The Science of the Total Environment, 71 (1988) 389-400 389 Elsevier Science Publ ishers B.V., Ams te rdam - - Pr in ted in The Nether lands

EFFECTS DERIVED FROM LONG-TERM LOW-LEVEL CHROMIUM EXPOSURE IN FERRO-ALLOY

METALLURGY. STUDY OF ABSORPTION AND RENAL FUNCTION IN WORKERS

V. FOA, L. RIBOLDI, M. PATRONI, C. ZOCCHE~TI, C. SBRANA x and A. MUTTI ~

Institute of Occupational Medicine

Clinica del Lavoro L. Devoto

University of Milan, Istituti Clinici di Perfezionamento

Milano - Italy

XServizio di PISLL, USL, No.2, Avenza (Carrara) - Italy

XXInstitute of Internal Medicine and Nefrology

Department of Occupational Medicine, Laboratory of Industrial Toxicology

University of Parma, Parma - Italy

ABSTRACT

Ferro-chromium production is based on the use of chromium oxide (III) and it

is generally accepted that chromium in this form is not able to cross biologi-

cal barriers. However, the data on the toxic and carcinogenic effects of hexa-

valent chromium in man are now firmly~ established. Some studies have questioned

these data, calling for a clarification as to whether exposure to trivalent

chromium can also produce human effects, perhaps with different latency time. A study was carried out on the exposure conditions (type and degree) in a

ferro-chromium foundry that had been in operation since 1972. The absorption

levels in the working population of the foundry, and the possible toxic effects

on the kidney have been investigated.

A total of 236 workers (142 employed in production departments, 33 office

workers and 61 sub-contractor employees) were examined with measurement of the

indicators of dose (urinary-chromium) and of effect on the kidney (albumin,

retinol binding protein, and renal tubular epithelium antigens in the urine).

Environmental hygiene measurements showed relatively low values of total

chromium in the air (always < 0.160 mg/m3). Hexavalent chromium was absent or,

if present, at levels below the sensitivity of the analytical method used

(0.001 mg/m3). The values of urinary chromium measured at the beginning and at

the end of the working day and at the end of the work shift were always

< 5 ug/g creatinine, which has been proposed as a biological limit in chromium

exposure. However, differences were observed between groups of subjects

employed on different jobs, which is indicative of an absorption process vary-

ing according to the degree of exposure. The indicators of effect did not

reveal any renal impairment, even early, that could be attributed to the toxic action of chromium.

INTRODUCTION

The general toxicology of chromium compounds has been dealt with in a large

number of experimental and human studies, especially in view of the differences

that have been observed in the toxicity of the many compounds in which chromium

is used. On this subject, exhaustive reviews are available (refs.l-4) which

0048-9697/88/$03.50 © 1988 Elsevier Science Publ ishers B.V.

390

confirm that hexavalent chromium is more toxic due to its power of crossing cell

membranes. Trivalent chromium does not possess this property and, therefore,

accumulates mainly in the lung (ref.5) ; a minor part is, however, absorbed by

the organism (ref.6) and excreted, mainly via the urine, with extremely slow

kinetics.

There is some doubt about the potential toxicity of trivalent chromium,

especially the carcinogenic effects, which have now been adequately demonstrated

for some hexavalent chromium compounds (re f.3).

However, trivalent chromium has been shown to possess affinity for nucleic

acids where it appears to have a stabilizing action, but also the ability to

induce physical-chemical changes. In fact, some authors have suggested that the

trivalent form could be the ultimate mutagen or carcinogen (refs.7,8).

In the production of ferro-chromium, which is obtained by reduction of

chromite with coke, exposure should prevalently be to trivalent chromium. The

few studies made on health effects in working populations in this field have

given contradictory results (refs.9-11).

With the aim of improving knowledge of the toxicity of trivalent chromium,

we made a study on the working population of a ferro-chromium foundry, which

included assessment of the level and type of exposure, the degree of absorption

of the metal, short and medium term effects (skin, gastro-intestinal, kidney

and lung damage) and long term effects (study of the causes of death). This

paper reports the preliminary results of exposure and absorption levels, and

effects on kidney function.

