Much of the data on occupational exposure to cobalt have come from the tungsten carbide industry. McDermott , in 1971, found the average concentration of cobalt in 40 general air samples of seven tungsten carbide facilities to be below 0.1 mg/cu m (range, 0.005-0.15). About 70% of the 133 breathing zone samples were also less than 0.1 mg/cu m. Based on the data provided, however, mean concentrations in breathing zones of press operators and machine tool operators averaged 0.16 and 0.21 mg/cu m, respectively. A tungsten carbide facility reported that during 1977-78 the concentration of cobalt in worker breathing zones averaged 0.048 mg/cu m in the powder area, 0.033 mg/cu m in the pressing area, 0.019 mg/cu m in grinding, and 0.025 for general maintenance . The highest concentration measured was 0.17 mg/cu m and the lowest was 0.004 mg/cu m. A study of eight cemented carbide plants in Sweden revealed that exposure to cobalt varies considerably with job classification . Groups handling powder were most exposed, while press operators, shapers, dry grinders, wet grinders, face grinders, and inspection personnel received decreasing levels of exposure to cobalt (in that order). Some workers handling powder probably received short-term exposures in excess of 0.1 mg cobalt/cu m.# B ack grou nd R e s p i r a t o r y E f f e c t s E f f e c t s on t h e S k in C a r d ia c E f f e c t s E f f e c t s on B lo o d E f f e c t s on t h e T h y r o id C a r c i n o g e n i c i t y and M u t a g e n ic it y E f f e c t s on R e p r o d u c tio n O th er E f f e c t s D i s t r i b u t i o n and R e t e n t i o n EXTENT AND MEASUREMENT OF EXPOSURE

# Work C lo t h in g and P r o t e c t i v e E qu ip m en t The u s e and p r o p e r c l e a n i n g o f a p p r o p r ia t e w ork c l o t h i n g i s r e q u ir e d t o p r e v e n t s k i n e f f e c t s and s e n s i t i z a t i o n . P r o t e c t i v e e q u ip m e n t t h a t i s a p p r o p r ia t e t o t h e i r p o t e n t i

# S p ir o m e t r ic e x a m in a tio n t o d e t e c t r e s t r i c t i v e v e n t i l a t o r y im p a ir m e n t i s o n e p o s s i b i l i t y , b u t t h e r e s u l t s do n o t a g r e e t o t a l l y on t h e s e n s i t i v i t y o f t h i s t e s t . P e r h a p s much o f t h e c o n f l i c t i n g e v i d e n c e i s t h e r e s u l t o f t h e l e s s s o p h i s t i c a t e d eq u ip m e n t a v a i l a b l e t o t h e e a r l i e r i n v e s t i
A recent study at a Swedish hard metal plant attributed four cases of allergic alveolitis to exposure to soluble cobalt dissolved in the coolant used for wet grinding . One worker showed only signs and symptoms of asthma, but the other three showed evidence of mild pulmonary fibrosis as well.
All four had contact eczema and were sensitive to cobalt. Even though they ceased all exposure to cobalt, the four persons have continued to show abnormalities on their chest radiographs.

# (c) Other Reports of Respiratory Disease in Workers Exposed to Cobalt
Studies of the effects of cobalt exposure on workers not employed in the manufacture or use of hard metal are rare, but some indicate pulmonary disease in these workers.

# At a Finnish metal refinery, one or two new cases of bronchial asthma had been diagnosed annually in a group of 230-240 cobalt workers .
A cross-sectional study demonstrated a highly significant correlation between exposure to cobalt sulfate and asthma.
In contrast, nonasthmatic cobalt workers at the same plant had no evidence of any excess of chronic bronchitis. Kochetkova  described the death of a woman with a history of 7 years of exposure to metallic cobalt dust. The cause of death was cardiopulmonary insufficiency resulting from massive fibrosis. Levels of cobalt in the lung, liver, heart, id kidney tissue were described as markedly elevated. Her heart was enlarged, the liver and spleen were congested, and the cortical layer of the kidneys was swollen. In contrast, Cau et al  did not find radiographic evidence of fibrotic damage to the lungs of seven workers employed as sifters of cobalt powder. The workers had been exposed from 2 to 5 years, and they complained of cough, exertional dyspnea, nasopharyngeal irritation, and digestive disorders; two subjects had polycythemia. The authors concluded that exposure to finely divided cobalt metal dust did not induce pulmonary damage. In light of the toxic signs described by the workers and the short duration of exposure, this conclusion seems inappropriate.

# An extensive study of workers exposed to cobalt was reported by Verhamme
 in 1973. Medical examinations had been given to workers at a plant where cobalt oxides, powders, and salts were produced. Measurements of airborne cobalt were not reported, but the author believed that workers in the hydrometallurgic area had little or no dust exposure and that workers in the salts, oxides, and finished powders production areas were the most exposed groups. The finished powders had an average diameter of less than 1.4 jum, and To investigate the suggestion of Bruckner  that pulmonary reactions to cobalt may be mediated through a hypersensitivity mechanism, Kerfoot et al first exposed the experimental animals 6 hours a day for 5 days. After a 10-day lapse, the animals were reexposed 6 hours daily, 5 days a week for 3 months. All animals appeared normal until the 4th week of exposure, after which time the animals from both cobalt groups became lethargic.
Some animals appeared to be wheezing during exposure; this was confirmed by auscultation.
Postexposure pulmonary function tests showed a significant reduction in mean tidal volume, mean total compliance, and mean specific compliance in both cobalt-exposed groups . The authors interpreted change in compliance as demonstrating functional lung impairment. This change was reversed in animals examined 2 months after the cobalt exposure ended.
Serial radiographs conducted on all animals showed no evidence of diffuse pulmonary disease . The animals were examined grossly and by light microscopy at necropsy, and the lungs, heart, liver, and kidneys did not show any persistent or significant abnormalities. There was no evidence of cobalt in any lung tissue examined. Electron microscopic examination of lung biopsy tissue taken at the end of exposure revealed masses of collagen, elastic tissue, and fibroblasts in some of the tissues. However, no quantitative analysis was presented, nor was there mention of the methodology used in selecting tissue sites for examinations. The greatest changes were observed in the high-concentration cobalt exposure group, with the fewest changes being observed in controls.
In a Soviet study, male albino rats received exposures to aerosols of metallic cobalt continuously (24 hours a day, 7 days a week) for 3 months . There apparently was a concurrent control group, but the reports did not contain important details such as the number of animals exposed or tables of results presenting actual data.
Chronic inhalation of cobalt at 0.5 mg/cu m was said to be irritating to the lungs . The animals exposed to cobalt at 0.05 and 0.005 mg/cu m were described as having changes similar to, but less pronounced than, the changes in animals exposed at 0.5 mg/cu m. The lowest concentration (0.001 mg/cu m) produced what was described only as a weak general toxic effect.

