Evaluation of sensory irritation of delta3-carene and turpentine, and acceptable levels of monoterpenes in occupational and indoor environment

The standard mouse bioassay was used for obtaining the RD50 (i.e., the concentration that causes a 50% decrease in respiratory frequency) and for estimating the irritation properties of d-delta3-carene (i.e., (+)-delta3-carene) and commercial turpentine. The chemicals studied possess mainly sensory irritation properties similar to the previously studied monoterpenes, pinenes. The irritation potency of d-delta3-carene (RD50 = 1345 ppm) was almost equal to that of d-pinenes. Thus, d-delta3-carene was about four times more potent as a sensory irritant than I-beta-pinene, whereas the difference with I-alpha-pinene was more marked; as a sensory irritant, I-alpha-pinene is almost inactive. Based on sensory irritation potency and physicochemical and structural properties of pinenes and delta3-carene, the potency of a closely related monoterpene, limonene, is discussed. For commercial turpentine, a mixture of monoterpenes (mainly d-delta3-carene, I-beta-pinene, alpha-pinenes, and limonenes), the RD50 (1173 ppm) was the same order of magnitude as those of d-pinenes and d-delta3-carene. Apparently, d-monoterpenes are responsible for the sensory irritation caused by turpentine. In the wood industry and in the indoor air of nonindustrial environments, monoterpenes are thought to be one of the causative agents for irritation symptoms. The occupational exposure limit (OEL) of turpentine (100 ppm in Finland and the United States) is also used for individual monoterpenes, excluding limonene. Using results from this and our previous study, proposed OELs and recommended indoor levels (RILs) for selected monoterpenes and turpentine were determined based on their RD50 values. According to our studies, the present OEL of turpentine (100 ppm; 560 mg/m3) in Finland and in the United States seems to be suitable only for I-pinenes. For d-monoterpenes and turpentine, an OEL about three times lower is suggested. Our results show that recommended indoor levels (RILs) for monoterpenes are high compared to the concentrations measured indoors in nonindustrial environments. Thus, it is very unlikely that monoterpenes alone can cause irritation symptoms in homes or offices under normal conditions.

Gas chromatographic determination of some alkoxysilanes for use in occupational exposure assessment

The manufacture and application of organosilicon compounds, especially silanes, have increased dramatically during recent decades. This has led to an increase in the number of exposed workers in different areas of industry. Therefore, there is an urgent need for an analytical method which can assess exposure to these compounds. A capillary column gas chromatographic (GC) method was developed for detecting 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane. The silanes diluted in heptane were analysed by GC using flame ionisation detection. Gas chromatography-mass spectrometry was used to confirm the identity of the GC peaks. The analytical range of the method varied from 1 or 5 micrograms ml-1 to 500 micrograms ml-1 depending on the silane being studied. The detection limits were 1 microgram ml-1 for 3-methacryloxypropyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane and 5 micrograms ml-1 for 3-aminopropyltriethoxysilane. The mean recovery of silanes tested with patch samples was > 95% for all of the silanes. The repeatability of the patch sample method for silanes varied from 6.5 to 10.1%. This new GC method allows the simultaneous determination of three organosilicon compounds for occupational exposure assessment.

Exposure to airborne microorganisms and volatile organic compounds in different types of waste handling

Occupational exposure of workers to airborne microorganisms and volatile organic compounds (VOC) in different types of waste treatment situations was examined during summer time. Microorganisms were collected as stationary samples using a six-stage Andersen impactor, while for VOCs both personal and stationary sampling was conducted. The exposure at the waste handling facility was considerably greater than at landfill sites or in waste collection. The concentrations of viable fungi were maximally 10(5) cfu/m3, and the concentrations of both total culturable bacteria and Gram-negative bacteria exceeded the proposed occupational exposure limit values (OELV), being 10(4) and 10(3) cfu/m3, respectively. Exposure to VOCs in the waste handling facility was three times higher than at the landfill sites, being at highest 3000 microg/m3, considered to be the limit for discomfort. The use of personal protective equipment at work, thorough hand washing and changing clothes after the work shift are strongly recommended in the waste handling facility and the landfill sites.