MATERIALS AND METHODS

The study was carried out at a foundry that has been producing ferro-chromium

since 1972, by means of reduction of chromite with coke, with bauxite and

quarzite as fusion agents in triphase electric submerged arc furnaces.

A total of 236 subjects were employed at the plant, all of whom were males:

142 were employed on production, 33 were office Staff, and 61 were employed by

sub-contractors on production.

Age and length of exposure are shown in Table I. The population was on the

whole homogeneous both as regards age and length of exposure, except in the

subcontractor employees for which there was a more rapid turnover. A detailed

analysis was made of the production cycle, with a systematic study of the tasks.

For the study of environmental exposure, atmospheric concentrations of total

dust, total chromium and hexavalent chromium were measured. Total chromium was

determined by means of alkaline fusion in platinum crucibles with sodium

hydroxide and lead nitrate and, after cooling, solubilization in distilled

water acidified with hydrochloric acid. Analysis was performed using the atomic

absorption spectrophotometric technique.

TABLE i

Age and length of exposure in different categories of workers

391

Workers Number of Age Length of exposure

catetory subjects X SD ~ SD

Clerks 29 43 7 i0 5

Workmen 124 41 9 12 8

Sub-contractors 46 37 13 2 2

4 clerks, 18 workmen and 25 sub-contractors did not accept to submit to the

study.

Hexavalent chromium was measured by cold acid attack of the sample with

sulphuric acid 0.5 N and subsequent quantitative determination with the diphe-

nylcarbazide colorimetric method. The limit of detection for hexavalent chro-

mium was 0.001 mg/m 3. For the study of the levels of chromium absorption,

urine samples were collected at the beginning and end of the working day and

also at the end of the shift or working week.

For all subjects, sample collection was initiated on return to work after

at least two days off. Determination of urinary chromium was performed using

the atomic absorption spectrophotometric technique. To assess renal function,

the following urinary tests were used:

- albumin, as an indicator of glomerular function;

- retinal binding protein (RBP) as an indicator of tubular reabsorption capacity;

- renal tubular epithelium antigens (proximal convoluted tubule: BB50), as a

direct indicator of cytolysis and/or increased cellular turnover following

toxic damage.

The tests were performed on urine samples collected at the end of the last

working day of the shift or week, as it is presumed that any changes are more

likely to occur at such a time.

Determinations were made using the immunoenzymatic technique (ELISA) (ref.

16) for RBP and the monoclonal antibody technique for BB50 (ref. 13).

Students' tests for paired data, variance analyses (when there were more

than two groups under comparison) and multiple regression analysis were used

for statistical analysis of the data.

Where the distribution of the values was so asymmetric as to preclude appli-

cation of the above statistical tests, logarithmic transformation of the data

was employed. In all such cases, transformation ensured applicability of the

tests.

RESULTS

The results of determinations of total dust and atmospheric chromium (total

and hexavalent) made at the different workstations are reported in Table 2.

392

TABLE 2

Airborne concentration of total dust, total chromium and hexavalent chromium

in work positions

Sample Total Total % chromium Hexavalent

location dust chromium in dust chromium mg/m 3 mg/m 3 mg/m 3

Conveyors-belt and 6.85 0.158 2.3 < 0.001

scales room

Electrode lining 6.66 0.109 1.6 < 0.001

Furnace load 2.12 0.024 i.i < 0.001

Casting 2.17 0.021 0.9 < 0.001

Crushing 3.28 0.117 3.8 < 0.001

Selection 1.66 0.020 2.0 < 0.001

The values were always relatively low and in any case well below the limits

currently considered as acceptable for exposure to chromium. The highest values

were found in the conveyor belt/scales area (arrival area of raw material for

loading in furnaces from conveyor belts); in the electrode lining replacement

(area located above the furnaces) and in the alloy crushing area.

The levels of hexavalent chromium were below the sensitivity of the analy-

tical method (0.001 mg/m 3) and, therefore, negligible.

Dispersion of other pollutants (asbestos fibres, estimated with AIA stan-

dardized method and sulphur dioxide and carbon monoxide, estimated with gas

detector tube) which were measured in order to make a more complete assessment

of the exposure hazard, was negligible (asbestos ~ 0.01 ff/cm3; SO 2 and CO

traces).