# Microscopic examination of lung tissue from animals exposed at the highest concentration of 0.5 mg/cu m revealed accumulations of macrophages in the alveoli .
Interalveolar septa were consolidated in several areas of the lung. The severity of these changes reportedly was related to the exposure concentration.
The lungs of animals exposed at 0.001 mg/cu m were described as similar to those of controls. While information in this report is not completely satisfactory, effects such as consolidation of the alveolar septa are indicative of a prefibrotic condition.
Wehner et al  exposed 2-month-old Syrian golden hamsters to cobaltous oxide aerosols at 10 mg/cu m for their lifespans. The animals were exposed for 7 hours daily for 5 days a week to aerosols with a median diameter of 0.45 (an. Particulate material accumulated in alveolar macrophages and became denser as exposure continued. Emphysema became apparent. The extent of the changes became more severe as exposure time increased, and hyperplasia and hypertrophy of alveolar lining cells also appeared. Macrophages, frequently containing particulate matter, increased in number throughout the lung, and numerous focal accumulations of these cells could be found. Proliferative changes involving the epithelial components of bronchi and bronchioles became detectable early during exposure and increased in severity with exposure time.

# Laryngeal lesions occurred in five animals
(10%) during the study. The lifetime exposure of hamsters to cobaltous oxide clearly resulted in pneumoconiosis, but it did not significantly shorten their lives.
From the experimental studies in animals, the ability of some cobalt compounds to cause pulmonary fibrosis is evident. However, the information is insufficient to determine what effect, if any, exposure to other substances often present in cemented tungsten carbide may have on the development of hard metal disease. Thus, the possibility must be considered that adverse effects in workers exposed to cobalt at the 0.06-0.2 mg/cu m range were aggravated by exposure to mixtures.
However, the degree of worker exposure to cobalt is clearly related to the number of signs and symptoms observed in workers. Thus, decreasing exposure to cobalt should reduce the risk of adverse health effects. For cobalt metal, results in animals indicate that worker exposure should be limited as much as possible, and that in no case should the present Federal limit be exceeded. Similar information is not available for any other cobalt compound, including those in commercial use.

# Effects on the Skin
The incidence of sensitivity to cobalt in the general population appears to be low; in a small group ( 41 When all available data are combined, approximately 5% of the persons studied were cobalt-sensitive; 82% of these had combined metal sensitivities.
All three metals are prevalent in the general environment, which suggests that individuals with cobalt sensitivity also have had contact with nickel and chromium. Their responses thus could represent independent sensitization reactions, so that cross-sensitivity is not necessarily implied. The mechanism of the allergic response to cobalt after dermal contact is unknown. Haxthausen  contended that about 90% of the cobalt is absorbed from the skin following intradermal administration before any allergic reaction becomes visible. Norgaard , however, reported that cobalt is not absorbed through intact skin when applied to the forearm as a 0.3% or 5% solution. This same study reported systemic absorption of cobalt in solutions applied to the depilated skin of rabbits and guinea pigs . Another investigative group also observed systemic absorption when solutions of cobaltous chloride were placed on the clipped backs of guinea pigs . From this Information, NIOSH concludes that the risk of systemic poisoning from dermal absorption of soluble salts of cobalt is minimal for skin contact under normal working conditions. Abraded skin should be adequately protected to prevent contamination with cobalt compounds so that systemic absorption will not occur.

# Very few reports on skin diseases in workers who
No information is available to judge the effects of many cobalt compounds. Some organocobalt complexes are uncharged and relatively apolar, which would indicate that they probably can be absorbed dermally at least as effectively as the inorganic salts. At least some of these complexes may be stable compounds in body fluids, so that their toxic effects could differ from the simple salts. The authors considered the disease to be of occupational origin and attributable to cobalt. However, data to support this conclusion were not provided in the report.

# Cardiac Effects
Alexandersson and Atterhog  examined dry and wet grinders exposed to cobalt at 0.01 mg/cu m and powder handlers exposed at 0.06 mg/cu m.
No ECG changes were observed in dry grinders or powder handlers, even though the powder handlers showed evidence of impaired pulmonary function. The ECG's of wet grinders were abnormal and showed a high incidence of ectopic (premature) heartbeats. However, the authors believed that the ECG changes were related to exposure to cutting oils rather than cobalt.
Only one study in animals has examined the effects on the heart of cobalt exposure similar to that encountered in the workplace.
In the study on miniature swine exposed to cobalt metal dust at 0.1 or 1 mg/cu m, Kerfoot and coworkers  observed abnormalities in ECG's taken at the end of the 3-month exposure period.
These alterations were interpreted by the authors to indicate a decrease in the strength of ventricular contraction and repolarization abnormalities.
Sufficient evidence exists to suggest that both cobalt metal and cobalt salts can produce cardiac changes, but apparently only at high doses.
It should be noted that the amount of cobalt ingested daily by persons who consumed 6 liters a day of beer was about 5-10 mg, much higher than the amount inhaled by a worker breathing 10-15 cu m of air in a day at the current Federal limit of 0.1 mg/cu m. The question of whether changes such as those seen in the miniature swine could result in significant problems over a long period of exposure in especially susceptible individuals, such as those with existing heart disease and, possibly, persons who consume alcohol on a regular basis, needs to be examined.

# Effects on Blood
Cobalt-induced polycythemia is a well known effect. This property of cobalt has been exploited therapeutically in the treatment of refractory anemia .
The information collected for this review, however, revealed that other lesser known effects may occur at concentrations below those needed to produce polycythemia. The information available, although often incomplete, is presented below.