Qualitative identification of volatile metabolites from two fungi and three bacteria species cultivated on two media

Two fungal species, Aspergillus fumigatus and Penicillium brevicompactum and three bacteria, Klebsiella pneumoniae, Enterobacter agglomerans and Streptomyces albus were cultivated on two media, malt extract agar and dichloran glycerol agar. The volatile metabolite samples from the cultures were adsorbed on Tenax TA and analyzed qualitatively by thermal desorption gas chromatography and with a mass selective detector. Various hydrocarbons, alcohols, ketones, esters and terpenes were identified. The production was highly dependent on both the medium and the microbial species. 2-Methyl-1-propanol, 2-methyl-1-butanol and 3-methyl-1-butanol were the most commonly produced substances. The bacterial species did not produce any hydrocarbons that were characteristic to the fungi (e.g. methyl-1,3-pentadiene, 1-octene and 1,3-octadiene or 8-carbon alcohols 1-octen-3-ol and 3-octanol). Instead, K. pneumoniae and E. agglomerans produced 3-hydroxy-2-butanone and 1-hydroxy-2-propanone, which were not produced by the fungi. Geosmin and a large number of sesquiterpenes were produced by S. albus.

Stereospecificity of the sensory irritation receptor for nonreactive chemicals illustrated by pinene enantiomers

To clarify the existence of a receptor protein for sensory irritants in trigeminal nerve endings, D- [i.e. (+)] and L- [i.e. (-)] enantiomers of alpha- and beta-pinene as models of nonreactive chemicals were evaluated for their potency in outbred OF1 and NIH/S mice using ASTM E981-84 bioassay. All pinenes possess sensory irritation properties and also induced sedation and signs of anaesthesia but had no pulmonary irritation effects. According to the ratio of RD50 (i.e. concentration which causes a 50% decrease in respiratory rate,f) and vapour pressure (Po), all pinenes are nonreactive chemicals. For nonreactive chemicals, Po and olive oil-gas partition (Loil) can be used to estimate their potency as sensory irritant. Thus, for enantiomers with identical physicochemical properties, the estimated RD50 values are the same. In addition, although alpha- and beta-pinene do not have identical Po and Loil values, their estimated potencies are quite close. However, the experimental results showed that D-enantiomers of pinenes were the most potent as sensory irritants and a difference in potency also exists between alpha- and beta-pinene. RD50 for D-enantiomers of alpha- and beta-pinene were almost equal, 1053 ppm and 1279 ppm in OF1 strain and 1107 ppm and 1419 ppm in NIH/S strain, respectively. Values differed by a factor of approximately 4 to 5 from L-beta-pinene for which the RD50 was 4663 ppm in OF1 and 5811 ppm in NIH/S mice. RD50 could not be determined for L-alpha-pinene; this pinene was almost inactive. D-alpha-pinene seems to best fit the receptor because its experimental RD50 was one-half of the estimated value while for D-beta-pinene those values were equal. On the contrary, L-beta-pinene was about 3 to 4 times less potent than estimated. L-alpha-pinene was only slightly active although it was estimated to be as potent as D-alpha-pinene. The remarkable difference in potency between L-enantiometers is most likely due to a structural difference between alpha- and beta-pinene: the more flexible beta-pinene can bend to fit into the receptor better than the rigid alpha-pinene. The results showed that the commonly used physicochemical descriptors cannot fully explain the potency of these chemicals; their three-dimensional structure should also be considered. Because of the stereospecificity of pinenes, a target site for nonreactive sensory irritants is most likely a receptor protein containing a chiral lipophilic pocket.

Urinary NAG and GAG as biomarkers of renal effects in exposure to 2-alkoxyalcohols and their acetates

Many sensitive biomarkers are available for the surveillance of the early health effects of chemicals on humans. This study was conducted to evaluate the usefulness of glycosaminoglycans (GAG) as biomarkers of early kidney effects in exposure to 2-alkoxyethanols and their acetates. GAG were compared with effects on the urinary beta-N-acetylglycosaminidase activity (NAG). According to the results of the present study, the excretion rate of GAG was higher among women than men. On the other hand, the excretion rate of GAG was lower among exposed subjects than among the controls, and the level was decreased at the tested levels of exposure. The NAG activity was higher in most of the exposed groups than in the controls. The data indicated that an appropriate urinary limit value for ethoxyacetic acid was 30 mmol/mol creatinine in postshift samples and that this value corresponded to an 8-hour exposure level of 2 cm3/m3 2-ethoxyethylacetate. Urinary butoxyacetic acid excretion of 60 mmol/mol creatinine corresponded to the inhalation exposure level of 5 cm3/m3 2-butoxyethanol and its acetate in postshift samples.

