Low birth weight and residential proximity to PCB-contaminated waste sites.Previous investigations have shown that women exposed to polychlorinated biphenyls polychlorinated biphenyls, (pol´ēklôr´  nā´tid bīfē´n (PCBs) are at increased risk of giving birth
to an infant with low birth weight (< 2,500 g), and that this
relationship is stronger for male than for female infants. We have
tested the hypothesis that residents in a zip code zip codeSystem of postal-zone codes (zip stands for “zone improvement plan”) introduced in the U.S. in 1963 to improve mail delivery and exploit electronic reading and sorting capabilities. that contains a PCB PCB: see polychlorinated biphenyl. PCB in full polychlorinated biphenyl Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. hazardous waste Hazardous waste Any solid, liquid, or gaseous waste materials that, if improperly managed or disposed of, may pose substantial hazards to human health and the environment. Every industrial country in the world has had problems with managing hazardous wastes. site or abuts a body of water contaminated contaminated, v 1. made radioactive by the addition of small quantities of radioactive material. 2. made contaminated by adding infective or radiographic materials. 3. an infective surface or object. with PCBs are at increased risk of giving birth to a low-birth-weight baby Noun 1. low-birth-weight baby - an infant born weighing less than 5.5 pounds (2500 grams) regardless of gestational age; "a low-birth-weight infant is at risk for developing lack of oxygen during labor" low-birth-weight infant . We used the birth registry of the New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of State Vital Statistics to identify all births between 1994 and 2000 in New York State except for New York City New York City: see New York, city. New York City City (pop., 2000: 8,008,278), southeastern New York, at the mouth of the Hudson River. The largest city in the U.S. . This registry provides information on the infant, mother, and father together with the zip code of the mother's residence. The 865 state Superfund sites, the 86 National Priority List sites, and the six Areas of Concern in New York were characterized regarding whether or not they contain PCBs as a major contaminant contaminant /con·tam·i·nant/ (kon-tam´in-int) something that causes contamination. contaminant something that causes contamination. . We identified 187 zip codes containing or abutting PCB-contaminated sites, and these zip codes were the residences of 24.5% of the 945,077 births. The birth weight in the PCB zip codes was on average 21.6 g less than in other zip codes (p < 0.001). Because there are many other risk factors for low birth weight, we have adjusted for these using a logistic regression In statistics, logistic regression is a regression model for binomially distributed response/dependent variables. It is useful for modeling the probability of an event occurring as a function of other factors. model for these confounders. After adjusting for sex of the infant, mother's age, race, weight, height, education, income, marital status marital status, n the legal standing of a person in regard to his or her marriage state. , and smoking, there was still a statistically significant 6% increased risk of giving birth to a male infant of low birth weight. These observations support the hypothesis that living in a zip code near a PCB-contaminated site poses a risk of exposure and giving birth to an infant of low birth weight. Key words: birth registry, confounders, female, inhalation, male, very low birth weight. ********** Low birth weight is an important predictor of infant morbidity and mortality Morbidity and Mortality can refer to:
neonatal mortality rate death rate, deathrate, fatality rate, mortality rate, mortality - the ratio of deaths in an area to the population of that area; expressed per 1000 per year in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. and Canada is associated with low birth weight. This condition is also related to increased infant and childhood morbidity because low-birth-weight infants are 5-10 times as likely to die in the first year of life (Kramer 1987). Recent studies have shown that low birth weight increases risk of several chronic adult diseases, including cardiovascular diseases Cardiovascular disease Disease that affects the heart and blood vessels. Mentioned in: Lipoproteins Test cardiovascular disease (Barker 1999; Rich-Edwards et al. 1997), hypertension (Law et al. 2001), renal failure renal failure n. Acute or chronic malfunction of the kidneys resulting from any of a number of causes, including infection, trauma, toxins, hemodynamic abnormalities, and autoimmune disease, and often resulting in systemic symptoms, especially edema, (Lackland et al. 2000), and type 2 diabetes type 2 diabetes n. See diabetes mellitus. (Forsen et al. 2000; Rich-Edwards et al. 1999). Conventionally, low-birth-weight infants are defined as those born weighing < 2,500 g. This low weight could be caused by shortened gestation (< 37 weeks) and/or inadequate fetal growth. Infants born weighing < 1,500 g are considered very low-birth-weight infants. Very low birth weight is usually a reflection of a more serious problem with pregnancy and thus has a different etiology (Kramer 1987), although there