Here’s the latest new information from the federal government’s National Toxicology Program on its ongoing investigation of the Elk River chemical spill:
The National Toxicology Program (NTP) evaluated the potential maternal and prenatal toxicity of MCHM, the primary chemical spilled into the West Virginia Elk River. This update is a follow-‐up to the December 2014 NTP Update,2 which reported the results of a preliminary study used to design this more comprehensive main study. The main study evaluated the effects of MCHM on maternal health and embryo and fetal development in rats following oral administration of MCHM at doses of 50, 100, 200, and 400 mg/kg/day. NTP found that MCHM decreased fetal weight and induced malformations in fetuses in the highest dose group of 400 mg/kg/day. A small decrease in fetal weight was observed in the 200 mg/kg/day dose group, which is similar to the small decrease in fetal weight observed in the 150 mg/kg/day dose group of the preliminary study.
At these dose levels, exposure to MCHM had no effect on maternal or fetal survival, and minimal effects were observed in maternal clinical pathology. The magnitude of these responses was small and not considered to adversely impact the health of the pregnant rat or the fetuses. Fetal weight was decreased significantly by 15 percent at 400 mg/kg/day, and a small decrease in fetal weight was observed in the 200 mg/kg/day dose group, which is consistent with the decrease in the 150 mg/kg/day dose group of the preliminary study. There were also increases in specific malformations in the 400 mg/kg/day group. The malformations included extra ribs in the lumbar and cervical region of the fetus and decreased fusion of cartilage to the sternum. Although not considered a malformation, increases in unossified (non-‐mineralized bone) or incomplete ossification (partially mineralized bone) of the sternebrae (bones of the sternum) and vertebrae were observed in fetuses in the 400 mg/kg/day dose group. These effects on ossification are consistent with the decreased fetal weight, indicating delayed fetal growth.
And the conclusion?
Taken together, these results show MCHM is a developmental toxicant in the absence of significant maternal toxicity and indicate that the developing fetus is more sensitive than the dam to MCHM exposure. The finding that MCHM is toxic to the developing rat fetus does not establish that it would cause similar effects in humans. Many factors determine whether toxicity in animal studies translate to similar effects in humans, such as the amount and duration of exposure, differences in how the human body handles the chemical compared to other species, and whether the biological basis for the effect is similar between different species and humans.
Researchers are scheduled to update the National Toxicology Program’s Board of Scientific Counselors on their work during a meeting on Tuesday. The meeting is scheduled to be webcast.