In the areas already mentioned (conveyor belt/scales; electrode lining re-

placement), total dust and respirable fraction exceeded the TWA, taking into

account the silica content of the dusts (usually ~ i% but never > 2%). Like

the environmental pollution levels, the urinary chromium levels were also

rather low (Table 3). Only in 4 subjects (3 maintenance men and one furnace

loading operator) were observed values > 5 ~g/g creatinine (all in the end-of-

shift sample), which is currently considered as a biological exposure limit.

In all groups, the mean end-of-day value was higher than the morning value,

suggesting a process of chromium absorption related to working activity; ab-

sorption was, however, very limited, never exceeding a value of 1.7 ~g/g

creatinine.

The end-of-shift values were similar to those of the end-of-day levels. It

can, therefore, be presumed that renal clearance of the metal is low, thus

indicating low accumulation and, therefore, low exposure over time. Age and

length of exposure did not seem to have any influence on the results since they

were homogeneous in the various groups.

393

TABLE 3

Mean values of urinary chromium (ug/g creat) in different categories of

workers, at different times in the work shift

Worker X ± SD/ % < 5 ~g/g Cr

category U2 U3 U4

Clerks 0.60±0.59 100 0.69+0.40 i00 0.58+0.55 i00 Workmen 0.94±0.74 I00 1.21±i.01 x I00 1.25+1.30 97 Sub-contractors 0.77±0.46 i00 0.96+0.71 i00 1.05±0.71 98

U2 = beginning of the first working day; U3 = end of the first working day; U4 = end of the last day of work shift

paired t-test (U3-U2): p = < 0.003

Job analysis (Table 4) confirms the following trend: absorption occurs in all

groups except ferro-chromium sorters (not reported in Table 4). The extent of

this phenomenon, although very limited, is greater in the raw material input

operators, scales, furnace assistants and crushing operators, dust elimination

operators and maintenance men employed on sub-contracted building work. This

finding agrees with the higher levels of pollution found in the scales area,

in the area above the furnaces and in the ferro-chromium crushing area.

The mean values of the indicators of possible renal impairment were within

normal limits (Table 5). Differences between groups were observed for RBP

(which was relatively higher in the sub-contractor employees) and BB50 (which

was slightly higher in the office workers); the percentage of subjects with

values > 95 ° percentile was similar to that observed in the non-occupationally

exposed population. These subjects (Table 6) did not show high levels of

urinary chromium and only 3 of them were employed on jobs where a higher degree

of absorption was observed (crushing, dust elimination and building maintenance

work).

Job analysis (Table 7) confirmed the overall similarity of the mean urinary

albumin values with higher RBP values among scales, crushing, routine mainte-

nance and dust elimination operators and among building and machine maintenance

workers employed by sub-contractors. This finding, compared with the urinary

chromium results, only partially agrees with previous observations: no par-

ticularly higher chromium absorption was observed among routine maintenance

workers and sub-contractor machine maintenance workers.

Multiple regression analysis (Table 8) between urinary chromium, age,

length of exposure and renal damage tests did not reveal a significant corre-

lation between these variables.

394

tM

O

4~

r~

(1)

g 4

4~

0

o

0

4J

g 4

0

21

0

O

~4

.5

b

-,-i Iq 4~ rd ~4

J

o?

8

D

0

0 r~ o

• 0 0 0 ° 0 0 0

o o o o o o o o ~ ~

? ? o ? ? ? ? o o ? ?

o ~ o o ~ o ~ ~ o

~ ~ o ~ o

0 , . , . . . , o o o o o o o ~ S S o

~ ~ o o ~ ~ o . . . . . . . 0

o o o 0 o o o o S o o I I I I I I

d d d d d d d d o o o I I I I I I I I I

~d

"~ , - I ~' J~ ~ ~ ~' I ~} I " ~ I 0

4~ q4

0

4~

,'-4

4J

r~

II

' D

r~

O

4J

IN

tM ~

r~

II V

O

O N V

4.3 II

tl~ ,o

0 ~

t ~ 4J

.,~ ~ ~ 4a

-,4

395

$ u'3

m rn

r~

-,-I

4~

(9

~4

4~

r~

-,-4 (9

4~ 0

O~

,..Q

r~

4_1

~ °

) . ~ ~ o

4~

~ r-, , l J

o

(9

r~

t ~ 2:k

v

A O

tY,

v ~

Im

1.4

u 3

d

o; 0o

II c'-I ~

o

• °

o 4~ o

43

~ 0~ 43

i D ~ ° ° • ~ l ~ i ~ = o o

~ II II v o

m ~ ,° D.I

~ Z

en

O~

r..)