# The polycythemic effects of cobalt have been observed not only in patients but also in controlled experiments in persons with normal blood counts and in animals.
Volunteers receiving oral doses of cobaltous chloride ranging from 100 to 1,200 mg daily for 1-12 weeks  or 120-150 mg daily for 1-3 weeks  experienced an increase in RBC and Hb levels.
Numerous studies  in animals administered cobaltous chloride at high dosage levels for as long as 16 weeks either orally, or by subcutaneous (sc) or ip injection, also reported slight to substantial increases in RBC or Hb. One study in mice demonstrated an increase in RBC's subsequent to ip injection of cobaltous nitrate . However, inhalation studies in animals exposed to cobalt metal  provide little evidence to support the contention that polycythemia would be expected in workers exposed to cobalt at low concentrations. Similar studies on cobalt salts have not been conducted. Since the effects of cobalt on the blood would be expected to depend on its ability to concentrate at certain critical sites, cobalt salts might demonstrate effects at levels differing from cobalt metal. However, the mechanisms responsible for the changes in blood that are induced by cobalt are not known. The information available suggests to NIOSH that the effects of cobalt on the blood are multiple and poorly understood.

# While a polycythemic effect is clearly demonstrated in the reports
Polycythemia is clearly one manifestation of exposure to cobalt metal or cobalt salts, and increases in erythropoietin could be a factor in producing this effect.
The airborne concentrations of cobalt at which this polycythemic effect would be significant are poorly documented, but they appear to be well above the Federal standard for cobalt metal. Information is not adequate to judge whether this airborne concentration, 0.1 mg/cu m, would be adequate to prevent polycythemia from other cobalt compounds. Because RBC's have been found to decrease in exposed workers only at very high airborne concentrations of cobalt, this effect is judged insignificant if exposure is through inhalation. The role of cobalt in retarding blood clot formation is not well documented, but preliminary evidence suggests that it could be highly significant.

# Effects on the Thyroid
The Placebo tablets were substituted for the cobalt preparation, and thyroid function returned to normal by 12 weeks. Numerous additional reports that followed now show that 2-10 mg cobalt (as chloride)/kg given orally each day for 2-4 months will induce goiter formation in a small percentage of persons .
In all cases, the thyroid hyperplasi^ has been reduced or reversed after cobalt administration was stopped.
Controlled clinical studies have also examined the effects of cobalt on the thyroid gland. In one study, 12 adults with normal thyroids were given 50 mg of cobaltous chloride orally three times a day for 2 weeks .

# Radioactive iodine uptake was reduced in all but one person after the 1st
week; by 2 weeks all uptake levels were near zero. The effect was reversible after cobalt administration ceased. In a separate study, the majority of individuals given cobaltous chloride either orally or by iv infusion also had decreased iodine uptake in the thyroid . In fact, cobaltous chloride has been tested as a treatment for hyperthyroidism. Pimentel-Malaussena et al  observed that four of eight patients receiving 150-600 mg a day for up to 117 days responded with clinical improvement as manifested by reductions in tachycardia, metabolic rate, and uptake of radioactive iodine. Three of four, however, had thyroids of increased size, and the authors concluded that the action of cobalt was unpredictable. mg/cu m. This value is near the permissible exposure limit for cobalt metal fume and dust, and long-term effects at low levels have not been studied in humans for any cobalt compounds. This information suggests that alterations of thyroid function should be considered as a possible effect of workplace exposure to cobalt.

# The results of studies in guinea pi

# Carcinogenicity and Mutagenicity
Fibrosis, and not carcinogenicity, has received most of the attention of the occupational health community concerned with cobalt.
The many reports available concerning fibrosis would not be adequate to demonstrate any carcinogenic effect, because none are epidemiologic studies concerned with incidence rates. The three case reports describing the development of benign or malignant tumors in hard metal workers  and two epidemiologic studies describing an increased risk of lung cancer in cobalt recovery areas of nickel refineries  are not useful in demonstrating a possible carcinogenic effect of cobalt. Arsenic was also present in the air of some plants examined in the epidemiologic studies. Mixed exposures to substances known to be or suspected of carcinogenicity were involved in all cases. The case reports cannot distinguish between the role of occupational exposure and other factors, including normal incidence. Thus, information from human studies does not provide any answers about the possible carcinogenic potential of cobalt.
The two studies conducted in animals by routes of administration most applicable to workplace exposure did not demonstrate a carcinogenic effect for cobalt .
The incidence of tumor development was low and did not differ significantly from controls in male Syrian golden hamsters exposed for their life spans to aerosols of cobaltous oxide at 10 mg/cu m, 7 hours daily, 5 days a week . Many of these animals did develop fibrotic changes. Hamsters injected intratracheally once a week for 30 weeks with 4 mg of cobaltous cobaltic oxide (Co304) failed to develop a statistically significant excess of tumors compared with control animals . It should be noted, however, that the two tumors that developed in the 50 animals exposed to cobalt were alveolar in origin while the four tumors in controls were at sites unrelated to exposure.
These studies provide little evidence to suggest that cobalt oxides are carcinogens, but no similar studies have been conducted in animals other than hamsters.
The results of studies of the carcinogenic potential of cobaltous chloride are conflicting. Gunn et al  reported that no tumors were observed for 10-16 months in Wistar rats given four simultaneous injections of cobaltous chloride (0.18 mg cobalt/site) into a vital organ (liver or kidney), a gland (salivary or ventral prostate), and two mesenchymal mesodermal structures (chest, interscapular area, thigh, or femur).
Similarly, Shelley  reported that no tumors were observed in 10 ICR mice given cobaltous chloride (3.5 mg cobalt) in the dorsal earlobe, although the 2-to 5-month observation period was relatively short.
On the other hand, Shabaan et al  found subcutaneous fibrosarcomas in 14 of 27 rats surviving 8-12 months following 10 injections of cobaltous chloride at 40 mg/kg into the central abdominal wall. Two tumors were at the injection site, and the remainder were at various distances from the abdominal region. Metastases were not found in any tumorbearing animal. This study provides evidence that cobaltous chloride could be a carcinogen, and it argues for the need to perform chronic testing of cobalt salts in animals by routes of exposure more applicable to the workplace. Information on cobalt is inadequate to conclude that cobalt is a carcinogen. The information is also Inadequate to conclude that cobalt is noncarcinogenic.

# Several investigators have
In fact, limited data  provide suggestive evidence that at least some cobalt compounds may prove carcinogenic when subjected to long-term testing by currently accepted protocols. Until such testing is performed, no definitive guidelines can be given. Tumor induction at the injection site, however, would argue for the need to adequately clean any wound contaminated with cobalt.

