Inorganic borates, including boric acid, Na, ammonium, K, and Zn borates generally display low acute toxicity orally, dermally, and by inhalation. They are either not irritant or mild skin and eye irritants. Exceptions owing to physiochemical properties do occur. Longer-term toxicological studies have been reported mainly on boric acid or borax where the properties are generally similar on an equivalent boron (B) basis. The critical effects in several species are male reproductive toxicity and developmental toxicity. The doses that cause these effects are far higher than any levels to which the human population could be exposed. Humans would need to consume daily some 3.3 g of boric acid (or 5.0 g borax) to ingest the same dose level as the lowest animal NOAEL. No effects on fertility were seen in a population of workers exposed to borates or to a population exposed to high environmental borate levels. There is remarkable similarity in the toxicological effects of boric acid and borax across different species. Other inorganic borates that simply dissociate to boric acid are expected to display similar toxicity, whereas those that do not dissociate simply to boric acid may display a different toxicological profile.

No abstract

This is a review of human response to elevated levels of boron containing compounds with emphasis on studies containing sufficient detail for evaluation of dose‐response relationships. Qualitative information is also included where it will assist assessment of risk or contribute to clinical judgment. Skin absorption and dermatitis is also reviewed. Quantitative data are sparse, especially for infants and children. For acute oral doses in children, there are only two data points where dose and temporal relationships have been estimated with some care and where recovery was uneventful; these come from a single paper. Doses were 94.7 mg B/kg in a 24‐day infant and 30.4 mg B/kg in a 14‐month infant. Effects were irritability, mild diarrhea with vomiting, marked erythema in the diaper area at 94.7 mg, and sparse, mildly erythematous macular rashes on the face and neck at 30.4 mg. Adults given intravenous doses averaging 25 mg 10B/kg (range 19–46 mg 10B/kg) over a 75‐second period responded within 2 minutes with nausea followed by vomiting, excitation, and subsequent mild depression. No‐effect levels for humans can be established at about 1 g of boric acid per day (2.5 mg B/kg/day). The chronic adverse effect level is 5.0 mg B/kg/day. Infant response at high levels is similar enough to adult responses that it is reasonable to assume that the infant is not more sensitive than the human adult. Non‐systemic effects of boron are minor. Respiratory exposure in industry has not caused chronic pulmonary effects. Skin exposure does not cause dermatitis. © 1997 Wiley‐Liss, Inc.

No abstract

Developmental toxicity risk assessment has typically relied on the estimation of reference doses or reference concentrations based on the use of no-observed-adverse-effect levels (NOAELs) divided by uncertainty factors. The benchmark dose (BMD) approach has been proposed as an alternative basis for reference value calculations. In this analysis of the developmental toxicity observed in rats exposed to boric acid in their diet, BMD analyses have been conducted using two existing studies. By considering various end points (rib XIII effects, variations of the first lumbar rib, and fetal weight changes) and various modeling approaches for those end points, the best approach for incorporating all of the information available from those studies could be determined. Particular emphasis has been placed on methods for combining data across studies and for combining potentially related effects (on rib XIII and on the first lumbar rib). The issues of study and end point selection are ones that will arise frequently in the process of estimating reference values. This example of boric acid suggests that the BMD approach provides a reasonable basis for appropriately comparing and combining study data, as opposed to ad hoc combinations of study results. Moreover, it is shown that the BMD approach can be used with combinations of end points considered to differ in severity. In this case, the preferred approach involved combining the data from the two studies, which were similarly designed and were conducted in the same laboratory, to calculate BMDs that were more accurate and more precise than those that could be derived from either study alone. It was determined that decreased fetal body weight provided the best basis for BMD calculations; BMDs calculated for fetal body weight changes were less than those for all other relevant end points. The appropriate BMD to use as the basis for boric acid reference dose calculation appears to be 59 mg/kg/day, which is very similar to the NOAEL observed in the second of the two studies (55 mg/kg/day). Although the first study failed to establish a NOAEL, the BMD approach could have been applied to that study, thereby avoiding the need for a repeat study. Similar BMD results were obtained in both studies.