NAVAL AIR STATION PATUXENT RIVER
(a/k/a PATUXENT NAVAL AIR STATION
PATUXENT, ST. MARY'S COUNTY, MARYLAND
PCB’s and the pesticide DDT and its degradation products DDE and DDD are the contaminants of concern in fish harvested from NAS Patuxent River ponds. A fraction of each of these compounds when ingested can pass across the placental barrier from pregnant women to their unborn children and in milk from lactating mothers to breast-fed neonates and infants. This health consultation (HC) establishes whether the amounts of these compounds ingested by pregnant women and lactating mothers represent a public health hazard (1) to these women or (2) to their offspring, either from exposure in utero or as a result of nursing.
This HC first addresses the relative exposure to PCBs represented by ingesting fish from NAS Patuxent River Ponds at the consumption limit compared to other sources of exposure to this class of chemicals. Next, available information from the scientific literature is presented bearing on potential human reproductive and developmental effects from PCB exposures. This same approach is then used to characterize exposures to DDT, DDE, and DDD and the possibility of reproductive and developmental effects.
The average concentration of PCBs found in NAS Patuxent River pond fish sampled in 1990 was 116 micrograms/kilogram (mg/kg). This may be equivalently expressed as 116 parts-per-billion (ppb) (2). The average concentration of PCBs in food fish in the United States, measured for the years 1970 to 1976 by a joint U.S. Food and Drug Administration (FDA)/U.S. Department of Agriculture (USDA) monitoring program, was 892 ppb (3). This 892 ppb concentration was greater than ten times the concentrations found in shellfish and eggs and one hundred times that found in meat and poultry in the United States during that same time period. A woman eating 19 meals per year of fish during this period from any source would be expected to ingest over seven times the amount of PCBs represented by similar consumption of fish from NAS Patuxent River ponds currently. Those who ate fish weekly in the early 1970s would have been ingesting nearly 20 times the quantity of PCBs compared to that resulting from currently permitted consumption of fish from NAS Patuxent River ponds.
The manufacture of PCBs stopped in the United States in October 1977 due to evidence of harmful environmental effects. (4) Concentrations of PCBs in foods, including fish, began to decline thereafter. In 1978, an extensive U.S. Fish and Wildlife monitoring program showed an average of 850 ppb PCBs in fish sampled throughout the United States. (5) Corresponding values for fish sampled in 1981 and 1984 were 530 ppb and 390 ppb, respectively. These data suggest PCB degradation processes that approximate first order kinetics, which provide an estimate of 200 ppb PCBs fish marketed in 1990 at the time that NAS Patuxent River pond fish were found to average 116 ppb PCBs. To provide further perspective, the FDA limit for PCBs in food fish is 2000 ppb. That is, fish with less than 2000 ppb PCBs is considered by the Food and Drug Administration sufficiently low in PCBs to be safe for human consumption.
Several conclusions may be drawn from the above data. Concentrations of PCBs in fish have decreased dramatically since the end of PCB production in the United States. In 20 years, concentrations have fallen by an estimated 75%. This is particularly significant since fish bioaccumulate these chemicals to much higher concentrations than other foodstuffs. Exposures to PCBs now are substantially less than in earlier decades, particularly for persons for whom fish comprise a large percentage of their diet.
The ATSDR chronic-duration (>1 year) Minimum Risk Level (MRL) for PCBs is 0.02 mg/kg/day based on immunological effects in monkeys.(6) The average daily intake of PCBs over the period of a year from eating NAS Patuxent River Pond fish is 0.023 mg/kg/day, almost exactly the same as the MRL. This close comparability of the anticipated dose to the MRL (screening) value prompts the detailed assessment of the potential for PCB exposure to cause reproductive and developmental effects that follows. The United States Environmental Protection Agency (USEPA) Oral Reference Dose (RfDo) is 0.02 mg/kg/day for Aroclor 1254 and 0.07 mg/kg/day for Arochlor 1016. The Aroclors are two different, formerly-marketed, commercial mixtures of PCB isomers.(6)
Studies on Reproductive and Developmental Effects of PCBs
ATSDR has reviewed the scientific literature to locate publications that address the question of risk to sensitive human populations from oral exposure to PCBs. The sensitive populations considered for this report include pregnant women, embryos, fetuses, lactating mothers, and breast-fed neonates and infants. The areas of concern are in the categories of reproductive and developmental effects.