o Z

396

r~

.,-t

d) 1.4

r~

4J

O

~4

.tJ

g o ~

0 -,-t

-,H r~

Z ¢1

o

~L

-,-t

0

-,'4 ~4 m

o o o

~ D

• ; o o

0 0 0 0

~ O 0 ~ O ~ O ~ O ~ O ~ O ~ O

. . . . . . 0 0 ° °

~ o o ~ o o o ~ o

~ g d ~ d g g g g d ~ d o

• • I I . . . . o d d S d d

~ 4 d ~ 4 d d 4 d o ~

~ 0 ~ 0 ~ ~ ~ 0 , . t 0 . 0 , , , 0

~ 0 ~ ~ 0 ~ 0 0 I l l O l l O O Q I

rd

D

,t~

t ~

o,I rd

IN U

.~ ~0 ~

D r ' II

~ o ~

v "-~= ~

, 0 ~

-,-.I c'.

o ~ ~

0 ~ ,-~

4 N

0

397

~D

O', -,4 ,.~

.,-t

4~

' t J

e"

-,4

O

t ~ c~

n:J

-,'4

.5 (1)

rn

m o

ID

o 4.4 , ~ kul

," , tJ

m

0

~ ~ ~ ~ o

~ 0 0 ~ 0 ~ 0 0 ~ 0

SdSddSSd ~ o S I l l I I

, , . . . , . , .

, r -,-I

,r" . 0 '4-I ~ I/) I/)

,o .~ .~ ~ . ~ -~, o ~ ~'~-.~,~

o ~ , ~ . ~ ~ o o -.-I . - I I~ 4 -I ~ I/~ ~ I I

u ~

.~ o ~ , . l J

t ~ I..i O • " ' 4J -,-4

• o ° I / ) °

• o °

II II U

I=I I~ o

m

n .

0

c~ ¢) ¢)

I1) U

-H ~4

398

~4

X

0

o

c~

0 44

m

~4

~4

r~

4a c

c

O~ CO O~ ~ O~ ~ ~ L~

0 0 0 0 0 0 0 0 0

~ o ~ ~ ~ ~ ~ ~ ~

o o o o o S o S S

0 0 0 0 0 0 0 0 ~-~

o o o o S o S o c~

I,-I

0 ~4 0 ~I 0 ~4 0 ~4 0 ~4 0 ~ 0 ~-I 0 ~ 0 N 0 0 0 0 0 0 0 0

0

4~ c~ ,-4

-,'4 e~

II II II

~D

0 0

-~ 0 ~

r-, m 4~

~ 4A 4~

~ tl.4 t~4 ~ 0 0 -~,

n

r. ~D

ID~O 0 ~ 0 0 ~ 0 0 " ~ 0 0 ~ 0 i ~ O i ~ O i ~ O 0 ~ 0

0 0 0 0 0 0

0 0 0

o o o

II II II

U r..) 0

399

DISCUSSION

The above data permits some preliminary observations to be made. In the

first place, it would appear that, under the manufacturing conditions present

in this factory, ferro-chromium metallurgy should not involve heavy exposure

to respirable chromium, and even less to hexavalent chromium. The concentra-

tions may have been higher in the past, but at present the values are well

below those observed by Axelson (ref.10) in the late 70's in a similar type of

plant in Sweden, and by Langard in Norway in the same period (ref. ll). Expo-

sure appears to be mainly, if not exclusively, due to trivalent chromium, i.e.

in the less absorbable form.

The levels of absorption were very low, especially if compared with those

observed in chromium electro-plating, special steel welding and chromate

production (ref.7) where exposure is to hexavalent chromium. The values found

in this study even appear not to be very different from those observed by other

authors in non-occupationally exposed subjects (ref.7).

Nevertheless, the absorption levels varied according to the job, thus

agreeing with the environmental pollution data. If a measurable exposure to

hexavalent chromium can be excluded on the basis of these environmental data

(further checks are under way), it must be assumed that total urinary chromium

is derived exclusively from absorption of chromium originally in the trivalent

state.

