Case study V: Retrospective Cohort Study of the Association of Congenital Malformations and Hazardous Waste.

Adapted from Geschwind, S.A.; Stolwijk, J.A.J.; Bracken, M.; et al. Risk of congenital malformations associated with proximity to hazardous waste sites. Am J. Epidemiol. 1992; 135(11):1197-1207.

Congenital anomalies or malformations are difficult to pinpoint as to cause. Some congenital malformations cause are understood, many are not. Cause may be single isolated cases, whereas others are multiple and varied. Some malformations at birth are inherited, and some are sporadic in their manifestation. Congenital defects are sometimes apparent and sometimes hidden, taking years to become obvious. About 10% of neonatal deaths are caused by congenital malformations. A major malformation is apparent at birth in 3-4% of newborns. By the fifth year, up to 7.5% of all children manifest a congenital malformation. The incidence of certain congenital malformations varies with the defect (Cleft lip occurs at the rate of 1 per 1000 births in the United States). Interfamily marriage and culture practices can contribute to congenital malformations, as can perinatal problems and environmental exposures. Genetic factors are responsible for many congenital abnormalities and syndromes. Drugs taken while pregnant, infectious agent, and irradiation are known to cause birth defects. Chemicals in the environment, and exposure to hazardous materials and waste in the environment, and exposure to radiation in the worksite or environment have also been implicated (source: Berkow R, ed. The Merck Manual, 14th ed. Rahway, NY: Merck and Company; 1982).

Case on Congenital Malformations Associated with Proximity to Hazardous Waste Sites.

Much concern has been expressed by the general public and public health scientist alike over the effect of exposure to environmental pollutants and how they have increased in modern society. It remains unclear whether chronic exposure to toxic chemicals in the environment is present in sufficiently high doses to produce adverse medical effects in humans. Inadvertent exposure to hazardous waste such as Love Canal (a neighborhood in Niagara Falls, New York, located in the white collar LaSalle section of the city) has increased concern about any adverse effects the exposure might have on reproductive health. It also remains unclear whether individuals who live near toxic chemical waste sites receive doses in sufficient amounts to pose a health hazard, especially to reproductive functions. One concern is that many toxic chemicals present in toxic waste landfills and hazardous waste sites are cytotoxic. That is, they affect cells, tissues, and organs at specific stage of development and inhibit or interfere with normal growth, especially in embryo and fetus growth, as well as development stages.

High rates of birth defect have been reported in children exposed to mercury, solvents, and certain toxic chemicals. Community-based studies have been conducted based on reports of clustering of disease around hazardous waste site. Rarely have congenital defects in infants born to exposed parent been well documented.

This study uses a four-tiered hypothesis approach in order to evaluate the relationship between birth defects and the potential exposure to toxic waste sites: (1) Does residential proximity to a waste site when pregnant increase risk of bearing a child with a defect? (2) Do defects of specific organ systems correlate with proximity to a toxic waste site? (3) Were defects associated with off-site migration of chemicals? How does the epidemiologist clarify whether this increases potential health risk? (4) Have chemical types associated with certain organ system defects been evaluated?

Pesticides have been associates with oral cleft (lip or palate), or musculoskeletal defects, heavy metals with nervous system defects, solvents with nervous system defects or digestive system defect, and plastic with chromosomal anomalies. Do the later phases corroborate the initial finding? Finally, this study’s aim was to test the association of environmental and health data bases on geographic mapping methods for ascertaining environmental exposures.

Database of New York State Department of Health were used: Congenital Malformations Registry (CMR) and the Hazardous Waste Site Inspection Program. The two programs were linked together for analysis of the four tiers of hypothesis. The CMR includes reports for all congenital malformations for the state’s hospitals, medical facilities, and private physicians diagnosed in children up to 2 years of age. In the state of New York, 917 waste sites in 62 counties were available. New York City sites as well as several other sites were eliminated due to inadequate information. For final study, 590 waste sites in 20 counties were used. Epidemiological map study approach included each site being assigned a longitude and latitude using EPA and New York Department of Environmental Conservation records.

A total of 34,411 cases of malformations were recorded in the CMR for the years 1983-1985 and 1984-1986 birth cohorts. Any cases that were unusual were eliminated: multiple birth, redundant cases, and CDC exclusions list to avoid misclassification of malformations, census mapping coordinates missing, addresses incomplete, and locations without a census tract. The study was based on 12,442 congenital malformations and 9,313 cases. One case could have more than one defect.

Eight categories of malformations were used from ICD-9-CM that has been reported by research studies in the literature as being associated with exposures to chemicals or toxics substances (see Table I-11). Each individual exposure was unknown, and each could have had multiple exposures to a complex mix of chemicals. All case were put under one general analysis. Each case was then placed in one of the eight categories and analyzed. More than one defect was found present in each case.