are some common risk factors. Several factors have been proven to be associated with increased risk of giving birth to low-birth-weight babies: mother's age, race, nutritional status nutritional status, n the assessment of the state of nourishment of a patient or subject. and weight before pregnancy, socioeconomic status socioeconomic status, n the position of an individual on a socio-economic scale that measures such factors as education, income, type of occupation, place of residence, and in some populations, ethnicity and religion. and educational level, and mother's smoking status. Premature birth premature birth Birth less than 37 weeks after conception. Infants born as early as 23–24 weeks may survive but many face lifelong disabilities (e.g., cerebral palsy, blindness, deafness). is by far the most common cause of low birth weight. Birth weight and gestational age ges·ta·tion·al age n. See estimated gestational age. Gestational age The estimated age of a fetus expressed in weeks, calculated from the first day of the last normal menstrual period. are usually positively correlated (Kramer 1987). African-American women are twice as likely as white women to deliver a low-birth-weight infant (Goldenberg et al. 1997; Luke et al. 1993). Lack of education and low-income status are also associated with low birth weight (Bruce and Tchabo 1989; Olsen and Frische 1994; Williams 1998). The effect of maternal age maternal age, n the age of the mother at the period of conception. on risk of having a low-birth-weight baby is U-shaped: Women at the youngest ([less than or equal to] 18 years) and oldest (> 39 years old) ends of the childbearing age spectrum are at greatest risk of having a low-birth-weight infant (Abel et al. 2002; Aldous and Edmonson 1993; Goldenberg et al. 1997; Herceg et al. 1994). Cigarette smoking affects birth weight by causing intrauterine growth retardation Intrauterine Growth Retardation Definition Intrauterine growth retardation (IUGR) occurs when the unborn baby is at or below the 10th weight percentile for his or her age (in weeks). (Kramer 1987). Female infants are more likely to be of low birth weight than are male infants (Herceg et al. 1994; Goldenberg et al. 1997). Other risk factors include poor gestational nutrition (Bruce and Tchado 1989; Haste et al. 1990), primiparity primiparity the state of being a primipara. (Herceg et al. 1994), single motherhood (Holt et al. 1997), and mother's short stature Short stature refers to a height of a human being which is below expected. Shortness is a vague term without a precise definition and with significant relativity to context. (Goldenberg et al. 1997; Herceg et al. 1994). Exposure to environmental contaminants also contributes to the increased risk of having a low-birth-weight baby. Numerous studies that looked at the relationship between exposure to environmental hazards and reproductive outcomes used residence in proximity to hazardous waste landfill sites as a surrogate for exposure. A statistically significant association between the mother's residence near hazardous waste sites and risk of having low-birth-weight births was found in some (Berry and Bove 1997; Elliott et al. 2001; Goldberg et al. 1995; Goldman et al. 1985; Vianna and Polan 1984) but not all studies (Baker et al. 1988; Kharazi et al. 1997; Shaw et al. 1992). Most of these studies did not consider the chemical composition of the waste within the sites. Because most waste sites contain multiple chemical components, it is usually not possible to determine which chemicals are responsible for the observed health effects. A key to understanding which contaminant(s) might cause these effects comes from the observation that low birth weight occurs more commonly among women who consume large amounts of fish contaminated with organochlorine or·gan·o·chlo·rine n. Any of various hydrocarbon pesticides, such as DDT, that contain chlorine. compounds, including polychlorinated biphenyls (PCBs), persistent pesticides, and dioxins/furans (Fein et al. 1984; Rylander et al. 1998, 2000; Vartiainen et al. 1998). Fein et al. (1984) noted that PCB-exposed infants averaged 190 g less in weight and 4.9 days less in gestational age, and Taylor et al. (1984, 1989) also reported an increase of low-birth-weight babies and shortened gestational age among women occupationally exposed to PCBs. Rylander et al. (1995, 1996) and Hertz-Picciotto et al. (2000) found that in PCB-exposed populations, low birth weight is more pronounced in male infants than in female infants. Vartiainen et al. (1998) reported that low birth weight was more pronounced in boys than in girls prenatally exposed to dioxins and furans. We have examined the effect of maternal residence in a zip code that contains or abuts a PCB-contaminated site on the birth weight of the baby. We used birth registry data without personal identifiers from the New York State Vital Statistics (New York State Department of Health 1994-2000) to test the hypothesis that living in a zip code that contains or abuts a PCB-contaminated site is a risk factor for giving birth to a low-/very low-birth-weight infant. Although zip code of residence is a very inexact in·ex·act adj. 1. Not strictly accurate or precise; not exact: an inexact quotation; an inexact description of what had taken place. 