# Effects on Reproduction
Whether exposure to a substance in the workplace can result in adverse effects on reproductive capacity or harm to the developing fetus is of grave concern to workers and to all persons responsible for the health of workers. The information available on cobalt is conflicting and insufficient to draw definite conclusions on the effects of cobalt on reproduction. Although this information dees not substantiate any effects, it is presented below.
Studies in humans  and animals   This experiment is of questionable relevance because of the nonmammalian test system used.
The literature describing the effects of cobalt on testicular function is characterized by disagreement among investigators. Hoey  reported marked but reversible changes (including suppression of spermatogenesis, abnormal sperm, deformation of the epididymal tubules, and necrosis of the duct system) in rats administered cobaltous chloride by sc injection. Kamboj and Kar  injected cobaltous nitrate sc in mice or intratesticularly in rats, and they found no microscopic damage to the testes or effects on spermatozoa. Niebroj  injected cobaltous chloride ip, and considered the effects on the testes of these mice to be generally positive.

# Other Effects
There are numerous studies of additional toxic effects attributed to cobalt. Some, such as the acute lethality studies in animals, have little impact on the occupational environment since such exposure conditions are rarely, if ever, encountered. Some effects, such as increased levels of plasma lipids, have been observed in humans, but only rarely in anemic patients receiving cobalt . Some, such as experimental induction of epilepsy by implantation of cobalt in the brain of animals, appear irrelevant. Other effects, such as kidney and liver changes, may be relevant; but information on occupational exposure is quite limited. also described its long-term accumulation in bone. Considering these sites of deposition, it is not at all surprising that a fraction of the administered dose is retained for a long time.

# Retention of cobalt oxides after inhalation has been examined in animals.
Wehner and Craig  reported that hamsters eliminated 90% of the total dose of cobaltous oxide, inhaled at 15.6 mg/cu m 7 hours a day for 2 days, within the subsequent 3 days (day 5 of experiment); however, the remainder was retained tenaciously in the body of the animal.
Barnes et al  administered respirable-sized particles of cobalt oxides by inhalation to dogs. In 10 days, only 10% of the cobaltous oxide was retained, compared with 60% of the cobaltous cobaltic oxide.
Cobaltous cobaltic oxide showed accumulation in the lymph nodes of the lung, a typical reaction of tissueinsoluble substances, while substantially more cobaltous oxide was found in the tissues and blood.
The information on distribution and retention of cobalt is typical of substances showing moderate to substantial tissue solubility. Information on the chloride salt is particularly revealing. It appears that enough of the salts can be absorbed through the gastrointestinal tract to warrant good sanitation and personal hygiene by workers so that they can avoid absorbing significant amounts of cobalt through ingestion. The long-term accumulation of cobalt in the liver may also be relevant.

# I I I . EXTENT AND MEASUREMENT OF EXPOSURE

# Uses of Cobalt
Cobalt (atomic number 27, atomic weight 58.93) Is a transition element located between iron and nickel in group VIII of the periodic table.
The metallic form is silver gray to bluish white and is magnetic. There are three oxides of cobalt: cobaltous oxide, CoO; cobaltic oxide, Co203; and cobaltous cobaltic oxide, Co304.
Ionic cobalt can exist in either a divalent or a trivalent form. The cobaltous ion can form numerous inorganic and organic salts , and cobalt can form complexes with amines, nitrites, and cyanides Cobalt alloyed with chromium and nickel is used in heat-resistant gas turbine blades and jet engine parts. Hard metal is found in high-speed cutting tools, armaments, masonry drills and cutters, high-speed dental drills, and tire studs. This property also leads to its somewhat unusual use as "invisible" ink. Cobalt pigments are very important in the ceramic and pottery industry.
A wide variety of pigments in differing shades and colors contain cobalt, often as mixtures with other metal salts. Black cobalt oxide paint is of particular value because of its heat and wear resistance. A mixture of cobalt oxide and cobalt aluminate forms a blue color. Cobalt blue is sometimes added to glass to detint the yellowish color that occurs if iron is present. Small amounts of cobalt salts are also used as boiler water scavengers, in magnetic tapes, and in steel-belted tires.

# Table III-l lists some occupations in which there is potential exposure to cobalt compounds .
The amount of exposure to cobalt that workers actually receive in these occupations probably varies widely. Large amounts of cobalt are used in some industries, such as cobalt salts manufacturing, the cemented carbide industry, and the manufacture of cobalt-containing alloys. Many users of these products handle extremely small quantities of cobalt. Others perform cutting, grinding, or welding operations on products, and the potential for worker exposure to cobalt is significant. Exposure of painters to cobalt driers is probably minimal; exposure of spray painters to cobalt pigments is not. Also, Janssens et al  reported that air samples collected in Belgium, apparently near a cobalt-manufacturing plant, showed levels of 0.4-7.3 ng/cu m (mean, 2.8). All of these levels in ambient air are far below the Federal standard of 0.1 mg/cu m for cobalt metal fume and dust.

# Environmental Data

# Cobalt is present in low concentrations

# TABLE I I I -l
At an operation where tungsten carbide tools containing 6 .0-8.5% cobalt were sharpened by wet grinding, general air samples were well below 0.1

# mg/cu m .
Two-thirds of the breathing zone samples, however, were above 0.1 mg/cu m of cobalt (range, 0.04-0.93 mg/cu m ) .
Full-shift TWA exposures were measured on a number of the grinders. Two-thirds of those values were above 0.1 mg/cu m with a range of 0.03-0.56 mg/cu m and a mean of 0.24 mg/cu m.
A US nickel refinery provided cobalt dust exposure data collected in June 1978 (B Roy, written communication, September 1978).
Average concentrations of cobalt were generally low, ranging from less than 0.002 to 0.099 mg/cu m, except for two tower cleanup workers whose exposures averaged 0.156 mg/cu m. Within the occupational groups, the concentration ranges were sometimes quite variable; for example, the exposure of one cobalt operator was 0.313 mg/cu m, and for a supervisor it was 0.148 mg/cu m, even though averages for all 13 workers in these groups were substantially lower. Where the dried cakes were broken into fine powders, cobalt concentrations varied, ranging from not detectable to 0.2 mg/cu m.
On the average, the drum-loading operations were the dustiest, but the cobalt concentrations, 0.04-0.5 mg/cu m, varied widely.
Other operations in the plant were contained and well ventilated so that the concentration of cobalt in those areas would be expected to be low. III-2 These data covered 1970 to 1974. Exposures to cobalt on the average were substantially less than 0.1 mg/cu m, but they were quite variable, even for the same areas. For example, exposure to cobalt in the breathing zones of workers in the melt shops were 0 .001-1.43 mg/cu m.

