Public Health 

Assessments & 

Health Consultations

Page last reviewed: October 16, 2009

Page last updated: October 16, 2009

Content source: Agency for Toxic Substances and Disease Registry 

Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, 

Atlanta, GA 30341 

Contact CDC: 800-232-4636 / TTY: 888-232-6348

HEALTH CONSULTATION

WELSH RESERVOIR 

MOUNT PLEASANT, TITUS COUNTY, TEXAS

September 30, 1998

Prepared by:

Texas Department of Health 

Under Cooperative Agreement with the 

Agency for Toxic Substances and Disease Registry

TABLE OF CONTENTS

BACKGROUND AND STATEMENT OF ISSUES

DISCUSSION

ATSDR's CHILD HEALTH INITIATIVE

CONCLUSIONS

RECOMMENDATIONS

REFERENCES

PREPARERS OF REPORT

CERTIFICATION

Next Section

 

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Public Health 

Assessments & 

Health Consultations

HEALTH CONSULTATION

WELSH RESERVOIR 

MOUNT PLEASANT, TITUS COUNTY, TEXAS

BACKGROUND AND STATEMENT OF ISSUES

The Texas Department of Health Seafood Safety Division (SSD) requested that the Health 

Risk Assessment and Toxicology Program reevaluate the current advisory limiting 

consumption of fish taken from Welsh Reservoir, a 1,365 acre cooling reservoir for Welsh 

Power Plant and operated by Southwestern Electric Power Company (SWEPCO). Welsh 

Reservoir is located 11 miles southeast of Mount Pleasant in Titus County, Texas. During the 

late 1970's, several power plant cooling reservoirs in Texas received discharges from ash 

ponds containing elevated selenium levels, resulting in increased selenium concentrations in 

fish. An investigation of a series of fish kills in waterbodies near power plants in the early 

1980's implicated elevated levels of selenium in fish tissue and water. The Texas Parks and 

Wildlife Department (TPWD) reported levels of selenium in Welsh Reservoir fish ranging 

from 2.28 to 4.41 ppm from 1986-1989.

Since the fish kills, the Texas Department of Health (TDH), TPWD, and SWEPCO have 

worked cooperatively to monitor selenium levels in fish tissue. In 1992, TDH issued a fish 

consumption advisory for the reservoir after it was determined that the levels of selenium in 

fish could pose a potential health risk. The advisory recommended that adults consume no 

more than one eight-ounce meal each week and children seven years of age and older 

consume no more than one four-ounce meal each week. Children six and under, pregnant 

women, or women who may soon become pregnant were advised not to consume the fish. 

Additionally, persons consuming fish from the reservoir were advised not to consume 

mineral dietary supplements with selenium exceeding 50 micrograms per day.

In 1998, TDH collected 20 fish (12 largemouth bass, 6 channel catfish, 1 flathead catfish, and 

1 common carp) for a re-evaluation of the present fish consumption advisory. The 

concentration of selenium in the fish ranged from 1.2 to 4.5 ppm with an overall average 

concentration of 2.7 ppm (Table 1). Selenium levels in fish from Welsh Reservoir continue to 

be above reported national averages (0.1 to 1.5 ppm [1]). The average concentration of 

selenium in fish from Welsh Reservoir ranged between 2.2 and 4.4 ppm from 1986 to 1989 

(Figure 1). There is no clear indication of an overall change in selenium concentrations in 

fish tissue over the 12 years of investigation; however, there is a 9 year period (1989-1998) in 

which there are no data to represent an overall increase or decrease in average 

concentrations. The maximum average concentration of 4.4 ppm selenium in fish tissue 

occurred in 1987. 

Table 1. Selenium in Welsh Reservoir Fish

November 1996

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Species # 

collected

Size Selenium Range 

(ppm)

Selenium Average 

(ppm)

February 1998

Largemouth 

Bass

12 18 - 20" 1.87 - 3.88 2.97

Channel Catfish 6 18 - 

23.5"

1.2 - 2.44 1.78

Flathead Catfish 1 28" 2.78 2.78

Common Carp 1 24" 4.5 4.5

All Fish 2.7

DISCUSSION

Selenium

Selenium is a naturally occurring substance that is widely, but unevenly distributed in rocks 

and soils of the earth's crust. It is rarely found in pure form in the environment. When rocks 

decompose into soils, selenium often combines with sodium and oxygen to form sodium 

selenate, or with water to form sodium selenite, both of which are water soluble. Plants easily 

take up inorganic selenium compounds from water and change them to organic selenium 

compounds such as selenomethionine. The major man-made source of selenium in the 

environment is coal burning, especially the fly ash that results from burning coal. Persons 

living near industrial sites may be exposed through ingesting the soil or water, breathing the 

dust, eating plants that may have taken up selenium from soil, or ingesting fish that may 

have taken up selenium from high concentrations in water [2]. The estimated 

bioaccumulation factor for selenium in fish ranges from 485 to 1,746, depending on the 

species [3]. In general the more soluble and mobile forms of selenium (selenite and selenate) 

dominate under aerobic (high oxygen concentrations) and alkaline (high pH) conditions [2]. 