Reproductive Effects - No studies were located describing reproductive effects in humans following oral exposure to PCBs; however, data are available from animal studies. The chemical structures of PCBs have similarities to those of estrogenic hormones. At elevated concentrations they can interact with receptors in the body for reproductive hormones. Female monkeys exposed to 100 mg/kg/day of the PCB mixture Arochlor 1248 in the diet for 7 months or more had increased menstral duration and bleeding.(7) Doses of 200 mg/kg/day Arochlor 1254 in the diet for 38 weeks resulted in erratic and longer menstral cycles, postimplant bleeding, abortions, and inability to conceive following recovery from abortions.(8, 9) In another study by the same author, doses of 80 mg/kg/day Arochlor 1254 for 37 months produced no significant reproductive effects. (10) To put the above doses in perspective, the estimated average dietary intake per day of PCBs for persons in the United States is 0.0005 mg/kg/day.(11) Eating 19 fish meals from NAS Patuxent River pond fish in the course of a year would increase the average dietary intake of PCBs per day to 0.0235 mg/kg/day. This is 50-fold higher than without eating the fish; however, this PCBs daily intake (dose) is more than 3000 times lower than the 80 mg/kg/day dose used in the above-cited study that showed no reproductive effects.
In summary, the average daily intake of PCBs expected from consuming NAS Patuxent River pond fish is several thousand times lower than the threshold at which reproductive effects begin to appear in studies on rhesus monkeys. Eating fish from NAS Patuxent River ponds in compliance with the published consumption limits poses no apparent public health hazard from reproductive effects due to quantities of PCBs ingested.
Developmental Effects - Several studies have been reported regarding developmental effects in humans following oral exposure to PCBs. (12) One of these studies bears most directly on the issues addressed by this HC. (13) The investigation was undertaken in Michigan beginning in 1980, where a population of childbearing women who reported eating fish from Lake Michigan was compared with a control group of childbearing women who denied consuming such fish. (Significant concentrations of PCBs have been reported in Great Lakes fish in a number of publications.) (14)
According to the Michigan Study, reported in a series of papers (15,16,17) children of the study (fish eating) group exhibited small but statistically significant neurobehavioral changes, lower birthweights, and a reduced gestation period compared to controls. The authors maintain that these effects result from exposure to PCBs during the gestation period, but they see no association between observed effects and exposures of nursing neonates and infants to PCBs in breast milk. Unfortunately, there are no data on PCB concentrations in the fish that these women report having eaten over a period of years. One source reports that median levels of PCBs in cooked Lake Michigan fish ranged from 170 to 3000 ppb, (18) which is substantially higher than the average of 116 ppb reported for NAS Patuxent River pond fish.
Two reviews, (19,20) of the Michigan Study publications pointed out flaws in the study design and data analysis. Paneth19 maintains that PCB exposure in the study population was poorly defined; dose-response relationships were not well established; and other factors, such as exposure to heavy metals and the mother’s lifestyle, well being, and genetic makeup, were not considered and could cause the observed effects. There was also criticism of the validity of the neurobehavioral tests used in the investigation, questioning their suitability for large population studies.(20)
In summary, the developmental changes, maintained by the Michigan Study authors to be significantly associated with intake of PCB-contaminated fish by pregnant women, are small and of negligible to marginal clinical significance. The authors claim an association with developmental effects from in utero exposure but not as a result of breast feeding of neonates and infants. Moreover, other scientists reviewing the complex issues in the Michigan study cite flaws that they feel cast strong doubts on the conclusion that PCBs caused the observed effects. It is useful to note also that the concentration of PCBs in fish eaten by the Michigan women is estimated at about ten times higher than that in NAS Patuxent River pond fish. The Michigan women averaged the equivalent of 18 fish meals per year when pregnant, approximating the fish consumption limit of 19 meals/year for NAS Patuxent River pond fish. Based on the weight of evidence, it is unlikely that eating fish from NAS Patuxent River ponds poses any public health hazard from developmental effects due to quantities of PCBs ingested.