Biological monitoring of occupational exposure to 1-methoxy-2-propanol

At the end of a workweek 23 silkscreen printers gave a urine sample for capillary gas chromatographic analysis for 1,2-propanediol. The mean concentration was 2.52 (S.D. 2.01) mmol mol creatinine(-1) (median=1.76, n=23). The urinary excretion of 1,2-propanediol was linearly dependent on the preceding 1-methoxy-2-propanol exposure measured in the worker's breathing zone [y=0.99+0.28x, n=23, r=0.67, where y is the urinary 1,2-propanediol concentration, in mmol mol creatinine(-1) and x is the concentration, in cm3 m(-3), of 1-methoxy-2-propanol (90.2%), 1-ethoxy-2-propyl acetate (5.8%), 1-methoxy-2-propyl acetate (2.1%) and 1-ethoxy-2-propanol (1.9%) in the air].

Urinary alkoxyacetic acids and renal effects of exposure to ethylene glycol ethers

OBJECTIVES

Ethylene glycol ethers and their acetates are widely used in industry, because of their hydrophilic and simultaneously lipophilic properties. Ethylene glycol ethers and their acetates are mainly metabolised to alkoxyacetic acids, but there is also a minor pathway through ethylene glycol to oxalic acid. The main pathway of ethylene glycol ethers is associated with significant clinical or experimental health effects and the minor pathway is also interesting because formation of urinary stones depends principally upon the urinary concentration of oxalate and calcium.

METHODS

Excretion of alkoxyacetic and oxalic acids was examined among silkscreen printers for an entire working week. The aim of the study was to evaluate alkoxyacetic acids as early indicators of exposure to glycol ethers and to evaluate their toxicity to kidneys. The load of alkoxyacetic and oxalic acids was compared with the excretion of calcium, chloride, ammonia, and glycosaminoglycans (GAG). Morning urine was chosen for the main analysis, as the overall metabolite, ethoxyacetic acid (EAA), has a long elimination time from the body.

RESULTS

The excretion of calcium increased according to the urinary alkoxyacetic acid load. The excretion of ammonia and chloride was higher among the exposed workers than among the controls. The highest urinary alkoxyacetic acid load was also associated with increased excretion of GAG, which may reflect the toxicity of metabolites of ethylene glycol ether. The excretion of GAG correlated positively with that of calcium in the printers with highest exposure. The tendency to form urinary stones was 2.4-fold higher among silkscreen printers than among office workers.

CONCLUSION

On the basis of renal effects our study indicates the need for establishing a new biological exposure limit before a workshift that is clearly below 100 mmol ethoxyacetic acids per mol creatinine in morning urine of people occupationally exposed to ethylene glycol ethers.

Determination of urinary 2-mercaptobenzothiazole (2-MBT), the main metabolite of 2-(thiocyanomethylthio)benzothiazole (TCMTB) in humans and rats

A method for biological monitoring of urinary 2-(thiocyanomethylthio)benzothiazole (TCMTB), a wood preservative and an industrial chemical, was developed. Three different doses of TCMTB in olive oil were given to male rats by gavage for 3 weeks. Urine was collected daily and the metabolites were analysed as thioethers by derivatization with pentafluorobenzyl-bromide by gas chromatography-mass spectrometry. The parent chemical was not detected in urine samples, but two metabolites of TCMTB were identified. 2-Mercaptobenzothiazole (2-MBT) was the main metabolite, and its excretion varied according to the dose. The second metabolite was 2-(mercaptomethylthio)benzothiazole. The amount of 2-MBT excreted in rat urine was 66 +/- 12% (SD), 51 +/- 20% and 44 +/- 9% for TCMTB doses of 15, 75 and 150 mg/kg, respectively. Two doses, 75 and 150 mg/kg, caused diuresis in rats during the 1 week of dosing. During the 3-week TCMTB treatment, rat liver microsomal CYP enzyme profile was not significantly changed. Urine samples of sawmill workers exposed to TCMTB were collected after their work shifts for exposure assessment. TCMTB could not be detected in the urine samples of exposed workers. Most concentrations of 2-MBT were below the limit of the detection, 0.12 mumol/l, the concentrations were 0.12-0.15 mumol/l only in few cases. The determination of 2-MBT in urine, when a sample is taken immediately after a work shift, is a suitable indicator of workers' exposure to TCMTB.