# An environmental survey conducted in May 1978 at a US jet aircraft engine assembly plant provided exposure data for three occupational groups (Table
In the powder products area, six samples ranged from 0.09 to 9.7 mg/cu m. General area samples tended to show a lower cobalt concentration than breathing zone samples.
Almost no published data on exposure to cobalt in welding and thermal cutting operations were found.
Hewitt  measured cobalt and other metallic contaminants in a number of welding operations in well ventilated areas. Airborne cobalt concentrations were all 0.1-0.4 jug/cu m.
Cobaltcontaining welding rods can contain other metals such as nickel or chromium that can also be hazardous if they become airborne.  Eight plant site visits were conducted to collect information for this report . The number of production workers ranged from less than 50 to 25,000.
The three largest plants (at least 800 production workers) all had formal plans for sampling and inhouse capabilities for analysis.
Two other plants sampled for cobalt on an irregular basis, and one other sampled for nuisance dust only. The two plants with less than 50 production workers had no program for air monitoring.
These plants had relied on corporate headquarters, insurance carriers, and contractors for air monitoring where in-house capability was unavailable.  One disadvantage of electrostatic precipitators is that actual worker exposure may not be estimated as closely as is possible with personal sampling.

# S am pling M ethods

# Analytical Methods
Many methods have been developed for the analysis of cobalt samples collected from air. Among these, colorimetric procedures can be satisfactory provided that other metals do not interfere with the results. Color reagents that have been used include nitroso R salt (sodium nitroso-2-naphthol-3,6disulfonate) and sodium thiocyanate . Although these methods are tedious and require skill, they can give satisfactory results.

# Emission spectrometric methods have been used frequently to analyze airborne particulate material.
Because of its sensitivity, the emission spectrograph has been used to measure pollutants in the community atmosphere , but this technique is also useful to determine concentrations of airborne cobalt in the workplace.
One investigator, using a specialized electrode for air sampling, was able to perform direct analysis of samples using the Although this method is sensitive and does not destroy the sample, the requirements for elaborate equipment, the safety precautions necessary for use of an irradiating beam or radioactive sources, and the relatively small thermal neutron cross section of cobalt make NAA less practical than AAS for routine use.

# Another technique for analysis of airborne cobalt use is the x-ray fluorescence method .
The fluorescence method resembles the neutron activation procedure in specificity, sensitivity, and ability to analyze a single sample for a number of elements. It is nondestructive and requires a minimum of sample handling. Results can be obtained quite rapidly for cobalt as well as for a number of other metals , and the x-ray fluorescence method can be an acceptable alternative to M S when analyzing cobalt.
In summary, the collection of air samples on membrane filters and the analysis of those samples by AAS, as described in the NIOSH P&CAM 173, are the methods of choice for monitoring of workers' exposure to cobalt (see the Appendix). Other methods, at least as sensitive and precise, are also acceptable.

# IV. CONTROL OF EXPOSURE
Over a million workers have some potential for exposure to at least one cobalt-containing compound in the course of their employment.
Many receive little exposure because they work with very small amounts of cobalt on an intermittent basis. Others, however, work with large amounts of cobalt regularly.
These workers can become exposed through inhalation, dermal contact, or ingestion. In some operations, exposure to cobalt is limited because of the use of extensive engineering controls. Other operations, however, require manual handling of materials containing cobalt.
Local exhaust ventilation  and good work practices can minimize exposure to cobalt in such circumstances. In all cases, ingestion of cobalt is easily prevented by the use of good personal hygiene in combination with the maintenance of a clean worksite. Workers who maintain or repair equipment, enter confined spaces such as tanks or vessels, or are involved in emergencies or other nonroutine situations have an especially high risk of exposure to cobalt.
These workers should be trained to recognize hazards, and in some circumstances they may require special protective equipment or clothing to decrease exposure.

# Information on typical industrial practices for the control of cobalt came from several site visits to plants manufacturing or using cobalt-containing products.
These plants included a refinery, an alloy producer, cemented tungsten carbide producers, and cobalt salt manufacturers.
Other sites visited included a welding-rod maker and an aircraft engine manufacturing facility. There is some published information on control of cobalt , but much of the following information came from plant visits .

# Engineering Controls
Well-maintained closed systems and the prevention of dust generation, when compatible with the operation involved, are the most effective methods of limiting worker exposure.
When a closed system is used, it must prevent or minimize the release of materials. When closed systems are not practical, worker exposure can often be reduced by process equipment modification, the use of control rooms, or local exhaust ventilation.