2. indicator of exposure, some studies have shown that residential proximity to contaminated sites increases risk of several different diseases (Carpenter et al. 2001; Elliott et al. 2001; Gilbertson and Brophy 2001). Materials and Methods The New York State Department of Environmental Conservation has identified 865 hazardous waste sites in the state, and for each lists the chemicals of major concern and the geographical location, including zip code, census track, and geographic longitude and latitude. Additional information is available for those waste sites listed on the U.S. Environmental Protection Agency Environmental Protection Agency (EPA), independent agency of the U.S. government, with headquarters in Washington, D.C. It was established in 1970 to reduce and control air and water pollution, noise pollution, and radiation and to ensure the safe handling and (2003) National Priority List website. After scanning the list of the chemicals under each of the waste sites for the key words PCBs, PCB, Aroclor, and Pyranol, we have identified 128 zip codes in New York containing PCB-contaminated sites. In this study we excluded New York City, which reduced the PCB-contaminated zip codes to 117. We added all zip codes that directly abut To reach; to touch. To touch at the end; be contiguous; join at a border or boundary; terminate on; end at; border on; reach or touch with an end. The term abutting implies a closer proximity than the term adjacent. bodies of water known to be contaminated with PCBs, including a major portion of the Hudson River Hudson River River, New York, U.S. Originating in the Adirondack Mountains and flowing for about 315 mi (507 km) to New York City, it was named for Henry Hudson, who explored it in 1609. Dutch settlement of the Hudson valley began in 1629. and the six Areas of Concern in New York State (areas along the Great Lakes Great Lakes, group of five freshwater lakes, central North America, creating a natural border between the United States and Canada and forming the largest body of freshwater in the world, with a combined surface area of c.95,000 sq mi (246,050 sq km). that have exceptional levels of contamination), as identified by the International Joint Commission. These are the Niagara River Niagara River River forming the U.S.-Canada boundary between western New York and southern Ontario. Its high flow and steep descent make it one of the best sources of hydroelectric power in North America. , Buffalo River Buffalo River can refer to:
River, Pennsylvania and New York, U.S. It flows north from its headwaters in Pennsylvania, bisecting Rochester, N.Y., to enter Lake Ontario after a course of 158 mi (254 km). , and the St. Lawrence River near Massena (Carpenter et al. 2001). The final number of zip codes identified to contain or abut PCB-contaminated sites was 187. Of these, 78 abut the Hudson River; the others were distributed throughout the state. Data on outcomes and potential confounders /effect modifiers were derived from birth certificates collected and stored in New York State Department of Health Vital Statistics files for the years 1994-2000. To estimate socioeconomic status, we used the estimated mean per capita income Noun 1. per capita income - the total national income divided by the number of people in the nation income - the financial gain (earned or unearned) accruing over a given period of time for 1997 (midpoint mid·point n. 1. Mathematics The point of a line segment or curvilinear arc that divides it into two parts of the same length. 2. A position midway between two extremes. between the beginning and the end of the study) in the zip code of the mother's residence. This information was obtained from the New York State Department of Health, which in turn uses data produced by Claritas Inc. (San Diego San Diego (săn dēā`gō), city (1990 pop. 1,110,549), seat of San Diego co., S Calif., on San Diego Bay; inc. 1850. San Diego includes the unincorporated communities of La Jolla and Spring Valley. Coronado is across the bay. , CA). Inclusion criteria
Inclusion criteria are a set of conditions that must be met in order to participate in a clinical trial. . We analyzed all births recorded in New York State hospitals from years 1994 through 2000. There were 1,871,594 births recorded during this time span. We excluded all births to New York City residents (885,685) and to out-of-state residents (3,324), and all plural births (35,144). Observations where data on baby's sex were missing and births where the recorded baby's birth weight was < 500 g or > 7,500 g (these values must be a result of miscoding) were also excluded (2,364). These exclusions produced a final sample size of 945,077 births. Statistical methods. We performed bivariate bi·var·i·ate adj. Mathematics Having two variables: bivariate binomial distribution. Adj. 1. analysis to look at the distribution of potential confounders between exposed (defined as residence in a PCB zip code) and unexposed groups (defined as residence in a zip code that doesn't have PCBs). Then two separate multiple logistic models logistic models, n.pl statistical models that describe the relationship between a qualitative dependent variable (that is, one that can take only certain discrete values, such as the presence or absence of a disease) and an independent variable. were fitted