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Toxicity
According to the material safety data sheet (MSDS) for this chemical, the lowest dose observed to be fatal in humans was 200 mg per kg of body weight in women and 429 mg per kg of body weight in men. The lethal dose in rats is rather higher; 2,660 mg per kg of body weight was the lowest dose that would kill 50 percent of the rats to whom it was administered.
EU Findings
Boric acid is listed in Table 3.1, Annex VI of European Commission Regulation2/2008 and Table 3.2 of the same, as a substance with reproductive toxicity. The EU has found that boric acid is poorly absorbed through the skin but rapidly and completely absorbed if ingested. It's rapidly excreted, although it has a longer half-life in humans than in mice and rats. Past evidence from a poisoning case involving a pregnant woman suggests that boric acid can indeed cross the placenta and therefore impact the developing fetus.
Effects on Fertility
Based on past studies in mice, rats and beagles, the EU has concluded that the testes are one of the two major targets impacted by exposure to boric acid. The no-observed-adverse-effect level (NOAEL) (the highest dose at which no effects were observed) was 17.5 mg per kg of body weight per day in rats. Multigeneration studies found that rats fed high doses of boric acid were unable to reproduce successfully, and male rats in these groups exhibited atrophied testes; these studies suggested that boric acid adversely impacted the female reproductive system as well.
Developmental Toxicity
Studies cited by the European Commission found that boric acid caused developmental toxicity in mice, rats and rabbits. Mid-level doses not lethal to the mother caused reduction in birth weight and skeletal malformation in pregnant rats and mice. Rabbits exhibited signs of cardiovascular malformation. The estimated NOAEL in rats was 9.6 mg per kg of body weight per day. The data on effects in humans is limited and not sufficient to draw any conclusions, but based on the animal studies, the European Commission believes that boric acid has the potential to cause developmental toxicity.