Humans and animals are both capable of absorbing and utilizing both organic or inorganic 

forms of selenium from food or water sources. Most of the selenium that enters the body is 

excreted in the urine within 24 hours. Selenium can build up in the body if exposure is high 

and occurs over a long period of time. Body burdens of selenium primarily occur in the liver, 

kidneys, hair, and nails. Selenium is an essential dietary element for both human and 

animals in either the inorganic or organic form. Selenium has antioxidant effects which help 

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prevent damage to tissues caused by oxygen. A selenium deficient diet can result in Keshan 

disease, the signs and symptoms of which may include muscle pain, cardiomyopathy, 

enlargement of the heart, increased red blood cell fragility, and pancreatic degeneration. 

The human recommended daily allowance (RDA) of selenium for maintenance of good 

health is 55 micrograms per day (ug/day) for women and 70 micrograms per day for men. 

Estimates of the average intake of selenium from food for the U.S. population range from 71 

to 152 micrograms of selenium per person per day [2]. Welsh et al. reported that about three 

percent of Maryland residents consumed diets which contained over 200 Âμg of selenium 

per day [4]. The Food and Nutrition Board of the National Research Council has estimated 

the safe and adequate daily dietary intake of selenium in adults to be 50 to 200 Âμg [5]. 

However, when eaten in amounts that are not much higher than required for good nutrition, 

selenium becomes harmful to humans and animals [2] (Figure 2). Signs and symptoms of 

sub-acute and chronic toxicity in humans include brittleness and loss of hair and nails; 

blisters, eruptions and skin mottling; pitting and excessive decay of the teeth; a garlic or sour

-milk breath odor; periodic episodes of nausea and vomiting; and increasing fatigue. 

No human populations in the U.S. have been reported to have chronic selenium toxicity, 

including populations in the western part of the country with naturally high levels of 

selenium in the soil and water. In a study of 142 subjects living in a seleniferous area of 

South Dakota and Wyoming, there was no evidence of toxicity from selenium in subjects 

whose intake was as high as 724 ug per day [6]. There have been a limited number of case 

reports of individuals who developed minimal signs of selenium toxicity following chronic 

dietary intakes of 850-900 ug per day. In areas of China with selenium intakes of 3,200 to 

6,690 ug per day, clinically apparent selenium toxicity was observed, while persons with 

daily intakes in the range of 42-750 ug per day did not produce any signs of toxicity or other 

adverse health effects [7].

The Agency for Toxic Substances and Disease Registry (ATSDR) recently has established a 

chronic oral Minimum Risk Level (MRL) for selenium of 5 Âμg/kg/day [1]. For a 70 kg adult 

this is equivalent to an intake of 350 Âμg/day. The MRL is an estimate of the daily human 

exposure to a hazardous substance that is likely to be without appreciable risk of noncancer 

health effects over a specified duration of exposure. The MRL was derived from a study 

involving a Chinese population with high selenium intake. Blood selenium concentrations 

and degree of selenosis were determined for 349 adults. The endpoint used to derive the 

MRL was nail disease, specifically brittleness of nails. By regression analysis the 

corresponding selenium dietary intakes were determined. A "no observable adverse effects 

level" (NOAEL) of 15 ug/kg/day, was determined. The NOAEL is the highest dose at which 

no statistically or biologically significant adverse effects were observed. For a 70 kg adult this 

dose is equivalent to a selenium intake of 1,050 Âμg/day. To establish the MRL, ATSDR 

divided the NOAEL by a factor of three to account for human variability. It is important to 

note that the MRL based on the Chinese study may be conservative because only dietary 

exposure was considered and it has been suggested that inhalation exposure to selenium in 

smoke was significant. The population studied cooked their meals on open fires of coal 

containing high concentrations of selenium.

