No studies were located regarding cardiovascular, gastrointestinal, hematological, musculoskeletal, or renal effects in humans after inhalation exposure to boron. No studies were located regarding dermal/ocular effects after acute inhalation exposure in humans or animals for any duration category.
Information on respiratory, cardiovascular, gastrointestinal, hematological, musculoskeletal, renal, and dermal/ocular effects is discussed below. The highest NOAEL values and all reliable LOAEL values for these systemic effects for each species and duration category are recorded in Table 2-1 and plotted in Figure 2-1.
Respiratory Effects. Boron (as boron oxide and boric acid dusts) has been shown to cause irritation of the upper respiratory tract in humans. Based on a medical questionnaire from 113 workers (96% males, 4% females) employed in the borax industry for an average of 11 years, mean exposures of 4.1 mg/m to boron oxide and boric acid dusts were associated with dryness of the mouth, nose, or throat, sore throat, and productive cough (Garabrant et al. 1984). While the authors reported differences between the test and control groups in age and numbers of smokers, no differences in symptoms were observed. Similarly, symptoms of acute respiratory irritation were related to exposures to borax dust at concentrations of 4 mg/m or more in a cross- sectional study of 629 borax workers actively employed for 11.4 years (Garabrant et al. 1985). Decreases in the forced expiratory volume (FEV1) were seen among smokers who had cumulative borax exposures of 80 mg/m or greater but were not seen among less exposed smokers or among nonsmokers. Radiographic abnormalities were not found. It was determined in a follow-up of the Garabrant et al. 1985 study that the cumulative borax exposure effect found previously was probably due to smoking workers with longer boron work histories and who smoke disproportionately more than those with shorter work histories. There was no indication that borax exposure at the levels studied (up to 15 mg/m ) impaired pulmonary function (Wegman et al. 1991). Direct irritation to mucous membranes of the nose and throat was also studied by Wegman et al. (1991) using an irritation scoring system together with real-time measurements of borax exposure concentrations. The study concluded that borates are mild irritants. However, these effects are likely to occur at concentrations exceeding 10 mg/m (OSHA Permissible Exposure Limit).
TABLE 2-1. Levels of Significant Exposure to Boron and Compounds - Inhalation
Key to Species frequency/ NOAEL Less serious Serious figure* duration System (mg/m3) (mg/m3) (mg/m3) Reference Form
INTERMEDIATE EXPOSURE Systemi c 1 Rat
Reproducti ve 4 Rat
470 (respiratory i rri tati on)
Wi1gi ng et al. 1959
Wi1di ng et al. 1959
Wi1di ng et al. 1959
Wi1di ng et al. 1959
CHRONIC EXPOSURE Systemi c
Derm/oc i rri tati on) 4.1 (respiratory i rri tati on) 4.1 (eye irritation)
et al. 1985 Garabrant et al. 1984
BX BA BO
aThe number corresponds to entries in Figure 2-1.
BA = boric acid; BO = boron oxide; BX = borax; Cardio = cardiovascular; d = day(s); Derm/oc = dermal/ocular;
Gastro = gastrointestinal; Hemato = hematological; hr = hour(s); LOAEL = lowest-observed-adverse-effect level; Musc/skel = musculoskeletal; NOAEL = no-observed-adverse-effect level; Resp = respiratory; wk = week(s); yr = year(s)
Animal studies suggest that the respiratory tract is susceptible to boron toxicity. Rats exposed to 470 mg/m boron oxide aerosol for 10 weeks developed reddish exudates from their noses, but there were no deaths or signs of lung damage (Wilding et al. 1959). No changes were observed in rats in the 77 mg/m dose group after 24 weeks of exposure, or in dogs exposed to a concentration of 57 mg/m3 for 23 weeks (Wilding et al. 1959).
Cardiovascular Effects. Animal data are sparse. Rats exposed to aerosols of boron oxide at a concentration of 77 mg/m for 6 weeks showed no histopathological effects in the cardiovascular system (Wilding et al. 1959).
Gastrointestinal Effects. Animal data are sparse. No changes were seen in the gastrointestinal tract of rats exposed to aerosols of boron oxide at a concentration of 77 mg/m for 6 weeks (Wilding et al. 1959).
Hematological Effects. Little is known concerning the effects of boron in animals. Rats exposed to aerosols of boron oxide for 10-24 weeks (up to 470 mg/m ) and dogs for 23 weeks (57 mg/m )showed no significant changes in total red and white blood cell count, hemoglobin, hematocrit, and differential count (Wilding et al. 1959).
Musculoskeletal Effects. Animal data are sparse. No histopathological effects of exposure were observed in the femur, rib, and muscle of rats exposed to aerosols of boron oxide at a concentration of 77 mg/m for 6 weeks (Wilding et al. 1959).
Renal Effects. Data on the effects of boron in animals are sparse. No renal effects were observed in rats exposed to aerosols of boron oxide at a concentration of 77 mg/m for 6 weeks (Wilding et al. 1959).
Dermal/Ocular Effects. Human occupational exposure to a mean concentration of 4.1 mg/m (as boron oxide and boric acid dust) produced eye irritation following chronic exposures in workers employed for an average of 11 years (Garabrant et al. 1984, 1985).
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