CYP enzymes catalyze the formation of a terminal olefin from 2-ethylhexanoic acid in rat and human liver

1. The metabolism of 2-ethylhexanoic acid (2-EHA) was studied in rat, mouse and human liver microsomes in vitro. The metabolites of 2-EHA were identified as methylated derivatives by gas chromatography-mass spectrometry. 2. 2-Ethyl-1,6-hexanedioic acid was the main metabolite produced in rat, mouse and human liver microsomes. Unsaturated 2-ethyl-5-hexenoic acid, a terminal olefin, was produced only in human liver microsomes and phenobarbital-induced rat liver microsomes. The cytochrome P450 (CYP) inhibitors metyrapone, SKF 525A, triacetyloleandomycin (TAO), quinidine and the cytochrome P450 reductase antibody abolished its formation both in rat and human microsomes. 3. The metabolites were analyzed also in vivo in urine of 2-EHA-exposed rats and in urine of sawmill workers exposed occupationally to 2-EHA. Both rat and human urine contained 2-ethyl-1,6-hexanedioic acid as the main metabolite and also 2-ethyl-5-hexenoic acid. Metyrapone, SKF 525A and TAO all decreased drastically the formation of 2-ethyl-5-hexenoic acid in the rat. 4. The data indicate that (1) several CYP families (CYP2A, CYP2B, CYP2D and CYP3A) could be responsible for the hepatic metabolism of 2-EHA, (2) the same metabolites were formed in rats and man and (3) an unsaturated terminal olefin, 2-ethyl-5-hexenoic acid is formed in the liver.

Reactions of hydrated formaldehyde in nasal mucus

Formaldehyde is a well known toxic air impurity affecting the upper respiratory tract. It rapidly forms methylene glycol in water. Reactions of the hydrated formaldehyde with nasal mucus were studied by C-13 NMR spectroscopy. In the NMR spectra methylene glycol dominated and only minor signals from possible reactions were observed. This finding suggests that nasal mucus effectively protects nasal epithelium against formaldehyde.

Biological monitoring of deltamethrin exposure in greenhouses

This study examined the possibility of using biological monitoring to assess deltamethrin exposure among greenhouse workers. The synthetic pyrethroid deltamethrin was sprayed in five greenhouses by cold for generators, and the exposure was biologically monitored by analysing the concentration of its metabolite, 3-phenoxybenzoic acid, by a gas chromato-graphic method after derivatization with pentafluorobenzyl bromide. 3-Phenoxybenzoic acid was found in the urine of two of the ten workers studied. The urine concentration of the metabolite varied from 2.4 to 51.7 micrograms/l. These results show that 3-phenoxybenzoic acid is suitable for biological monitoring for the assessment of exposure to deltamethrin.

Exposure to glycols and their renal effects in motor servicing workers

Ten car mechanics frequently exposed to glycol-based cooling liquids were followed during a workshift. Airborne ethylene and propylene glycol concentrations in the car mechanics' environment were measured. The car mechanics gave urine samples after the workshift and their excretion of ethylene glycol, propylene glycol, oxalic acid, calcium and ammonia was analysed and compared to that of unexposed office workers. Urinary succinate dehydrogenase activity and glycosaminoglycans were also measured in both groups. Airborne ethylene and propylene glycol concentrations in the car mechanics' environment were negligible. Urinary ethylene glycol excretion in exposed workers was significantly higher than that in unexposed workers, but propylene glycol excretion was at the same levels as in controls. In the exposed group, the excretion of the end metabolite of ethylene glycol, oxalic acid (47 +/- 11 mmol/mol creatinine, mean +/- SD, n = 10) differed slightly from that of controls (36 +/- 14 mmol/mol creatinine, mean +/- SD, n = 10). Urinary excretion of ammonia was higher among exposed workers than office workers. The excretion of calcium did not differ from that of controls. A marginally decreased urinary succinate dehydrogenase activity was found in the exposed men. The excretion of glycosaminoglycans was significantly lower in exposed workers. Therefore, it seems that ethylene glycol is absorbed by skin contact. The internal body burden is associated with oxaluria and increased ammoniagenesis typical of chronic acidosis.