# Properly designed and maintained ventilation systems, including local exhaust systems, can prevent the accumulation of airborne cobalt-containing dusts and fumes. Local exhaust systems were in frequent use in the plants visited. Examples include the use of glove boxes for welding, exhaust hoods provided to individuals using hand-held buffers and grinders, local exhaust on the other grinding machines and on press machines, and dust-collecting hoses for packaging operations .
In addition, a ventilation system is desirable as a standby, should a closed system fail.
Where exhaust ventilation is required, adequate makeup air, conditioned as necessary for worker comfort, must be provided.
Ventilation requirements for grinding, buffing, and polishing operations were described in a NIOSH research report . Dry grinding equipment was classified as pedestal type, abrasive cutoff tools, surface-type disc grinders, portable grinders and cutoff machines, and other grinding machines according to ventilation system design requirements.
Polishing (coated abrasive) equipment was classified as wheel and drum type, disc type, belt polishers, and complex machines.
Buffing (loose abrasive) equipment was classified as pedestal type, portable, or multiple buffer machines.
For grinding and abrasive polishing, most of the equipment-generated particulate material was thought to be from the workplace. This would be so even for hard metal if a diamond wheel is used. Much more dust was contributed by the abrasive and the abrasive support materials in buffing. The report, in noting that the TLV for cobalt is very much less than for nuisance dust, considered that adequate control of cobalt is not likely to be possible with standard ventilation systems.
Totally enclosed ventilation systems and respiratory protection for personnel within the enclosure were recommended. However, many alloys containing only a small percentage of cobalt are used, and restrictions could be less severe in such cases. Engineering controls for most buffing and grinding machines are built to conform to the configuration of the equipment and the materials being handled. Specific guidelines, therefore, are difficult to propose. This can be exceedingly dusty, especially with fine powders.
Hoods that prevent the powder from dispersing into the work area and do not interfere with the weighing procedure are difficult, but not impossible, to design. Design requirements, however, are quite dependent on the size and shape of the container.
In most of the plants visited, engineering controls in use were generally not specific to cobalt alone, but rather to the entire process . For example, emissions from furnaces preparing specialty steels must be controlled for all the metals in the melt.
Cobalt may not be the limiting factor in control of exposure in such situations.
Ball mills used in the cemented carbide industry use solvents, such as acetone, and these emissions must be controlled. Several plants used cobalt in foundry operations where silica and other substances used in the molds dictated many of the control measures used. In milling, hot and cold rolling, and other operations, noise was often a factor in the use of control booths and of other means of control that often helped to lower exposure to cobalt. In buffing, exposure to the abrasive support material must be controlled as must oil mists generated in wet grinding.
In manufacture of salts, extensive use of strong acids led to requirements for emission control and cleanup procedures that also limited exposure to cobalt.
These overall requirements must be considered in designing engineering controls for cobalt.
To ensure effective operation of ventilation systems, trained personnel should conduct a regular monitoring program.
Routine inspection should include face velocity measurements of the collecting hood, examination of the air mover and collection or dispersion system, and measurements of atmospheric concentrations of cobalt in the work environment. Where appropriate, the use of continuous airflow indicators, such as water or oil manometers properly mounted at strategic locations and marked to indicate acceptable air flow, should be considered.
Any changes in the work operation, process, or equipment that may affect the ventilation system must be evaluated promptly to ensure that control measures adequately protect workers. All exhaust emissions from ventilation systems should be passed through a system designed to minimize the release or recirculation of raw materials, cobalt, and wastes into the occupational and community environments.

# Work Practices
Ultimately, any program of worker protection must consider the prevention of pulmonary fibrosis, which has been clearly demonstrated to result from excessive exposure to cobalt metal and oxides. Dermatitis and an occasional case of extreme pulmonary hypersensitivity to cobalt, however, are much more frequently encountered problems in the day-to-day operation of health care for cobalt workers.
These problems cannot be neglected in establishing an effective program for worker protection.
Employers should institute programs that emphasize good personal hygiene to prevent skin and respiratory irritation caused by cobalt-containing dusts. After working with cobalt products, workers should thoroughly wash their hands and face before drinking, eating, or smoking. If skin contact with cobalt solutions occurs, the worker should wash the affected skin promptly. The employer should provide showers if workers have substantial contact with cobalt.
These workers should be encouraged to wash or shower after each workshift. Employers should prohibit smoking or carrying of tobacco products in work areas because of possible cobalt contamination. For the same reason, employers should prohibit eating, food handling, or food storage within the work area.
To maintain a safe workplace, employers must identify the many physical hazards involved in handling cobalt and take measures to eliminate them.
In particular, several potentially hazardous situations were observed in plant site visits . These included sharp edges on some rolled alloys and rolled-alloy scraps, the need to lift heavy containers of cobalt, and press operators who placed their fingers under moving machinery to remove parts. Rolled alloy workers can avoid finger cuts by wearing gloves. Trained workers who follow proper lifting techniques could avoid back injuries when they lift dense material such as cobalt metal. Protective clothing must not increase the potential for injury of workers who handle cobalt when working with machinery with moving parts.
In storage, cleanup of spills, and emergencies involving fires, employers must be aware of the properties of individual cobalt compounds to ensure proper planning.
Finely divided cobalt will ignite, but its fire and explosion hazard is very weak [

# General plant maintenance must be conducted regularly to prevent cobaltcontaining dusts from accumulating in work areas.
Cleaning should be performed with vacuum pickup or wet mopping to minimize the amount of dust dispersed into the air.
A decontamination room should be available for cleaning equipment that is to receive major overhaul or maintenance. Spills of cobalt-containing material should be promptly cleaned up to minimize inhalation or dermal contact. Liquid material spills can be copiously flushed with water and channeled to a treatment system or holding tank for reclamation or proper disposal. Spills of dry material can be removed by vacuuming or wet mopping. Some spills can be removed by hosing, first with a mist of water to dampen the spilled material and then with a more forceful stream that flushes it into a holding tank or other facility for handling contaminated water. Work surfaces or contaminated clothing should never be cleaned by dry sweeping or blowing with pressurized hoses. Recovery systems used to reclaim waste metals should comply with Federal, state, and local regulations. All waste material generated in the handling of cobalt-containing substances should be disposed of in compliance with Federal, state, and local regulations.
Maintenance and repair workers face special problems regarding their potential exposure. The very circumstances that require the maintenance or repair work and dictate the work conditions will often preclude use of some control procedures. Consequently, very careful supervisory control must be exercised over such activities. These workers must wear appropriate protective equipment and clothing, and they must be trained to recognize and control the hazards they face. Special precautions are necessary when workers must enter tanks or vessels, such as reaction vessels containing cobalt catalysts or vessels used to prepare cobalt salts . Before any worker enters a vessel, all sources for transferring cobalt and other materials into or out ot the vessel must be blanked to prevent their entry. The vessel interior must then be washed with water and purged with air.
After purging the vessel's interior, trained personnel should test the vessel's atmosphere with suitable instruments to ensure that no hazards from fire, explosion, oxygen deficiency, or dust inhalation exist.
No one should enter a tank or vessel without first being equipped with an appropriate respirator and a secured lifeline or harness. Mechanical ventilation should be provided continuously when workers are inside the tank. At least one other worker similarly equipped with respiratory protection, lifeline, and harness should watch at all times from outside the vessel. Workers inside the tank must be able to communicate with those persons outside.
Other workers must be available to assist in an emergency. Flame-or spark-generating operations, such as welding or cutting, should be performed only when an authorized representative of the employer has signed a permit based on a finding that all necessary safety precautions have been taken. Gloves and protective sleeves should be used in manual transfer operations, together with a face shield (if respiratory protection is not needed) to keep soiled fingers from touching the face. Employers should provide change rooms and dual lockers so workers can remove soiled coveralls during breaks.