DDT, DDE, and DDD:
The sum of concentrations of DDT, DDE, and DDD (referred hereafter as total DDT) found in NAS Patuxent River pond fish sampled in 1990 averaged 182 ppb. (21) One meal of fish (taken as 0.228 kg) from NAS Patuxent River Ponds would result in 41.5 mg of total DDT for that day. This one fish meal would result in a dose of 0.692 mg/kg/day for an adult for that day and for each succeeding day that a fish meal is eaten. This dose slightly exceeds the ATSDR oral Minimal Risk Level (MRL) for acute or extended exposure of 0.5 mg/kg/day DDT. (22) The acute-duration oral MRL is based on effects on perinatal development of the nervous system in neonatal mice leading to behavioral neurotoxicity in the adult animals. A number of safety factors are built into the oral MRL. Moreover, the policy of no more than two of the 19 yearly fish meals in a given month gives an average daily total DDT dose of 0.046 mg/kg/day, one-tenth of the oral MRL. The average daily intake for NAS Patuxent River pond fish over one year would be 19/365 x 0.692 mg/kg/day or 0.0360 mg/kg/day. The average intake of DDT in the United States by the oral route dropped from 0.13 mg/kg/day in 1974 to 0.037 mg/kg/day in 1981.(23) The value for this parameter today is expected to be smaller, based on the slow, but inexorable degradation of DDT in the environment over time. To provide prospective, the World Health Organization/Food and Agricultural Organization (WHO/FAO) acceptable daily intake of DDT is 20 mg/kg/day. (24)
We can draw two conclusions from the above data. (1) The average summed daily intake of DDT each year, including that from NAS Patuxent River pond fish meals and the average daily intake in the United States, is well within the ATSDR oral MRL and (2) A fish consumption policy of no more than 19 meals/year and not to exceed two meals in any given month maintains total DDT doses well below the oral MRL for acute (1 to 14 day), intermediate-term (15 to 364 day), and chronic (365 day and longer) exposures.
Studies on Reproductive and Developmental Effects of Total DDT
As was done for PCBs above, we have reviewed the scientific literature to locate publications that address the question of risk to sensitive populations from oral exposure to DDT. The sensitive populations considered include pregnant women, embryos, fetuses, and breast-fed neonates and infants. We focused on reproductive and developmental effects. As with PCBs, DDT at elevated levels can interact with receptors in the body for reproductive hormones.
Reproductive Effects - Two epidemiological studies were found in the literature that investigated human reproductive effects.(25) One reported no association between DDT maternal blood levels and miscarriage, (26) while the other found no association between maternal blood levels and premature rupture of fetal membranes.(27) The acute-duration oral Minimal Risk Level (MRL) and the intermediate-duration oral MRL are both equal to 0.5 mg/kg/day, about ten times the 0.036 mg/kg/day dose represented by eating NAS Patuxent River pond fish at the consumption limit.(28) The ATSDR Toxicological Profile for the DDTs states for animal experiments that "Reproductive studies of chronic dietary DDT exposure or multigenerational studies have not generally indicated reproductive toxicity". (29) In one multigenerational mouse study no effects were seen at 3,200 mg/kg/day. A 13,000 mg/kg/day dose caused decreased viability and lactation indices. A 32,000 mg/kg/day dose caused frank toxic effects and was suspended after three generations. (30) The dose at which no effects were seen, 3,200 mg/kg/day, is over 10,000 times the 0.036 mg/kg/day quantity from from eating NAS Patuxent River pond fish at the consumption limit.
In summary, no reproductive effects have been attributed to DDT in two human studies, and animal studies show effects only at high and/or toxic doses many thousands of times those to which humans are exposed in the environment. Eating fish from NAS Patuxent River ponds in compliance with the published consumption limits poses no apparent public health hazard from reproductive effects due to quantities of total DDT ingested.
Developmental Effects - No studies were located regarding developmental effects in humans after oral exposure to DDT, DDE, or DDD. No significant relationship between DDT, DDE, and DDD concentrations, either in maternal blood or placental tissues, and developmental effects has been found. (31) A number of animal investigations concerning DDT and developmental effects are included in the Toxicological Profile for DDT. (32) Three of these form the basis for the the acute oral MRL value for DDT (33,34,35) This value (0.5 mg/kg/day) was introduced above.
In summary, doses of total DDT from consumption of fish from NAS Patuxent River ponds (0.036 mg/kg/day) are well below the ATSDR acute oral MRL (0.5 mg/kg/day), which is applicable to developmental effects. The intermediate-duration MRL has this same value. Eating fish from NAS Patuxent River ponds in compliance with the published limits poses no apparent public health hazard from developmental effects due to quantities of total DDT ingested.
PCBs and total DDT compounds are structurally similar and certain effects may be partially additive. Even if contributions to some effects were completely additive, the margins of safety described in the above sections are on the order of 10-times or greater.