for two outcomes: low birth weight and very low birth weight. Low birth weight was defined as infants weighing between 1,500 and 2,500 g at birth, and very low birth weight was defined as infants weighing < 1,500 g. Finally, the model for probability of having a low-birth-weight baby was stratified stratified /strat·i·fied/ (strat´i-fid) formed or arranged in layers. strat·i·fied adj. Arranged in the form of layers or strata. by sex of the baby. Potential confunders and effect modifiers. Variables that have been reported to be independent risk factors for low birth weight/very low birth weight were considered potential confounders/effect modifiers in our regression models. The most important risk factor for the outcomes of interest is short gestational age. We input the number of completed weeks of gestation as a continuous variable in both models. The rest of the variables were categorized cat·e·go·rize tr.v. cat·e·go·rized, cat·e·go·riz·ing, cat·e·go·riz·es To put into a category or categories; classify. cat before being included in the model, and all are adjusted for gestational age. Mother's age was stratified into three groups: [less than or equal to] 18 years or younger, 19-39 years old, and [greater than or equal to] 40 years. Because paternal age has also been identified by some researchers (Abel et al. 2002) as a risk factor, a variable indicating father's age was included into the model and was classified as [less than or equal to] 18 years and [greater than or equal to] 19 years. The mothers were grouped by race into white, African American African American Multiculture A person having origins in any of the black racial groups of Africa. See Race. , and other. Mother's education was classified as less than or up through high school or having some postsecondary education. We used the lowest 10th percentile percentile, n the number in a frequency distribution below which a certain percentage of fees will fall. E.g., the ninetieth percentile is the number that divides the distribution of fees into the lower 90% and the upper 10%, or that fee level of distribution of mother's prepregnancy weight and mother's height in the study sample to define the cutoff point Cutoff point The lowest rate of return acceptable on investments. for low maternal weight before pregnancy and maternal short stature. They were found to be 110 lb for maternal weight and 61 inches for maternal height. We estimated parent's socioeconomic status on the basis of two variables: mean per capita income in the zip code of the mother's residence, and the primary payer for birth. The mean per capita income was classified as < $15,000 and [greater than or equal to] $15,000. The primary payers for birth were categorized as Medicaid/self-paid and other, which is expected to indicate parents of lower and higher socioeconomic status, respectively, because "other" is assumed to mean coverage by health insurance. The information on mother's smoking was obtained from the birth certificate and had two categories: yes/no. Single motherhood was defined as absence of any information on the father in the birth certificate. Results Among the total of 945,077 births, the PCB zip code group constituted 24.5% (231,583) and the non-PCB group was 75.5% (713,494) of the study sample. The mean birth weight in the PCB group was 3,386.7 g, whereas in the non-PCB group it was 3,408.3 g. The difference of 21.6 g was statistically significant, with a p-value < 0.0001. There was no significant difference in rates of very low-birth-weight infants between the two groups. The low-birth-weight rates were 5.7% and 5.0% and very low-birth-weight rates were 0.94% and 0.85% in the PCB group and non-PCB groups, respectively. The yearly distribution of low-birth-weight and very low-birth-weight rates showed a slight upward trend and followed the same pattern among the PCB and non-PCB groups (Figure 1). The upward trend is consistent with national statistics (Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. 1994). [FIGURE 1 OMITTED] Table 1 presents the distribution of potential confounders among the PCB and non-PCB groups. There was no difference in the sex ratio between the PCB and non-PCB sites. Several variables do have a different pattern of distribution between these two groups. The PCB-contaminated zip codes have a higher percentage of African-American population (13.4 vs. 9.6%), teenage mothers (6.9 vs. 4.6%), and teenage fathers (1.7 vs. 1%) and a higher percentage of people with mean per capita [Latin, By the heads or polls.] A term used in the Descent and Distribution of the estate of one who dies without a will. It means to share and share alike according to the number of individuals. annual income < $15,000 (28.5 vs. 18.9%) compared with the non-PCB group. There was also a larger proportion of women for whom Medicaid is the primary payer (32.4 vs. 24.5%). In addition, women in the PCB zip codes were less likely to have postsecondary education (49.6 vs. 56.4%) and more likely to smoke (18.7 vs. 14.2%) and to be single mothers (16.9 vs. 11.6%). The logistic regression models for both low and very low birth weight had 15 terms, including intercept. Overall, the fit of the model was good with concordance concordance /con·cor·dance/ (-kord´ins) in genetics, the occurrence of a given trait in both members