Case Report

We identified the subject during her participation in a research study to evaluate sources and exposures to environmental chemicals in pregnant women and their infants. English- and Spanish-speaking patients in their third trimester were recruited from the prenatal clinic at San Francisco General Hospital (San Francisco, CA), and consented to provide samples of maternal whole blood and umbilical cord blood, as well as environmental exposure and demographic information. After collection, Biomonitoring California, state-level biomonitoring program, analyzed the biologic samples for several environmental chemicals, including mercury.

The laboratory analysis showed that 1 participant out of 77 had unusually high levels of mercury. Her blood mercury level was 15.16 μg/L, nearly 3 times higher than the early reporting threshold of 5.8 μg/L used by the Centers for Disease Control and Prevention. The concentration of mercury in umbilical cord blood was also above 5.8 μg/L (7.43 μg/L). Because mercury exposure of this magnitude poses a risk to the developing central nervous system and the kidneys, we conducted a follow-up investigation to identify the exposure source. The study obstetrician met with her during the 6-week postnatal appointment to administer a questionnaire about symptoms, potential sources of mercury exposure at home, at work, and to obtain a urine sample. During the interview, the patient did mention that she ate a considerable amount of Mojarra (tilapia) purchased from a local market. Fish are a common source of environmental mercury, and the tilapia, although generally considered a low mercury containing fish, could potentially have contributed to the participant’s high levels. We purchased and analyzed a sample of tilapia from the same market but we found that it had minimal levels of mercury. Participant’s urine, which was collected during the postnatal interview, had a total mercury level of 40 μg/L; a form commonly found in batteries, disinfectants, and cosmetic creams. Based on the results of these 2 analyses, we concluded that tilapia was not the source of mercury.

After consultation with the University of California San Francisco Pediatric Environmental Health Specialty Unit, we scheduled a home visit to further investigate the source of exposure. Using a Lumex Portable Mercury Analyzer (Ohio Lumex Co., Twinsburg, OH), the team detected mercury vapor in the participant’s bathroom at concentrations above 11,000 ng/m ³ , particularly near 2 jars of face cream. A typical background concentration of mercury vapor is 20 ng/m ³ . The participant indicated that the creams had been purchased at a pharmacy in a small town in the Mexican state of Michoacán, had been enriched with folic acid, red oxide, vitamin E, and eucalyptus, among other ingredients, in both powder and oil form, and were brought into the US by a relative. The creams contained 21,000 ppm and 30,000 ppm of mercury, respectively. The Food and Drug Administration’s standard for mercury in face cream products is <1 ppm. The adulterated creams were removed from the participant’s home. Because the participant was lost to follow-up, we have been unable to assess the impact of this intervention on her and her infant’s mercury levels. This case of mercury poisoning emphasizes the need for maternal and child screening for heavy metals such lead and mercury and other neurotoxicants.