j.10MMT combustion products

j.10MMT combustion products

The chronic inhalation toxicity of Mn oxide (Mn₃O₄) as a combustion product of MMT was the subject of a report (Rinehart, 1975) published subsequently by Ulrich et al. (1979 a,b,c).

Ulrich et al. (1979a) documented the experimental procedure to examine the chronic inhalation toxicity of MMT combustion products. MMT combustion products, ‘similar to that produced by an internal combustion engine’, were generated by burning MMT vapours in a propane flame. This method was reported to produce a particulate matter consisting of Mn oxide (Mn₃O₄) with an aerodynamic diameter of approximately 0.11μm.

Using the experimental procedure published by Ulrich et al. (1979a), monkeys and rats were exposed to Mn oxide (Mn₃O₄) aerosol produced by the combustion of MMT. The animals were exposed for 24 hours per day for nine months to 0, 11.6, 112.5 or 1152 g Mn/m³ as Mn oxide (Mn₃O₄) aerosol. Each treatment group contained 15 male and 15 female rats and 4 male and 4 female monkeys. No clinical signs of toxicity were observed at the end of the exposure period. Weight gain was normal in all monkeys, while rats exposed to 1152 g Mn/m³ as Mn oxide exhibited an accelerated weight gain. Monkeys in the highest dose group had increased levels of haemoglobin, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration. The mean corpuscular haemoglobin level was also increased at 112.5 g Mn/m³ as Mn oxide. At the highest dose, rats exhibited increased haemoglobin, erythrocytes, mean corpuscular haemoglobin concentration and a decrease in mean corpuscular volume. At the same dosage male rats also showed increased mean corpuscular haemoglobin. At 112.5 g Mn/m³ as Mn oxide, male rats showed decreased reticulocytes and leukocytosis, while females exhibited decreases in hematocrit, haemoglobin, mean corpuscular haemoglobin and mean corpuscular volume. The authors state that while the effects were statistically significant, they may be within an acceptable normal range. All effects were reversible, as demonstrated by normal values at 6-months post exposure. Clinical chemistry evaluations revealed that at 1152 g Mn/m³ as Mn oxide male rats were found to have a depressed serum phosphate level. Microscopic evaluations revealed that brain, sternal bone marrow, and lung tissue were free of any changes. A small increase in liver weight was observed in female rats at 1152 g Mn/m³ as Mn oxide. The weight of other major organs was considered normal (Ulrich et al., 1979b).

In a follow-up publication by Ulrich et al. (1979c), the effect of MMT combustion products on pulmonary function was reported in each treatment group containing 15 male and female rats and 4 male and female monkeys. With regard to pulmonary function, there was a significant but small increase in tidal volume in male monkeys that received 112.5 g Mn/m³ as Mn oxide. Apart from this effect pulmonary function was considered normal. Although 14/112 electromyographic and limb tremor oscillograph records demonstrated possible abnormalities, the abnormal findings were evenly distributed between the dosage groups suggesting there were no exposure related effects (Ulrich et al., 1979c).

The toxicity of MMT combustion products was also tested via exposure of 180 male golden hamsters and 370 male outbred albino rats to automotive emissions generated using a 1972 Chevrolet 350 CID engine dynamometer system. Emissions were derived by passing exhaust generated from the combustion of fuel consisting of indolene “clear” containing MMT at 0.25 g Mn/gallon through a muffler, followed by dilution (25:1) with clean conditioned air. The final diluted emissions were split in two with one half being irradiated prior to exposure to animals. Irradiated emission typically contained 855 g/m³ particles (0.29 m) consisting of 117 mg/m³ Mn (13.7%). Nonirradiated emission typically contained 635 g/m³ particles (0.26 m) consisting of 131 mg/m³ Mn (20.7%). Animals were exposed for 8 hours per day for 56 consecutive days. Animals were sacrificed and tissues were collected for histological evaluation and Mn analysis. Alterations in general condition, appearance and weight gain were not observed. Hamsters were deemed to be free of abnormalities at necropsy while chronic respiratory disease lesions were observed in rats. Lesions observed in the lung consisted of a thickened, cuboidal epithelium at the terminal bronchiole that extended partly down the respiratory tree. These changes were noted in 21%, 14%, and 6% of irradiated, nonirradiated and control animals respectively. The degree of severity of the lesions did not appear to increase with exposure duration. A chronic hepatitis around portal triads was also observed. Manganese levels in the tissues (brain, liver and lung) of exposed animals were generally higher than controls (Moore et al., 1975b).

j.11Human exposure

Ethyl Corporation reported an incident of acute exposure to MMT. Three workers were reportedly exposed to an unknown concentration of airborne MMT for a short period and two workers were sprayed with the material. Symptoms reported included burning of the skin, a metallic taste in the mouth, headache, nausea and chest tightness. These effects abated within 24-48 hours.

Four workers were reportedly exposed to MMT in an 18 x 20 foot room when approximately 25 gallons (half a drum) of neat MMT was poured into a large open steam-heated pot. The MMT was heated long enough to form vapours as the workers detected an unusual odour within 5 minutes, when they shut off the heat and left the building. The four workers were examined immediately and no adverse effects or symptoms were noted. No symptoms were also reported 24 hours post exposure. Three hours post exposure the urine of the four workers contained 23, 87, 20, and 10 g Mn/L. Twenty three hours post exposure urine levels had dropped to 8, 22, 5, and 10 g Mn/L and workers were still free of symptoms.

Six individuals who reportedly experienced a 30 min skin exposure to MMT all reported a burning sensation of the skin and metallic taste in the mouth. Other symptoms included headache (4/6), nausea (4/6), gastrointestinal upset (3/6), dyspnea (3/6), chest tightness (1/6) and paresthesia (1/6). All symptoms appeared within 5-60 min post exposure and had abated in four individuals within 2-4 hours. The remaining two individuals reported that abdominal distress lasted for 2 days.

In 1959, two men wearing rubber gloves and air masks were exposed to a fine spray of neat MMT caused by a leak during a pumping operation. Although the hands and face of the two workers were covered, the spray moistened the remainder of both workers bodies for approximately 1.5 hours. The socks and shoes of both workers were saturated. On examination, the two men complained of a slight burning of the skin. Blood parameters and muscular co-ordination were unaffected. On the day of the exposure, urine Mn levels of the two workers were 137 and 46 g/L. Several weeks later urine Mn levels were 3.4 and 2.9 g/L.

A small volume of MMT, reportedly 5-15 mL when spilt on the wrist of a worker caused “thick tongue”, giddiness, nausea and headache within five minutes (U.S. Navy, 1968).