of a twin pair.concor´dant con·cor·dance n. of 87% for the low-birth-weight model and 95% for the very low-birth-weight model. Table 2 shows the estimated odds ratios (ORs) for giving birth to an infant with low birth weight, with 95% confidence interval confidence interval, n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%. (CI) for each variable, calculated on the basis of the estimates of [beta]-coefficients and standard errors given by the model. The OR for weeks of gestation is not included in Table 2, because this variable was modeled as a continuous variable, and all other variables are adjusted for gestational age. However, gestational age was found to be a very significant risk factor for the outcome of interest. The OR for gestational age given by the model was 0.6, which means that each additional week of gestation lowers the risk of having a low-birth-weight baby by 1.7 times. Other risk factors for having a low-birth-weight baby in order from the strongest to the weakest are maternal smoking (OR = 2.08; 95% CI, 2.02-2.14), maternal weight before pregnancy < 110 lbs (OR 1.66; 95% CI, 1.61-1.71), African-American race of the mother (OR = 1.63; 95% CI, 1.58-1.68), female sex of the baby (OR = 1.43; 95% CI, 1.40-1.46), maternal age > 39 years (OR 1.38; 95% CI, 1.30-1.47), maternal height < 61 inches (OR = 1.29; 95% CI, 1.25-1.33), nonwhite non·white n. A person who is not white. non  white adj. race of the mother (OR = 1.29; 95% CI,
1.22-1.37), Medicaid or self-paid births (OR = 1.12; 95% CI, 1.08-1.14),
and teenage ([less than or equal to] 18 years) motherhood (OR = 1.08;
95% CI, 1.03-1.13). Living in zip codes contaminated by PCB waste sites
was found to be a weak but statistically significant risk factor for
having a low-birth-weight baby (OR = 1.04; 95% CI, 1.02-1.07). The
mother's educational and income level did not show a strong
association with the risk of having a low-birth-weight baby. Single
motherhood and young father's age seem not to have any effect on
the risk of having a low-birth-weight baby in our study sample.We then stratified the low-birth-weight model by the baby's sex. A mother's residence in a PCB zip code showed a statistically significant increased risk of giving birth to a low-birth-weight male infant (OR = 1.06; 95% CI, 1.02-1.10) but not for female infants (OR = 1.03; 95% CI, 0.99-1.07). Table 3 shows the estimated ORs with 95% CIs for the risk of having a very low-birth-weight baby for the same variables. There was no relation between PCB zip codes and very low-birth-weight infants for either sex (OR = 0.95; 95% CI, 0.88-1.02) or for nonwhite race of the mother or single motherhood. Several variables that were predictors of low birth weight remain strong risk factors for very low birth weight, including African-American race of the mother (OR = 1.60; 95% CI, 1.48-1.74), maternal height < 61 inches (OR = 1.59; 95% CI, 1.746-1.72), maternal weight < 110 lbs (OR = 1.39; 95% CI, 1.28-1.51), maternal smoking (OR = 1.25; 95% CI, 1.15-1.35), and female sex of the baby (OR = 1.22; 95% CI, 1.15-1.30). Interestingly, mother's age [less than or equal to] 18 years, low mother's educational level, and Medicaid or self-payment as the primary payer for births seem to exert a slight protective effect against the risk of having very low-birth-weight baby. Discussion Our results show that maternal residence in a zip code that contains or abuts a PCB-contaminated hazardous waste site results in a statistically significant 6% increased risk of giving birth to a male infant of low birth weight, after adjustment for other known risk factors. There was also a 3% increased risk of low birth weight for female infants, a value that almost reached statistical significance. These results suggest that simply living near a PCB-contaminated site poses a risk of exposure and of health impact, probably secondary to airborne spread of the PCBs. Although many PCB-contaminated sites also have other types of contaminants present, the disproportionate impact on male infants supports the conclusion that it is the PCBs that are responsible. A selective effect of PCB or dioxin/furan exposure on male infants has previously been reported in several other studies (Rylander et al. 1995, 1996; Vartiainen et al. 1998; Hertz-Picciotto et al. 2000). Limitations. The main limitation of this study is the exposure assessment. The exposure was measured on a group level that cannot correctly represent the true level of individual exposure. Very little is known about the extent to which residents living near a waste site are exposed to PCBs (Stehr-Green et al. 1988). In general, the use of surrogate measures such as residence close to a waste site can lead to nondifferential misclassification of exposure and decrease the sensitivity of the study to find a true effect (Vrijheid 2000). Moreover, exposure to PCBs from landfills or contaminated bodies of water, if such exposure exists, would be expected to be at very low concentrations. Associations with such low-level environmental exposures in the general population are by their nature hard to establish. Low-dose exposures are generally expected to generate small increases in relative risk that will be difficult to distinguish from noise introduced by confounding confounding when the effects of two, or more, processes