Workers' exposure to airborne bacteria and endotoxins at industrial wastewater treatment plants

A study of sewage workers' exposure to airborne culturable bacteria and inhaled endotoxins was performed at nine waste-water treatment plants that treat mainly industrial effluents. Airborne endotoxins were collected on glass fiber filters and analyzed using a chromogenic limulus assay. Endotoxin concentrations measured in the immediate vicinity of the waste-water treatment process varied from 0.1 to 350 ng/m3. The eight-hour time weighted average concentrations of endotoxin to which workers were exposed exceeded the suggested exposure limit (30 ng/m3 endotoxin) at four of the plants. Air samples of culturable bacteria concentrations varied between 10 and 10(5) colony-forming units/m3. Of the particles carrying culturable bacteria, 88% had an aerodynamic diameter of less than 4.7 microns. The most common genera of airborne gram-negative bacteria were acinetobacter, citrobacter, enterobacter, klebsiella, and pseudomonas. High levels of exposure to bacteria and bacterial endotoxin usually were related to certain phases of the treatment process. The microbiological contamination of air was highest near the inlets where incoming wastewater entered the basins, in the sludge treatment area, and inside the biofilter tower. In these spaces it is necessary to control and reduce exposure to airborne bacteria and endotoxin at wastewater plants.

Urinary biochemistry in occupational exposure to glycol ethers

Glycol ethers and glycol ether acetates are dehydrogenated to alkoxyacetic acid congeners which may serve as biological indicators of exposure. The ethereal bond may also be cut in an oxidation reaction catalyzed by the mixed function oxidase. In case of ethylene glycol, the eventual endproduct is oxalic acid. Urinary oxalic acid and alkoxyacetic acid excretion together was found to relate to the decrease of the succinate dehydrogenase activity (SDH) as an indicator of renal mitochondrial effects. The excretion of ammonia by exposed workers was doubled as compared to controls. The excretion of chloride was found to be smaller in the exposed than in controls. The excretion of calcium and glycosaminoglycans (GAG) among exposed workers were similar compared to controls.

Airborne endotoxin concentrations in different work conditions

Workers from various occupations have described symptoms of upper respiratory tract, gastrointestinal tract as well as eye and skin irritation. Exposure to endotoxins may cause these symptoms. Structural differences of endotoxins from different working environments are present on the sources of Gram-negative bacteria.

Relationship between bacterial counts and endotoxin concentrations in the air of wastewater treatment plants

The relationship between bacterial counts and endotoxin concentrations in air samples was studied. Selective EMB medium favored the growth of a larger portion of airborne gram-negative bacteria than LES Endo or MacConkey medium and was a good predictor of the endotoxin levels determined with a chromogenic Limulus assay of the air of wastewater treatment plants. The bacterial counts determined with nonselective media correlated poorly with airborne endotoxin levels; however, R2A medium yielded higher viable bacterial counts than TYG medium. Direct counting by epifluorescence microscopy yielded the highest bacterial counts, but no correlation was obtained between total bacterial counts and endotoxin concentrations.

Kinetics and renal effects of formic acid in occupationally exposed farmers

Twelve male farmers (38 +/- 14 years of age, mean +/- SD) were exposed to 7.3 +/- 2.2 mg formic acid/m3 for 8 h in the silage making (mean +/- SD, N = 12). Each gave urine samples immediately, 15 h and 30 h after the end of the exposure. The excretion of formate was linearly related to the exposure 15 and 30 h after the exposure. Exposure increased renal ammoniagenesis and urinary calcium at 30 h post-exposure. Both biochemical effects may be explained by the interaction of formic acid with the oxidative metabolism of renal tubular cells, as formic acid is a known inhibitor of the cytochrome oxidase. In view of these renal effects, the current hygienic limits may not entirely protect exposed individuals.