Carcinogenicity

The EPA and the National Toxicology Program have determined that selenium is not 

classifiable as a carcinogen and it is rated as a Group D chemical. In fact, studies of cancer in 

humans suggest that lower than normal selenium levels in the diet may increase the risk of 

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cancer. This may be due to the fact that selenium is used in the body in enzymes that protect 

against oxidative damage to tissues which may be responsible for cancer promotion. One 

specific form of selenium, called selenium sulfide, is a probable human carcinogen. Selenium 

sulfide is not found in foods, and is a very different chemical from the organic and inorganic 

selenium commonly found in the environment. Because it is not absorbed through the skin, 

its primary use in the anti-dandruff shampoo Selsun Blue, is considered safe [2].

Toxicological Evaluation

In 1992, when TDH estimated the risks associated with eating selenium contaminated fish, 

an MRL for this contaminant was not available. Using available information, TDH estimated 

400 Âμg/day (5.71 Âμg/kg/day assuming a 70 kg adult) to be a safe and acceptable dietary 

selenium intake. This estimated safe daily intake is remarkably similar to the MRL (5 

Âμg/kg/day) established by ATSDR and provided approximately a 2.6-fold safety factor 

below the current NOAEL of 1,050 ug/day, or the lowest level reasonably expected to result 

in signs or symptoms of toxicity. In performing the risk assessment, TDH determined the 

acceptable daily intake of selenium from fish by subtracting an assumed daily intake of 

selenium from other sources (200 Âμg/day [2.86 Âμg/kg/day assuming a 70 kg adult]) from 

the estimated safe and acceptable daily intake. Thus, for a 70 kg adult, TDH estimated that 

200 Âμg (2.86 Âμg/kg/day) was an acceptable daily intake of selenium from fish.

To evaluate the current risks associated with eating fish from Welsh Reservoir, we used the 

same paradigm used in the previous risk assessment except that we used the MRL 

established by ATSDR. Assuming a background daily intake of selenium from other sources 

of 200 Âμg we estimate that approximately 150 Âμg/day (2.14 Âμg/kg/day assuming a 70 kg 

adult) is an acceptable daily intake of selenium from fish. 

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To determine the actual number of meals that could be consumed without exceeding the 

MRL, we used two values for the concentration term; the arithmetic average and the 95th

percent upper confidence interval (95% UCL) of the arithmetic average. The 95% UCL is 

defined as a value that when calculated repeatedly for randomly drawn subsets of site 

specific data, equals or exceeds the true average 95 percent of the time. The arithmetic 

average should be most representative of the concentration that would be contacted over 

time; however, the 95% UCL of the average provides a conservative estimate of the average 

concentration and is useful to account for sampling variations and suspected seasonal 

variations in fish tissue concentrations.

We estimated the 95% UCL by defining the distribution of selenium in fish tissue from Welsh 

Reservoir using the 1996-97 data and then randomly drawing 1,000 samples of 20 fish from 

that distribution. Averages were obtained for each of the 1,000 samples and the 950th rank 

ordered average was defined as the 95th percentile. Figure 3 provides a graphical 

representation of the relationship between the sample distribution, the arithmetic average, 

and the 95% UCL of the arithmetic average.

Using these assumptions we estimate that adults (70 kg) could eat approximately one and 

one-half to two (eight ounce) meals per week and children (body weight 10-30 kg) could 

consume approximately one-half to one and one-half (four ounce) meals per week of Welsh 

Reservoir fish before exceeding the MRL (Table 2). Individuals would have to consume 

approximately three times these amounts before exceeding the lowest level reasonably 

expected to result in signs or symptoms of toxicity. 

Table 2. Recommended Limitations on Long-Term Fish Consumption by body 

weight

Body 

Weight

Estimates Based on Average and Upper 95% UCL Selenium Levels for 

the 20 fish samples collected

(kg) (lb)

(a) 

Baseline 

exposure 

(b) 

Minimum 

Risk Level 

 

Acceptable 

Daily Intake 

Quantity of fish that can 

be consumed without 

exceeding MRL 

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(Âμg/day)

(BW x 2.86 

ug/kg/day) 

(Âμg/day)

(BW x 5 

ug/kg/day) 

of Selenium 

From Fish

(ug/day)

((b) - (a)) 

Meals per week

Average 

(2.7 ppm)

95% UCL

(3.05 ppm)

Assumes a child body weight and an average meal size of 4 ounces each

10 22 29 50 21 0.5 0.5

20 44 57 100 43 1 0.9

30 66 86 150 64 1.6 1.4

Assumes an adult body weight and an average meal size of 8 ounces each

40 88 114 200 86 1 0.9

50 110 143 250 107 1.3 1.2

60 132 172 300 128 1.6 1.4

70 154 200 350 150 1.9 1.6

80 176 229 400 171 2.1 1.9

90 198 257 450 193 2.4 2.1

100 22 286 500 214 2.6 2.3

ATSDR's CHILD HEALTH INITIATIVE

The TDH has prepared this consult under a Cooperative Agreement with the Agency for 

Toxic Substances and Disease Registry (ATSDR). TDH has included the following 

information in accordance with ATSDR's Child Health Initiative. 