TABLE I-11 Eight Categories of Malformations ICD-9-CM

Oral cleft defects

Musculoskeletal defects

Nervous system defects

Integument defects

Digestive system defects

Chromosomal anomalies


Remaining defects without category

Data from ICD-9, International Classification of Diseases, 9th revision

Controls were selected from birth certificate records: 17,802 or 12% of the 506,183 live births for 1983-1984 in the State of New York. Cross-checks were made to assure no congenital malformations were included in the control. Confounding variables were excluded from both cases and controls, and information included the following:

· Maternal age

· Parity

· Race

· Birth weight of the child

· Education

· Length of gestation

· Address and county of residence

· Gender of the child

· Any pregnancy complications

Address for cases and controls were each assigned a latitude and longitude. Coordinates were taken from census block base on Standard Metropolitan Statistical Areas, and Postal Carrier Route centroids (a centroid is the center point of the Postal Carrier Route boundary); zip code centroids were used. A sample of 500 addresses was taken at random as a test of the mapping methods. The mapping procedure was accurate within 200 feet, 80% of the time.

Hazardous waste sites were assessed using the Hazardous Waste Site Inspection Program (HWSIP), which estimates the likelihood of human exposure. Possible exposure routes into humans include inhalation, ingestion, and dermal contact, which occur by environmental exposure transmission from air, groundwater, surface, water, or soil. This study included all the residents within a 1-mile radius of the waist site edge. Still, absolute risk of exposure was uncertain. Assessment was based on a set of score of a variety of factors: chemical exposure, a probability score chance of contaminant transport from the site, a target factor score that accounts for the population and distance from the waste site, and a weighting factor score giving each exposure a level of relative importance. The assessment exclude the total population portion of the target factor score to give greater weight to the residents surrounding the waste sites.

Five categories of chemicals grouped by chemical properties were developed.

The five categories were as follow:

· Pesticides

· Metals

· Solvents

· Plastics

· Unknown

An exposure risk index was completed for each case. The index accounted for distance and hazard ranking score within a 1-mile radius of the birth residence. Waste sites based on evidence of off-site migration of contaminants were separated from non-migration sites.

All case and control coordinates were matched to hazardous waste sites by a matching program. Distance and direction from the hazardous waste site for the residence of each case or control living within a 1-mile radius of the edge of the site were considered potentially exposed. Risk was determined by association between mother’s (maternal) proximity to waste site and presence of congenital anomalies (Birth defects).

A 12% increase risk for defects associated with maternal proximity to toxic waste site was found. Odds ratios were used to assess the association between proximity to toxic sites and material residence. An odds ratios score above 1.01 shows a positive association and the higher the score the stronger the association. Table I-12 presents the odds ratios for congenital malformations with residential proximity to select hazardous waste sites. Table I-13 present odds ratios and exposure risk index for all congenital malformations and for three specific body systems affected by documented chemical leaks at hazardous waste sites. Table I-14 presents odds ratios for congenital malformations for all infants with specific malformations and residential proximity to selected waste sites and chemical groups.

Table I-12 Odds Ratios for All Congenital Malformations and for Specific Malformations in Infants with Residential Proximity to Selected Hazardous Waste Sites, New York State, 1983-1984.

Number of Cases͙͙ ͙‡

Congenital Malformation (s)

Odds Ratios+§


All malformations combined



Nervous System



Musculoskeletal System



Integument System



Oral Cleft



Digestive System



Chromosomal anomalies



Syndromes ǁ



Other(data too limited to infer associations with chemical exposure)



+Data from ICD-9, International Classification of Diseases, 9th revision

‡The numbers of cases for the individual organ systems do not add up to the total number of cases for all defects combined because individuals may had more than one defect.

§Adjusted for maternal age, race, education, complications during pregnancy, parity, population density for county of residence, and gender of the child, by logistic regression.

ǁ Syndromes include all defects codes as “syndrome” in the New York State Congenital Malformations Registry, or any child with four or more defects.

Table I-13 Odds Ratios and Exposure Risk Index for All Congenital Malformations and for Three specific Body Systems Affected by Documented Chemical Leaks at Hazardous Waste Sites


All Malformations Combined (740-759)

Nervous System (740-742)

Musculoskeletal System (754-756)

Integument System (757)

Exposure Risk Index___

No exposure risk





Low exposure risk









High exposure risk









Chemical Leaks_______

No expose





Exposed, but no leaks found at site









Exposed, and leaks found at site










†Adjusted for maternal age, race, education, complications during pregnancy, parity, population density for county of residence, and gender of the child, by logistic regression.

‡ Data from ICD-9, International Classification of Diseases, 9th revision

§Numbers in parentheses, 95% confidence interval

Table I-14 Odds ratios for Congenital malformations for All infants with Specific Malformation Codes† and Residential Proximity to Selected Toxic Waste Sites Containing Associated Chemical Groups: New York State, 1983-1984.

Chemical and Associated Malformation (Reference)



Pesticides/Oral cleft (13-15)



Pesticides/Musculoskeletal (16, 17)



Metals/Nervous system (18-20)



Solvent/Nervous system (21-23)



Solvent/Digestive System (24,25)



Plastics/Chromosomal anomalies (26-29)




†Previously related to chemical exposure in the literature.

‡ Data from ICD-9, International Classification of Diseases, 9th revision; or = odds ratios, CI=confidence interval.

§Adjusted for maternal age, race, education, complications during pregnancy, parity, population density for county of residence, and gender of the child, by logistic regression.

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