It would, therefore, appear that this form of chromium, too, can be ab-

sorbed, as reported by other authors (ref. 14).

The low levels of urinary chromium observed at the end of the shift indicate

a low renal clearance of chromium and, therefore, little or practically no

accumulation, in spite of long-term exposure.

The observations are confirmed by the fact that no early functional renal

damage was found, in spite of the reliability and sensitivity of the indicators

used. However, the tubular epithelium is capable of repairing any damage

suffered, by means of regeneration mechanisms, thus making it difficult to

detect effects of low-level chronic exposure.

We, therefore, cannot confirm whether the absence of renal damage was due

to non-toxicity to trivalent chromium, or to the low levels of exposure and

absorption observed, or to the more rapid regenerative power of renal epithe-

lium, which can repair damage before it becomes evident, at least with the

current methods of investigation.

However, the fact remains that in the working conditions under study, not

even initial renal impairment could be observed. The study of other possible

health effects (skin effects or effects of respiratory and digestive systems)

and of a possible excess of cancer would furnish further data which may help to

throw light on these points.

400

Research partially supported by European Coal and Steel Community Grant

Contract No. 7248-23-014.

ACKNOWLEDGEMENTS

We thank the Management Staff and Union Staff of Societ~ Ferro-Leghe

Apuana SpA for their free and continuous collaboration. Mrs. K. White for

linguistic revision of the text.

REFERENCES

1 S. Langard and T. Norseth, in: Friberg L., Nordberg G.F., Vouk V.G. (Eds.), Handbook on the Toxicology of Metals, Chromium, Elsevier, Amsterdam, 1979,

p.383. 2 S. Langard, in: Waldron H.A. (Ed.), Metals in the Environment, Chromium,

Academic Press, London, 1980, p.lll. 3 International Agency for Research on Cancer, IARC Monographs on the Evalua-

tion of the Carcinogenic Risk of Chemicals to Humans, Some Metals and Metallic Compounds, Voi.23, Lyon, 1980, p.205.

4 S. Langard, Biological and environmental aspects of chromium, Elsevier Biomedical Press, Amsterdam, 1982.

5 I. Franchini, A. Mutti, E. Cavatorta, C. Pedroni, A. Borghetti, in: Alessio L., Berlin A., Boni M., Roi R. (Eds.), Biological Indicators for the Assessment of Human Exposure to Industrial Chemicals, Chromium, Commission of the European Communities, Luxembourg, 1984, p.31.

6 A. Cavalleri, C. Minoia, Distribuzione nel siero e negli eritrociti e eliminazione urinaria del cromo in esposti professionalmente a cromo(VI) e cromo(III), G. Ital. Med. Lav., 7 (1985) 35-38.

7 T. Norseth, The carcinogeneticy of chromium, Environ. Health Persp., 40 (1981) p.121.

8 A. Peltier, Z. Elias, M. Demange, C. Cavelier, B. Herv4-Bazin, Exposition professionnelle aux compos4s du chrome, Cahiers de Notes Documentaires, INRS Paris, 105 (1981) 509-520.

9 L.V. Pokrovskaya, N.K. Shabynina, Carcinogenous hazards in the production of chromium ferro-alloys, Gig. Tr. Prof. Zab., I0 (1973) 23-26.

i0 G. Axelson, R. Rylander, A. Schmidt, Mortality and incidence of tumours among ferro-chromium workers, Br. J. Ind. Med., 37 (1980) 121-127.

Ii S. Langard, A. Andersen, B. Gylseth, Incidence of cancer among ferro- chromium and ferr-silicon workers, Br. J. Ind. Med., 37 (1980) 114-120.

12 S. Lucertini, P. Valcavi, A. Mutti, I. Franchini, Enzyme-linked immuno- sorbent assay of retinol-binding protein in serum and urine, Clinical Chemistry, 30 (1984) 149-151.

13 A. Mutti, P. Valcavi, S. Lucertini, T.M. Neri, M. Fornari, R. Alinovi, I. Franchini, Urinary excretion of brush-border antigen revealed by monoclonal antibody: early indicator of toxic nephropathy, Lancet, October 26 (1985) 914-916.