a blood lead level greater than or equal to 10 g/dL in children indicates excessive lead absorption and constitutes the grounds for intervention. The 10 g/dL level is based on observations of enzymatic abnormalities in the red blood cells at blood levels below 25 g/dL and observations of neurologic and cognitive dysfunction in children with blood lead levels between 10 and 15 g/dL [2].

It is difficult to determine with any degree of certainty the risks associated with the lead found in water from the residential well. However, a lead concentration of 226 g/L could present a health threat particularly if children use the water. Children absorb a greater proportion of ingested lead and, as mentioned previously are more susceptible to the subtle effects of ingesting lead. Using EPA's Integrated Exposure Uptake Biokinetic (IEUBK) model, the probability is high (approximately 81%) that a child chronically ingesting water containing 226 g-lead per liter of water would have a blood lead level greater than 10 g/dL (Figure 1).

Figure 1

Figure 1 Image



Zinc was found in the water at a concentration of 7,650 g-zinc per liter. Zinc is an essential food element needed by the body in small amounts. Too little zinc in the diet can lead to poor health, reproductive problems, and lowered ability to resist disease. However, too much zinc can be harmful to human health. The Recommended Dietary Allowances (RDAs) for zinc are 15 mg/day for men and 12 mg/day for women. Ingesting high doses of zinc (10-15 times higher than the RDA), even for a short time, may result in stomach cramps, nausea, and vomiting [4].

Ingesting high levels of zinc (150 mg/day or more) for several months has been shown to produce copper deficiency and anemia as a result of the intestinal interaction of zinc and copper. Other adverse health effects of chronic excess zinc ingestion include gastric erosion, damage to the pancreas, and decreased levels of high-density lipoprotein (HDL) cholesterol. The Agency for Toxic Substances and Disease Registry (ATSDR) has adopted a chronic oral Minimal Risk Level (MRL) for zinc of 0.3 mg/kg/day. In general, the chronic oral MRL is an estimate of the daily exposure to a substance that is likely to be without appreciable risk of adverse (noncarcinogenic) effects over a chronic duration of exposure. The oral MRL for zinc is equivalent to EPA's reference dose for zinc and is based on hematological effects observed in women given daily supplements of 50 mg zinc as zinc gluconate for 10 weeks [5]. Specifically, the observed effects included decreased hematocrit, serum ferritin, and erythrocyte superoxide dismutase activity. Accounting for a normal dietary intake of zinc, a lowest observable adverse effects level (LOAEL) of 1 mg/kg/day was derived for the most sensitive individuals. This LOAEL was divided by an uncertainty factor of three to derive the MRL. Based on the concentration of zinc found in this well, a 70kg adult would have to drink over 2 liters of water per day to exceed the chronic oral MRL and over 9 liters of water per day to exceed the LOAEL


Manganese is a naturally occurring substance found in many types of rock and soil. Persons living near a coal or oil-burning factory may be exposed to higher levels of manganese since it is released into air when fossil fuels are burned. Manganese can be found in groundwater as a result of its use in the production of batteries, pesticides, and fertilizers. The average level of manganese in drinking water is approximately 4 ug/L [1]. The level of manganese in water from the residential well near the HuMar Chemical Corporation was 3,090 g/L.

Although the concentration of manganese in the water is greater than the EPA's secondary drinking water standard for this contaminant (50 g/L), this standard was set for aesthetic reasons and is not health based. Manganese is an essential dietary nutrient; the World Health Organization (WHO) has estimated the average dietary intake of manganese to range from approximately 2,000 to 8,800 g/day. The Food and Nutrition Board of the National Research Council has established "estimated safe and adequate daily dietary intake levels" for this nutrient that range from 300 g per day for infants to 5,000 g/day for adults (see Table 1). The WHO had concluded that 8,000 to 9,000 g/day is "perfectly safe" for adults [2]. For most people, food is the primary source of manganese exposure. The Environmental Protection Agency has estimated that the typical human intake of manganese from food is 3,800 g/day [7].

Table 1.

Food and Nutrition Board of the National Research Council's Estimated Safe and Adequate Daily Dietary Intake Levels (ESADDIs) for Manganese
Age Range Estimated Safe and Adequate Daily Dietary Intake Level
Birth to 6 months

1 to 3 years

4 to 6 years

7 to 10 years

Adolescents > 11 years and Adults

300 to 600 g/day

1,000 to 1,500 g/day

1,000 to 2,000 g/day

1,000 to 2,000 g/day

2,000 to 5,000 g/day

Excess exposure to manganese can be harmful to human health. A combination of symptoms resulting in a disease known as manganism has been observed in mining and steel workers after long-term exposure to high levels of manganese dust in the air. These symptoms include weakness, abnormal gait, ataxia, muscular hypotonicity, and a fixed facial expression. Manganism occurs when too much manganese adversely affects the brain. Although some of the symptoms of manganism can be treated, the damage that occurs to the brain is permanent [6].

It is not known whether eating or drinking too much manganese can cause manganism. There is one study indicating a statistically significant difference in neurologic test scores between people from one area with high levels of manganese in well water compared with people from another area with low levels of manganese in well water. The concentration of manganese in the water from the high concentration area ranged from 1,600 to 2,300 g/L; however, because of other limitations this study could not be used to determine a quantitative dose response relationship for the toxicity of manganese in humans [6].

Although no MRLs or RfDs have been established for manganese, ATSDR has used the upper range of the ESADDI (5,000 g/day) to establish an interim guidance value of 0.07 mg/kg/day [((5,000 g/day) /(70 kg)) / 1,000 g/mg]. At this residence adults drinking more than 1.6 liters of water per day would exceed the interim guidance level. Children drinking less than one liter of water per day could exceed the interim guidance level (Table 2).

Table 2.

Estimated Water Ingestion Rates for Different Body Weights Needed to Exceed ATSDR's Interim Guidance for Manganese
Body Weight kg 10 15 25 40 50 60 70 80 90
lb. 22 33 55 88 110 132 154 176 198
Ingestion Rate L/day 0.22 0.34 0.57 0.91 1.1 1.4 1.6 1.8 2.0

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