# Work Clothing and Protective
Work clothing should be worn for only a single day work period, then collected directly into a designated and labeled container, and laundered by a management-selected laundry service. This is encouraged to prevent the spread of contamination into the homes of workers. Eye irritation has apparently not been a problem for workers handling cobalt products; however, in operations that do scatter fine particles in the air, such as grinding, eye protection must be used that complies with 29 CFR 1910.133. Workers who are especially sensitive to cobalt or who handle solutions of cobalt in such a manner that cobalt can splash on the skin or into the eyes must wear protective suits, or face shields with goggles as appropriate, to prevent appreciable skin and eye contact. Emergency eyewashing facilities, where needed, must be readily available to affected workers.
Workers experiencing skin irritation should see a physician promptly.

# Respirators
are not a substitute for proper engineering controls. Respirators may be needed, however, for nonroutine maintenance work, entry into confined spaces, pending installation of adequate controls, and in emergencies where the concentration of cobalt could be unknown or excessive. In these situations, employers must provide workers with respirators, and establish a respiratory protective program meeting the requirements of 29 CFR 1910.134.
These programs should emphasize the importance of having clean, well-maintained, well-fitted respirators for use in unusual circumstances and emergencies. Workers must be aware of the need to guard against contamination of the interior of the facepiece. Table IV-

# Effective Planning
No program to minimize worker exposure to cobalt can be effective unless adequate attention has been given to problems before they arise. When a new facility is to be constructed, persons knowledgeable in occupational safety and health and industrial hygiene engineering should review plans both in the design phase and during construction. They should ensure that working areas and engineering controls are designed so that spills and airborne cobalt will be minimized when the plant is in operation.

# For plants already in operation, management should review materialhandling operations, maintenance and repair procedures, and process operations periodically.
This review should identify areas and job locations where workers might be exposed to cobalt or cobalt-containing waste products, either through inhalation or direct contact with the skin or eyes. If work practices or engineering controls in any area are no longer adequate, management should modify them promptly. Contingency planning for emergencies, inadvertent release of materials, and breakdown of facilities is vital. These plans should be developed for each department as well as plantwide. They should outline where appropriate equipment and trained personnel are located, and should be written, well understood by workers, and updated as required. Each plant should also be prepared to assess the impact or hazards of a specific spill or release of material should it reach a waterway or create a cloud. Supervisors should have information available, including lists of appropriate names and telephone numbers, for reporting emergencies.
In addition to internal reporting procedures, plant management should clearly understand what situations require recordkeeping or external reporting to OSHA, the Environmental Protection Agency (EPA), and any appropriate state agencies.

# Worker Education and Monitoring
A fundamental part of any program designed to provide a more healthful workplace involves education and monitoring of workers.
Workers who understand the reasons for rules concerning hygiene and work practices are more likely to help keep their work area clean.
For cobalt, medical and environmental monitoring are especially important since the potential effects of exposure are poorly understood.
Employers must follow the results of medical examinations and correlate them with exposure measurements to ensure that workers are adequately protected.
Workers should understand the importance of the medical and environmental monitoring to ensure that they will cooperate and report any possible adverse reaction to cobalt promptly. For workers in areas where the concentration of airborne cobalt is likely to exceed 0.05 mg cobalt/cu m (one-half the Federal limit), the employer should establish the following program.
Personal monitoring should be conducted to identify and measure, or permit calculation of, the exposure of each worker. Appropriate methods for sampling and analysis are listed in the Appendix.
2. Samples should be representative of the breathing zone air of workers, but source and area monitoring can be a useful supplement for identifying leaks or other sources of emissions.
While all workers do not have to be monitored, sufficient samples should be collected to characterize the exposure of all workers.
Variations in exposure during different shifts, because of location or job function and of changes in production schedule, should be considered in deciding the number of samples to be collected.
If a worker is exposed to cobalt at concentrations exceeding the Federal standard, improved measures to control exposure should be taken immediately.
Once the control measures are in effect, exposure monitoring should be repeated. If two consecutive measurements, taken at least 1 week apart, are below the Federal standard, the worker's exposure may be considered no longer excessive.
Personal monitoring records should be kept for 30 years to ensure compliance with new OSHA regulations concerning worker rights to information about their exposure (29 CFR 1910.20).
(c) Medical Surveillance N10SH encourages the provision of medical surveillance programs for workers. Some companies already maintain high-quality programs that allow absorption of hazardous chemicals to be detected at the earliest possible time.
This allows early intervention by surveying the workplace and initiating work practice and engineering changes necessary to protect workers.

# Medical
surveillance programs should ideally include preplacement examinations and periodic reevaluations that will, based on the characteristics of the individual substance or agent, allow detection of absorption before onset of perceptible damage.
In most programs, periodic examinations should be carried out on an annual basis. Since cobalt has been implicated to lesser or greater degrees with many effects on the body, these examinations should include not only the points discussed below but also be thorough enough to give reasonable assurance that effects have not occurred elsewhere in the body. The circumstances of each workplace and the types of cobalt compounds present will of course influence the program chosen by the responsible physician.
The most dramatic effect of cobalt is on the lungs, Involving development of pulmonary fibrosis. As a result, a medical history is important to determine the presence of factors that would argue against placement in a job requiring exposure to cobalt. The physical examination should give special attention to the chest and lungs. Because pulmonary function studies are sensitive indicators of early changes in lung tissues, NIOSH recommends that they be conducted yearly. The forced expiratory volume in 1 second (FEV 1) and forced vital capacity (FVC) tests are sensitive and easy to administer. Chest x-rays can be useful but are somewhat less able to detect early changes as compared to pulmonary function tests, so 3 years is probably a suitable time between radiologic examinations.
The skin should receive attention because cobalt compounds can cause allergic responses and sensitization. Once sensitized, a worker can probably not tolerate any additional exposure. As a result, any worker with a previous history of allergic skin disease should be carefully counselled and schooled in techniques that will minimize contact with cobalt. In addition, skin protection should be stressed in the workplace to keep the number of new cases of skin sensitization at a minimum.
Cobalt affects the thyroid gland, and results in production of goiter. While the strength of this association is not clear, it seems that palpation of the thyroid for enlargement would be a prudent and simple step to include. This standard is based on the TLV adopted by the AC6IH in 1968.  Workers in industries other than those manufacturing or using cemented carbide should be examined for adverse lung effects.

