An overview of male reproductive studies of boron with an emphasis on studies of highly exposed Chinese workers.

Boron treatment of rats, mice, and dogs has been associated with testicular toxicity, characterized by inhibited spermiation at lower dose levels and a reduction in epididymal sperm count at higher dose levels. The no-adverse-effect level for reproductive effects in male rats is 17.5mg B/kg bw/day. Earlier studies in human workers and populations have not identified adverse effects of boron exposure on fertility, but outcome measures in these studies were relatively insensitive, based mainly on family size and did not include an evaluation of semen end points. A recent study of nearly 1000 men working in boron (B) mining or processing in Liaoning province in northeast China has been published in several Chinese and a few English language papers. This study included individual assessment of boron exposure, interview data on reproductive experience and semen analysis. Employed men living in the same community and in a remote community were used as controls. Boron workers (n=75) had a mean daily boron intake of 31.3mg B/day, and a subset of 16 of these men, employed at a plant where there was heavy boron contamination of the water supply, had an estimated mean daily boron intake of 125 mg B/day. Estimates of mean daily boron intake in local community and remote background controls were 4.25mg B/day and 1.40 mg/day, respectively. Reproductive outcomes in the wives of 945 boron workers were not significantly different from outcomes in the wives of 249 background control men after adjustment for potential confounders. There were no statistically significant differences in semen characteristics between exposure groups, including in the highly exposed subset, except that sperm Y:X ratio was reduced in boron workers. Within exposure groups the Y:X ratio did not correlate with the boron concentration in blood, semen and urine. In conclusion, while boron has been shown to adversely affect male reproduction in laboratory animals, there is no clear evidence of male reproductive effects attributable to boron in studies of highly exposed workers.

Chemesthetic responses to airborne mineral dusts: boric acid compared to alkaline materials.

OBJECTIVES: (1) To assess the relation between occupationally relevant exposures to dust of boric acid and magnitude of feel in the eye, nose, and throat during activity (pedaling) equal to light industrial work. (2) To compare feel from the dust of boric acid with that of the alkaline dusts calcium oxide and sodium tetraborate pentahydrate (sodium borate). (3) To chart how magnitude of feel changes with time in exposures up to 3/4 h. METHODS: Twelve subjects, six males and six females, participated in duplicate sessions of exposure to 2.5, 5, and 10 mg m(-3) of boric acid, 10 mg m(-3) of sodium borate, 2.5 mg m(-3) of calcium oxide presented as calcium oxide alone or diluted with hydrated calcium sulfate, and 0 mg m(-3) (blank). Exposures occurred in a plastic dome suspended over the head and closed around the neck with rubber dam. Measurements pre- and post-exposure included nasal secretion and nasal resistance. Measurements during exposure included rated magnitude of feel in the eye, nose, and throat, and respiration (Respitrace System). Six concentrations of carbon dioxide ranging from just below detectable to sharply stinging gave subjects references for their ratings. RESULTS: In general, feel increased for periods up to half an hour, then either declined or held at a plateau. Each material had a temporal signature. The nose led with the highest feel, followed by the throat, then the eyes. This hierarchy proved weakest for boric acid; at one level of exposure, magnitude in the throat overtook that in the nose. Accompanying measures implied that change of feel with time occurred neither because of an increase in dilution of the dissolved dusts in newly secreted mucus nor an increase of consequence in nasal resistance. Most likely, sensory adaptation determined the change. Boric acid of 10 mg m(-3) fell slightly and insignificantly below 10 mg m(-3) sodium borate in feel. Boric acid, though, showed a relatively flat dose-response relationship, i.e., a change in level caused little change in feel. CONCLUSIONS: The time-constant for feel from dusts lies on the order of tens of minutes. A flat concentration-response function for boric acid and a notable response from the throat suggests that perceived dryness, not mediated by acidity but perhaps by osmotic pressure, may account for the feel evoked at levels of exposure at or below 10 mg m(-3). More acidic dusts that could actually change nasal pH may trigger sensations differently.

Boron and the kidney.

Boron, the fifth element in the periodic table, is ubiquitous in nature. It is present in food and in surface and ocean waters, and is frequently used in industrial, cosmetic, and medical settings. Exposure to boron and related compounds has been recently implicated as a potential cause of chronic kidney disease in Southeast Asia. This observation prompted the present review of the published data on the effects of acute and chronic exposure to boron on renal function and structure in human beings and in experimental animals.

Sensory and associated reactions to mineral dusts: sodium borate, calcium oxide, and calcium sulfate.

Occupational exposure limits (OELs) for irritant dusts have had no quantifiable bases. This study (1) charted chemosensory feel, denoted chemesthesis here, to dusts of calcium oxide (1 to 5 mg/m(3)), sodium tetraborate pentahydrate [sodium borate] (5 to 40 mg/m(3)), and calcium sulfate (10 to 40 mg/m(3)); (2) examined correlates of the chemesthetic sensations; and (3) sought to illuminate the basis for potency. Twelve screened men exercised against a light load while they breathed air in a dome fed with controlled levels of dust for 20 min. Measured parameters included nasal resistance, nasal secretion, minute ventilation, heart rate, blood oxygenation, mucociliary transport time, and chemesthetic magnitude, calibrated to pungency of carbon dioxide. Subjects registered time-dependent feel from exposures principally in the nose, secondarily in the throat, and hardly in the eyes. Calcium oxide had the greatest potency, followed by sodium borate, with calcium sulfate a distant third. Of the physiological parameters, amount of secretion showed the best association with chemesthetic potency. That measure, as well as mucociliary transport time and minute ventilation, went into calculation of mass of dust dissolved into mucus. The calculations indicated that the two alkaline dusts increased in equal molar amounts with time. At equal molar concentrations, they had, to a first approximation, equal chemesthetic magnitude. On the basis of mass concentration in air or dissolved into mucus, calcium oxide and sodium borate differed in potency by a factor just above five, equal to the difference in their molecular weights. This relationship could inform the setting of OELs for a critical effect of irritation.