on results cannot be separated, the results are said to be confounded, a cause of bias in disease studies. confounding factor factors and biases. Another potential source of exposure misclassification involves the assumption that the zip code at the time of birth reflects the residence where a woman lived before and during the critical period of her pregnancy. If a woman moved during pregnancy, then the zip code of her latest residency does not represent her exposure status. It appears that as many as 25% of women change residence between conception and the end of the first trimester Noun 1. first trimester - time period extending from the first day of the last menstrual period through 12 weeks of gestation trimester - a period of three months; especially one of the three three-month periods into which human pregnancy is divided (Khoury et al. 1988; Shaw and Malcoe 1991; Shaw et al. 1992). This type of misclassification error is also nondifferential with respect to outcome and tends to reduce the magnitude of the estimated effects (Copeland et al. 1977; Shaw et al. 1992). Information on exposure and confounders derived from birth certificates is not always accurate and complete. Almost all study variables have some percentage of missing data. For some variables this percentage was relatively low (0.5% for race, 0.3% for mother's age, and 1.7% for mother's education and smoking). For other variables the percentage of missing data was higher (3.2% for gestational age, 6.9% for maternal prepregnancy weight, and 10% for maternal height). If the data are randomly missing, it does not distort the effect estimates but could affect the standard error. We also cannot rule out some percentage of data miscoding. With respect to potential confounders, we were limited to those that are present on the birth certificate. Several other variables in the birth certificate, such as maternal alcohol and drug use and mother's comorbid conditions, were not included in our analysis because these variables had a high percentage of missing and miscoding data. Although we cannot completely rule out a contribution of these and possibly other unknown confounders, the fact that the relationship between low birth weight and PCB sites was stronger for male than for female infants supports the conclusion that PCB exposure was the critical factor. No evidence indicates that other confounders would selectively affect male infant birth weight. Overall, our results confirm previous observations on a number of risk factors for giving birth to an infant with low/very low birth weight. PCBs and low birth weight. We have found that infants born to mothers who reside in PCB-contaminated zip codes give birth to infants who are on average 21.6 g lighter than those born to mothers who do not live in PCB-contaminated zip codes. This value should be compared with the reports of Fein et al. (1984), who found that mothers who ate contaminated Lake Michigan fish had infants 160-190 g lighter than those of controls, and of Taylor et al. (1984), who reported that women occupationally exposed to PCBs have infants 153 g lighter than those of controls. After adjustment for most known confounders, we find that maternal residence in proximity to waste sites contaminated by PCBs increases by 6% the risk of having a low-birth-weight male baby, whereas the risk of having a low-birth-weight female infant narrowly misses being significant, and there is no elevated risk of having a very low-birth-weight baby of either sex. Even though the added risk of giving birth to low-birth-weight male babies by women residing in proximity to PCB-contaminated zip codes is small, the observation is consistent with the hypothesis that living next to a PCB-contaminated site constitutes a risk of exposure and of adverse health effects. The sex-specific effect is important support for the conclusion that the risk is due to PCB exposure, because most other confounders are not known to exhibit selective effects on male infants, and we have controlled for the added general risk of low birth weight in female infants. Several points are worth noting. We have no direct exposure assessment other than zip code of residence. Zip codes are of irregular shape, and residence in a zip code near a PCB site is certainly not the optimal indicator of exposure. Previous studies of this type (Shaw et al. 1992; Sosniak et al. 1994) found that merging a large population database with environmental data is an innovative but not very efficient method of assessing the risks of low birth weight related to the environment. On the other hand, the benefits of such investigations are that they are economical, they may be useful for identifying large risks not previously known, and they may be used as hypothesis-generating studies (Shaw et al. 1992). Use of birth records for a large geographic area such as New York State over several years provides sufficient power to detect relationships that would otherwise not be apparent. Furthermore, the inadequacy of the exposure assessment should obscure the relationship, which suggests that the true relationship between PCB exposure and low birth weight of male infants (and probably female infants as well) is actually greater than we have demonstrated. To identify the risk of maternal residence in selected zip