# V. BASIS FOR STANDARDS CONCERNING OCCUPATIONAL EXPOSURE TO COBALT
For both animals and humans, an attempt should be made to obtain dose-response data if fibrosis or prefibrotic changes are found.
The possibility that certain specialty steels cannot release cobalt in the lung following inhalation should be examined. Some of these substances are used because of their extreme heat and corrosion resistance. It is possible that their toxic effects are unrelated to their cobalt content.
An effort should be made to determine the prevalence of dermatitis caused by sensitization to cobalt in various US industries.
Information should be collected for different types of cobalt and should Include cobalt metal, cemented carbide, and cobalt salts. Work practices and types of protective clothing should be considered in order to determine the protection needed by workers to minimize their chances of becoming sensitized.
The issue of the possible carcinogenicity of cobalt is very much unresolved. Inhalation studies need to be conducted in animals, and such studies could be performed in conjunction with examination of possible fibrotic effects. In humans, epidemiologic studies should be conducted. The cemented carbide Industry, In particular, should be examined since the process is sufficiently old that an appropriate cohort should be available. Any epidemiologic study should also collect information on heart disease. The possibility that cobalt exposure at fairly low levels over a considerable period of time could lead to heart disease cannot be ruled out from information now available.
Finally, many cobalt compounds in commercial use have not been examined for toxicity, or very little information of limited use is reported.
For example, some cobalt pigments and cobalt driers for oil-based paints have widespread use. Compounds such as these should be subjected to thorough testing for toxicity. (f) V arious c l i p s , tu b in g , s p rin g co n n ecto rs, or b e l t s u f f i c i e n t to connect sampling apparatus to worker being sampled.

# C a l i b r a t i o n o f E quipm ent
Since th e accuracy of an a n a ly s is can be no g r e a te r than th e accuracy w ith which th e volume of a i r i s m easured, a c c u ra te c a l i b r a t i o n of th e sampling pump i s e s s e n t i a l .
The frequency of c a li b r a t io n re q u ire d depends on th e u se , c a re , and handling th a t the pump r e c e iv e s .
Pumps should be r e c a l i b r a t e d i f they have been abused or i f they have j u s t been re p a ire d or receiv ed from th e m anufacturer.
M aintenance and c a li b r a t io n should be performed on a r o u tin e sch ed u le, and re co rd s of th e se should be m aintained. (f) Check th e w ater manometer to ensure t h a t th e p re ssu re drop ac ro ss th e sampling t r a i n does not exceed 33 cm of w ater (approxim ately 2.54 cm of m ercu ry ). L ig h t-s c a tte r in g problems may be encountered when s o lu tio n s of high s a l t co n ten t a re being analyzed.
L ig h t-s c a tte r in g problems a re most sev ere when measurements a re made a t th e lower w avelengths, i e , below about 250 nm.
Background a b so rp tio n may a lso occur as th e r e s u l t of the form ation of v ario u s m olecular sp ec ie s th a t can absorb l i g h t .
The ( 1) 125-ml P h i l l i p s or G r i f f i n beakers w ith w atchglass covers.
(2) 15-ml graduated c e n tr ifu g e tubes.

# Reagents
(a) P u rity : ACS a n a l y t i c a l re ag en t grade chem icals or eq u iv a le n t should be used in a l l t e s t s .
R eferences to w ater s h a l l be understood to mean double d i s t i l l e d w ater or e q u iv a le n t. Care i n s e l e c t io n of re a g e n ts and in follow ing th e l i s t e d p re cau tio n s i s e s s e n t i a l i f low blank v alu es a r e to be o b tain ed .

# ( (d)
P e rc h lo ric a c id , re a g e n t grade.

# ml.
A sp ira te w ater a f t e r each sample.
As a minimum, a m idrange standard must be a s p ira te d w ith s u f f i c i e n t frequency, i e , once every f iv e sam ples, to ensure th e accuracy of th e sample d e te rm in a tio n s. I t i s b e s t to run a stan d ard w ith a c o n c e n tra tio n c lo se to th a t of a sample a f t e r each sample i s ru n .
To th e e x te n t p o s s ib le , base a l l d eterm in a tio n s on r e p l i c a t e an a ly se s.
Cobaltous n i t r a t e 8,600 Cobaltous o x a la te 1,700 Cobaltous s u l f a t e 8,300 C obalt cyanide 7,200 C obalt hydroxide 2,500 C obalt 2-eth y lh ex o ate 3,900 *Many of th ese workers would be p o t e n t i a l l y exposed to only sm all amounts of c o b a lt through i n h a la tio n , in g e s tio n , o r dermal c o n ta c t.
The exposure e stim a te s are not a d d itiv e , sin ce some workers would be exposed to more than one compound. Substance(s) com prising the d r i e r were no t i d e n t i f i e d .
Thyroid function studies do not seem necessary unless enlargement or some other sign or symptom of thyroid dysfunction la present.
Present information suggests the possibility of polycythemia in the blood and electrocardiographic changes in the heart being produced by exposure to cobalt. The information is very unclear and appears to show effects only at a very high dosage. Therefore, no specific tests are suggested for these organ systems unless there is a potential for exposute to high levels of cobalt in the workplace.
The medical surveillance program should be reevaluated frequently and changed to reflect current working conditions and knowledge of health effects. Medical records should be kept for 30 years after the worker's last exposure to cobalt. This will ensure compliance with OSHA's (29 CFR 1910.20) standard concerning worker's rights to his or her own medical records.

# V I I . REFERENCES
Morral FR: Cobalt and cobalt alloys, in Standen A (ed.): Kirk-Othmer Encyclopedia of Chemical Technology, ed 2 rev. New York, Interscience Publishers, 1970, vol 5, pp 716-48 2.
Hawley GG (ed.):
The Condensed Chemical Dictionary, ed 9. New York, Van Nostrand Reinhold Co, 1977, pp    The effects of cobalt injections on total circulating red cell volume and bone marrow cytology in normal and adrenalectomized dogs.      , 1970, pp 197,210,223,231,278,287,303,343,347  Once th e ashing i s com plete, remove th e w atch g lass, and allow th e sample to evaporate to near dryness (approxim ately 0 .5 m l). I f c h a rrin g o c c u rs, add HN03 (1 ml) and evaporate to near dryness (0 .5 ml) again.
R epeat, i f n ecessary .
Remove th e beaker from th e h o t p la t e , c o o l, and add 1 ml HN03 and 2-3 ml of d i s t i l l e d w ater.
T ra n sfer th e s o lu tio n q u a n t i t a t i v e l y w ith d i s t i l l e d w ater to a 10-ml volum etric f l a s k , and then d i l u t e th e samples to volume (10 ml) w ith w ater.