Months after the sarin nerve agent attacks in Syria, we are now confronted, on Twitter and in The Telegraph and The Daily Star, with stories and images of babies being born with deformities and defects, allegedly caused by sarin exposure. But what do we know about whether sarin causes birth defects? In the last few weeks, many people have asked me these questions, and it has forced me to closely examine the available scientific literature. This literature is not extensive, but there are dozens of articles and books that do address the subject. On the whole, the available literature seems to show that sarin does not cause birth defects.
Before addressing the conclusion, it is important to examine the question of whether these babies were affected by sarin from the broader perspective of birth defects in general. In the United States, a generally healthy country, one report is that one baby in 33 is born with some sort of defect or abnormality, although exact definitions and statistics vary. This baseline rate is somewhat higher in many developing countries, including a reported prewar (2006) rate of 7.48% for Syria. Even if we could confirm that the mothers in question were exposed to sarin, how do we know that these specific babies wouldn’t have had defects without the presence of sarin? It is also important to understand that birth defects come from many causes. Exposure to teratogens, agents or substances that cause birth defects, is only one of many different possible causes. According to the Encyclopedia of Toxicology, as much as 79% of birth defects are of unknown cause and only 6% are from teratogens. While it is easy to see that any individual case may be lost in the general background noise of generally expected birth defects, this does not exclude sarin as a teratogen.
But do we know if sarin is a teratogen? The vast majority of human exposures, either deliberate or accidental, are among adult men, not pregnant women. But the subject has been studied. The canonical textbook in the field, Medical Aspects of Chemical Warfare, has very little to say, despite addressing sarin at great depth. Other works do not believe sarin or other military nerve agents are teratogens, including Dr. Ramesh Gupta’s Handbook of Toxicology of Chemical Warfare Agents and Dr. James Romano’s encyclopedic Chemical Warfare Agents: Chemistry, Pharmacology, Toxicology, and Therapeutics, despite exhaustive explorations. However, since deliberately exposing humans, let alone pregnant women, is well beyond morality and ethics, science can look to animals for some evidence. Much of the existing literature up to the early 1990s was well summarized by Dr. Nancy Munro in an excellent 1994 article. Munro had access to US government studies for this article and references a study of rats and rabbits where sarin caused no fetal malformation, even at doses high enough to kill the mother. Another study showed chronic exposure of low levels of sarin in rats having no discernable link to birth defects. A more recent study exposed chicken eggs to various levels of sarin and studied the development of the eggs and chicks, concluding that sarin did not increase incidence of malformations. The resulting chicks did have some neurological impairment, but no physical abnormalities.
Some studies have occurred with closely related chemicals, such as the nerve agent VX. VX, although having different physical characteristics, acts through the same biochemical mechanisms as sarin. A large accidental exposure of sheep to VX occurred in Utah in 1968 which, although a debacle for the US government, gave rise to the interesting Van Kampen veterinary study that showed that, at least in sheep, no birth defects were noted.
The few large sample populations of humans exposed to sarin that do exist are in Japan, Iraq, and Iran. Studies in Japan, both for the small 1994 Matsumoto incident (here and also here) and the larger 1995 Tokyo incident make no reference to birth defects or reproductive effects. Dr. Ohbu’s article on the Tokyo exposure is as close as we get in modern scientific literature to addressing this issue directly. Four women were pregnant when they were exposed to sarin in Tokyo; all four delivered normal babies.
Iran represents another pool of affected population to study. At least 700 tons of nerve agents were used by Iraq in the Iran-Iraq war. I consulted with Dr. Shahriar Khateri, an Iranian expert who studies the long-term effects of chemical warfare upon members of the Iranian population. Khateri told me that Iranians could find no link between nerve agent exposure and birth defects, though he stresses that more research is needed in this area of inquiry.
Since sarin is chemically related to pesticides in the organophosphate family, perhaps studies there can shed some like. Leiken and Mcfee’s Handbook suggests that malathion might cause birth defects (while also categorically saying the military nerve agents do not), but Dr. Jan Storm, in Patty’s Toxicology, states that “organophosphate pesticides have generally not shown reproductive or developmental effects in animal studies.” Several authorities point out a number of reasons why organophosphate pesticides differ from their nerve agent cousins in regard to long-term biological effects, including Dr. Romano’s work cited above.
One might also ask about whether sarin affects the offspring of men exposed to it. Dr. William Page studied this as part of long cohort study of military volunteers exposed to chemical agents from 1955 to 1975. This study showed no substantial difference in birth defect rates between men exposed to chemical warfare agents and those not exposed.
Finally, what about antidotes? Perhaps atropine, the principal sarin antidote could be to blame? At least according to B. Bailey and Mosby’s Drug Consult, the latter of which speaks of exposing rats to absurdly high doses out of proportion to nerve agent treatment, atropine is probably not a culprit in birth defects.
The basic conclusion to be had here is that a number of people with far more specialized knowledge than mine have studied the possibility and think that sarin probably does not cause birth defects. Of course, the possibility cannot be completely excluded, but it seems quite unlikely that the reported births in Syria are (a) different somehow from the expected baseline (b) not caused by something else and (c) caused by sarin exposure. While I have every sympathy for the mothers and children, it seems to me that there is every risk that tragic events are being exploited for political purposes in this instance. Sarin is bad and should never be used, but to blame it for deformed babies in contravention of the published science seems wrong to me.