codes, more detailed studies measuring the actual serum level of PCBs in women living in these zip codes are needed. If living in a PCB-contaminated zip code indeed poses a risk of low birth weight in male infants, there is a question of the route of exposure to the mother. Consumption of PCB-contaminated fish is the best-documented route of exposure (Fein et al. 1984; Jacobson JL et al. 1990; Jacobson SW et al. 1985; U.S. Department of Health and Human Services Noun 1. Department of Health and Human Services - the United States federal department that administers all federal programs dealing with health and welfare; created in 1979 Health and Human Services, HHS 2000), but sport fishers are not defined by the zip code in which they live. The most likely route of exposure is airborne (Currado and Harrad 1998), either through inhalation of volatile PCBs or PCBs bound to particulates or through ingestion ingestion /in·ges·tion/ (-chun) the taking of food, drugs, etc., into the body by mouth. in·ges·tion n. 1. The act of taking food and drink into the body by the mouth. 2. of PCB-contaminated particulates with foodstuffs foodstuffs npl → comestibles mpl foodstuffs npl → denrées fpl alimentaires foodstuffs food npl → . Inhalation as a route of exposure has not received much attention, but there is considerable evidence that PCBs volatize, especially from contaminated bodies of water (Chiarenzelli et al. 2000) and wet sediments (Bushart et al. 1998; Chiarenzelli et al. 1996). Volatile PCBs can be absorbed through inhalation (Casey et al. 1999). PCBs are widely distributed Adj. 1. widely distributed - growing or occurring in many parts of the world; "a cosmopolitan herb"; "cosmopolitan in distribution" cosmopolitan bionomics, environmental science, ecology - the branch of biology concerned with the relations between organisms in the food chain (U.S. Department of Health and Human Services 2000), and even remote places will have measurable PCBs in the air (Lohmann et al. 2001). Therefore, there is no unexposed population, and our results reflect only the effects of gradients of exposure. This fact also suggests that the risks of low birth weight that we have demonstrated are underestimations of the actual risk. We did not find as strong a relationship between residence in a PCB-contaminated zip code and gestational age as others have reported (Fein et al. 1984; Taylor et al. 1984, 1989), who have suggested that gestational age is the major cause of low birth weight after PCB exposure. The reason for this is not clear, but it most likely reflects a lack of accuracy in the reporting of gestational age (from last menstrual period last menstrual period Gynecology The most recent time that a ♀ notes menstruation, a datum recorded in a chart during a routine gynecologic visit. See Menstruation. ) in the vital statistics database. Animal studies have demonstrated that PCBs stimulate contraction of pregnant rat uterine uterine /uter·ine/ (u´ter-in) pertaining to the uterus. u·ter·ine adj. Of, relating to, or in the region of the uterus. muscle (Bae et al. 1999a, 1999b), which is likely the mechanism by which PCBs cause a shortened gestational age. It is interesting that this is a property of lower chlorinated chlorinated /chlo·ri·nat·ed/ (klor´i-nat?ed) treated or charged with chlorine. chlorinated charged with chlorine. chlorinated acids some, e.g. , non-dioxin-like congeners, not the dioxin-like congeners (Tsai et al. 1996). Such congeners are more volatile and less persistent, but still may have health effects. A separate issue raised by the present study is the inequity of locating hazardous waste sites and hazardous materials. The analysis of distribution of potential risk factors for giving birth to a low-birth-weight/very low-birth-weight baby indicates that the PCB group has a higher risk not only because of proximity to waste sites but also because of race and income level (Table 1). This means that hazardous waste sites and the locations of hazardous materials are either disproportionately situated near minority communities, especially African-American communities and low-income communities, or that such places are unattractive to those who can afford to choose to live elsewhere. These studies have confirmed several known risk factors for low birth weight and have also found 6% increased risk associated with living near a PCB-contaminated site and giving birth to a male infant of low birth weight. Because low birth weight is itself a risk factor for infant morbidity and mortality and a number of chronic diseases in adulthood, even a small increased risk has important public health implications. Furthermore, because zip code of residence is an inexact exposure assessment, it is likely that our results significantly underestimate the true risk from PCB exposure. Perhaps the most significant conclusion from these observations is that they provide additional support for the hypothesis that simply living near a PCB-contaminated site is a risk of exposure and of adverse health effects. The fact that the relationship was found only for male infants is consistent with this effect being secondary to PCB exposure, because most other confounders are not known to have a sex-specific effect.
Table 1. Distribution of potential confounders between exposed
and unexposed groups.