Methanol and formic acid toxicity: biochemical mechanisms

Metabolism of methanol, methyl ethers, esters and amides give rise to formic acid. This acid is an inhibitor of the mitochondrial cytochrome oxidase causing histotoxic hypoxia. Formic acid is a weaker inhibitor than cyanide and hydrosulphide anions. The body burden of formate in methanol poisoning is high enough to cause acidosis, and other clinical symptoms. Part of the protons can be attributed to formic acid whereas the most significant acid load results from the hypoxic metabolism. The acidosis causes e.g. dilatation of cerebral vessels, facilitation of the entry of calcium ions into cells, loss of lysosomal latency and deranged production of ATP. The latter effect seems to impede parathormone-dependent calcium reabsorption in the kidney tubules. Besides, urinary acidification is affected by formic acid. Its excretion causes continuous recycling of the acid by the tubular cell Cl-/formate exchanger. This sequence of events may partially explain an accumulation of formate in urine. Occupational exposure to vapours of methanol and formic acid can be quantitatively monitored by urinary formic acid determinations. Formic acid toxicity may prove a suitable model for agents causing histotoxic hypoxia.

Evaluation of workers' exposure to 2-ethylhexanoic acid (2-EHA) in Finnish sawmills. A field study

Exposure to a new wood preservative agent (Sinesto B), whose active ingredient is 2-ethylhexanoic acid (2-EHA), was determined by urinalysis of the parent chemical and its metabolites in workers employed in four Finnish sawmills. The excretion of these chemicals was compared with the inhaled dose analyzed in air samples collected at the breathing zone and with the percutaneous absorption determined by epicutaneous sampling. The main route for entrance of 2-EHA into the body is by breathing, because the urinary concentration of 2-EHA correlated linearly with the concentration of 2-EHA in the air (r = 0.70). There was no correlation between skin contamination and urinary levels of 2-EHA. In most cases the highest urinary concentrations of 2-EHA were found immediately after the work shift. Therefore, in order to evaluate a worker's exposure, the urine sample has to be taken immediately after the work shift. Workers in cranes had the highest exposure to 2-EHA, which describes well the evaporation of Sinesto B into the ambient air. 2-EHA was not found in the urine of non-exposed workers.

2-Ethylhexanoic acid inhibits urea synthesis and stimulates carnitine acetyltransferase activity in rat liver mitochondria

Adult male 3-month-old Wistar rats were given 0, 100 mg/l, 1, 5 or 10 g/l 2-ethylhexanoic acid in their drinking water for 20 days. Their daily consumption of contaminated water was measured and compared with the free acid found in their 24-h urine samples. The excretion was dose and time dependent. At the termination of the experiment, liver mitochondrial carnitine acetyltransferase activity was induced dose dependently and the citrulline synthesis in the urea cycle inhibited. Our results compare very well with the toxicity of a structural congener of the 2-ethylhexanoic acid, i.e. valproate, an antiepileptic drug.

Kinetics and toxic effects of repeated intravenous dosage of formic acid in rabbits

Adult male rabbits were injected i.v. with 100 mg buffered formic acid per kg body weight daily for 5 days with 24 h between the doses. The fifth dose was labelled with 14C-formic acid. Rabbits were killed 1, 2 and 20 h after the last injection. The highest formic acid concentrations were found one hour after the fifth dose. Total formic acid concentrations were always higher than radiometrically measured. The maximum concentrations of formic acid in brain, heart, kidney and liver were roughly similar to the concentration which inhibits half of the cytochrome oxidase activity in vitro. Histological studies clearly demonstrated the histotoxic changes at cellular level. Calcium deposits were detected in all organs of the injected rabbits. They were absent in control animals. It seems that the formic acid metabolism is slow and that it may cause sufficient hypoxic acidosis to allow the calcium influx and cellular damage.

Effect of renal formic acid excretion on urinary calcium and ammonia concentrations

Intragastrically given formic acid (300 mg/kg) caused high urinary formate concentrations in rabbits with continuously decreasing urinary pH up to 30 h after the dose despite the fact that the bulk of the formate in urine was excreted within 15 h. Urinary formic acid inversely correlated to urinary ammonia in 23 workers occupationally exposed to methanol or formic acid so that the delayed urinary acidification could have been caused by the effects of formate on renal ammonia genesis. The urinary excretion of calcium was linearly correlated to the formic acid excretion by the same subjects. The latter effect may have been caused by interferences with the tubular reabsorption mechanisms for the calcium ion.