ATSDR's Child Health Initiative recognizes that the unique vulnerabilities of infants and 

children demand special emphasis in communities faced with contamination of their water, 

soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to 

hazardous substances emitted from waste sites and emergency events. They are more likely 

to be exposed because they play outdoors and they often bring food into contaminated areas. 

They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to 

the ground. Children are also smaller, resulting in higher doses of chemical exposure per 

body weight. The developing body systems of children can sustain permanent damage if toxic 

exposures occur during critical growth stages. Most importantly, children depend completely 

on adults for risk identification and management decisions, housing decisions, and access to 

medical care.

Special consideration was given to children's health in this consultation. Children consuming 

one -half to one and one-half (four ounce) meals of Welsh Reservoir fish per week would not 

exceed minimal risk levels for adverse health effects from selenium in fish. 

Next Section Table of Contents

 

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Page last reviewed: October 16, 2009

Page last updated: October 16, 2009

Content source: Agency for Toxic Substances and Disease Registry 

Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, 

Atlanta, GA 30341 

Contact CDC: 800-232-4636 / TTY: 888-232-6348

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Public Health 

Assessments & 

Health Consultations

HEALTH CONSULTATION

WELSH RESERVOIR 

MOUNT PLEASANT, TITUS COUNTY, TEXAS

CONCLUSIONS

There is no clear indication of an overall change in selenium concentrations in fish 

tissue over the 12 years of investigation. The maximum average concentration of 4.4 

ppm selenium occurred in 1987. The average concentration of selenium in Welsh 

Reservoir fish in 1998 is 2.7 ppm.

1.

Depending on body weight (10-30 kg), children could consume approximately one-half 

to one and one-half (four ounce) meals of Welsh Reservoir fish per week before 

exceeding the MRL. Adults (70 kg) consuming approximately one and one-half to two 

(eight ounce) meals of Welsh Reservoir fish per week would not be expected to exceed 

the MRL. Approximately three times these amounts would be required to exceed the 

lowest levels reasonably expected to result in signs and symptoms of toxicity, therefore, 

ingestion of fish at these amounts pose no apparent public health hazard.

2.

RECOMMENDATIONS

The fish consumption advisory issued for Welsh Reservoir in 1992 should be reevaluated based on the current recommended limitations on long-term fish 

consumption.

1.

REFERENCES

IRIS, 1998. Integrated Risk Information System. U.S. Environmental Protection 

Agency, Office of Health and Environmental Assessment, Environmental Criteria and 

Assessment Office. Cincinnati, Ohio.

1.

ATSDR, 1996. Agency for Toxic Substances and Disease Registry. Toxicological Profile 

for Selenium. Atlanta: ATSDR, Aug. 1996.

2.

Lemly, 1985. Toxicology of selenium in a freshwater reservoir: Implications for 

environmental hazard evaluation and safety. Ecotoxicol. Environ. Safety 10:314-338.

3.

Welsh, et al., 1981. Selenium in self-selected diets of Maryland residents. J. Am. Diet 

Assoc. 79-277-85.

4.

FNB, NRC, 1980. Food and Nutrition Board, National Research Council: 

Recommended dietary allowances, 9th ed. Washington, D.C: National Academy of 

Sciences.

5.

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Longnecker, et.al., 1991. Selenium in diet, blood, and toenails in relation to human 

health in a seleniferous area. Am. J. Clin. Nutr. 53:1288-94.

6.

Yang, et.al., 1983. Endemic selenium intoxication of humans in China. Am. J. Clin. 

Nutr. 37:872-81.

7.

PREPARERS OF THE REPORT

Lisa R. Williams, M.S. 

Toxicologist 

Health Risk Assessment and Toxicology Program

John F. Villanacci, Ph.D. 

Director 

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 Welsh Reservoir 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.

Richard Gillig 

Chief, SPS, SSAB, DHAC, ATSDR

Table of Contents

 

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Page last updated: October 16, 2009

Content source: Agency for Toxic Substances and Disease Registry 

Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, 

Atlanta, GA 30341 

Contact CDC: 800-232-4636 / TTY: 888-232-6348

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