PCB-contaminated sites
Variable No. Percent
Sex of babies
Male 118,909 51.3
Female 112,674 48.7
Race
White 192,191 83.5
African American 30,955 13.4
Other 7,091 3.1
Length of gestation (weeks)
< 37 20,080 9.0
[greater than or equal to] 37 204,193 91.0
Mother's age (years)
[less than or equal to] 18 16,009 6.9
19-39 210,214 90.9
[greater than or equal to] 40 4,987 2.2
Father's age (years)
[less than or equal to] 18 3,178 1.7
[greater than or equal to] 19 188,484 98.3
Mother's education
No education 308 0.1
High school only 114,267 50.5
Postsecondary education 112,543 49.6
Mother's weight before pregnancy (lbs)
< 110 16,686 7.7
[greater than or equal to] 110 200,325 92.3
Mother's height (inches)
< 61 17,043 7.9
[greater than or equal to] 61 198,866 92.1
Average annual per capita income in the ZIP code of residence
$0-15,000 60,058 28.5
$15,000-34,999 161,124 69.6
[greater than or equal to] $35,000 4,401 1.9
Primary payer for birth
Medicaid 72,965 32.4
Self-paid 3,861 1.7
Other 148,517 65.9
Mother's smoking
Yes 42,899 18.7
No 186,540 81.3
Single motherhood
Yes 39,222 16.9
No 192,361 83.1
PCB-free sites
Variable No. Percent
Sex of babies
Male 365,000 51.2
Female 348,494 48.8
Race
White 618,065 87.0
African American 68,482 9.6
Other 23,698 3.3
Length of gestation (weeks)
< 37 56,919 8.2
[greater than or equal to] 37 634,062 91.8
Mother's age (years)
[less than or equal to] 18 33,042 4.6
19-39 658,534 92.6
[greater than or equal to] 40 19,511 2.7
Father's age (years)
[less than or equal to] 18 6,516 1.0
[greater than or equal to] 19 621,591 99.0
Mother's education
No education 618 0.1
High school only 305,323 43.5
Postsecondary education 396,023 56.4
Mother's weight before pregnancy (lbs)
< 110 49,737 7.5
[greater than or equal to] 110 612,758 92.5
Mother's height (inches)
< 61 46,342 7.3
[greater than or equal to] 61 587,274 92.7
Average annual per capita income in the ZIP code of residence
$0-15,000 134,493 18.9
$15,000-34,999 532,262 73.3
[greater than or equal to] $35,000 55,718 7.8
Primary payer for birth
Medicaid 167,970 24.5
Self-paid 13,599 2.0
Other 505,170 73.6
Mother's smoking
Yes 99,502 14.2
No 599,910 85.8
Single motherhood
Yes 82,471 11.6
No 631,023 88.4
Table 2. Estimated ORs (95% Cls) for risk of having low-birth-weight
babies.
Variables (a) OR (95% CI)
PCB 1.04 (1.02-1.07)
Female sex of the baby 1.43 (1.40-1.46)
African-American race of the mother 1.63 (1.58-1.68)
Nonwhite race of the mother 1.29 (1.22-1.37)
Mother's age [less than or equal to] 18 years 1.08 (1.03-1.13)
Mother's age > 39 years 1.38 (1.30-1.47)
Father's age [less than or equal to] 18 years 1.01 (0.92-1.12)
Mother's educational level less than or equal to
high school grades 1.06 (1.04-1.09)
Parents annual per capita income < $15,000 1.03 (1.00-1.06)
Medicaid/self-paid births 1.12 (1.08-1.14)
Maternal weight before pregnancy < 110 lbs 1.66 (1.61-1.71)
Maternal height < 61 inches 1.29 (1.25-1.33)
Single motherhood 1.04 (0.95-1.14)
Maternal smoking 2.08 (2.02-2.14)
(a) All variables are adjusted for gestational age (in weeks).
Table 3. Estimated ORs (95% CIs) for risk of having very
low-birth-weight babies.
Variables (a) OR (95% CI)
PCB 0.95 (0.88-1.02)
Female sex of the baby 1.22 (1.15-1.30)
African-American race of the mother 1.60 (1.48-1.74)
Nonwhite race of the mother 0.98 (0.81-1.17)
Mother's age [less than or equal to] 18 years 0.81 (0.71-0.93)
Mother's age > 39 years 1.16 (0.98-1.37)
Father's age [less than or equal to] 18 years 0.94 (0.73-1.21)
Mother's educational level less than or equal to
high school grades 0.90 (0.83-0.96)
Parents annual per capita income < $15,000 1.08 (1.00-1.17)
Medicaid/self-paid births 0.88 (0.81-0.95)
Maternal weight before pregnancy < 110 lbs 1.39 (1.28-1.51)
Maternal height < 61 inches 1.55 (1.46-1.72)
Single motherhood 0.79 (0.66-1.10)
Maternal smoking 1.23 (1.15-1.35)
(a) All variables are adjusted for gestational age (in weeks).
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E-mail: Carpent@uamail.albany.edu This research was supported by funds received from the Fogarty International Center, grant 5D343TW0063607, and the Muskie mus·kie or mus·ky n. pl. mus·kies The muskellunge. Freedom Support Act Fellowship Program. The authors declare they have no conflict of interest. Received 11 October 2002; accepted 17 March 2003. |
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