Evaluation of the current risk of lead poisoning in the ceramics industry.

Evaluation of the current risk of lead poisoning in the ceramics industry. Scand j work environ health 9 (1983) 463-469. The authors evaluate the current possibility of lead poisoning in the production of ceramic tiles, an industrial sector which has always been considered dangerous due to the use of lead-rich glazes. The study was conducted in nine plants, four of which were repeatedly monitored (five checks on 94 exposed subjects). The other five plants (for a total of 221 exposed subjects) were only checked once. An analysis of all the results showed a clear reduction in mean blood lead levels, which the authors believe was due to the use of glazes with less lead. The results obtained were generally satisfactory; they indicated a definite improvement in the situation with respect to the authors' previous investigations, even for jobs in which workers were more frequently exposed. The data overlap those observed in the production of artistic pottery, which has always been considered less dangerous.

The risk of lead poisoning in the ceramics industry has been evaluated in various ways in different countries by interested authors. In particular, exposure to lead in this industrial sector has been considered occasional (ll), among the less dangerous industries when compared with other work (20), or else important, although limited, as regards the number of cases (12).
In Italy in recent years many publications have shown high risk, both on the artisan and the industrial level (1,4,15,18). In this country risk has always been considered low in the production of artistic ceramics (2,6,10,19), and the good results obtained refer mainly to the reduced use, for economic reasons, of lead oxides in the materials used to cover or decorate ceramics (19).
Sometimes contrasting opinions on the real extent of risk are due to the fact that Istituto di Medicina del Lavoro, Universita di Padova, 1-35127 Padova, Italy.
Reprint requests to: Dr E De Rosa, Istituto di Medicina del Lavoro, Universita di Padova, Via Facciolati 71, 1-35127 Padova, Italy. very often "ceramic production" is indicated without the type of finished product being specified. In one type of work, there may be a high content of lead-rich glazes (eg, tiles) although they are used to a far smaller extent in artistic products or are even unnecessary for sanitary fittings.
Specific risk may thus vary as a function of the technology used, different glaze application methods, and the higher or lower percentage of lead in glazes. Other differences may be due to the kind of job done and the observance of personal hygiene.
The particular attention paid to the problem of lead in the Italian ceramics industry is linked to the largescale production of tiles for building -37 % of world production (16). In this type of work glazes with percentages of lead oxides varying from 5 to 50 % are used (16), and their preparation and application involve a decidedly high risk, as indicated by both environmental (17) and biological data (7).
Protective measures, personal hygiene, and improvements in the work environment may lead to a large reduction in risk (5,8). This was the conclusion reached in one of our previous works, and accord-ing to which we hypothesized that further preventive success could be obtained only through the reduction of the quantities of lead in glazes (8).
In glazes lead has such important technological and esthetic functions that, although compositions with less lead are currently being developed, the total elimination of this element is not yet possible, at least in the sector producing building tiles (16). Therefore, in the present study, we wished to verify the situation in the ceramics industry some time after our previous investigations in order to evaluate the current possibility of lead poisoning in this industrial sector.

Subjects and methods
In nine plants producing tiles for the building industry with a wet-glaze process, we checked 315 workers by means of blood lead measurements, believed to be valid as a parameter (14) of exposure.
In the first four plants (A, B, C, D) 94 workers were followed by means of five blood lead determinations. The second determination was made six months after the first, and the third, fourth, and fifth tests took place one, two, and three years, respectively, after the second. The total number of exposed workers in the examined plants was greater than that used for this study. However we thought it best to consider only those workers who underwent all the tests, who did not change type of job during the course of our investigation, and who were not absent from work for prolonged periods.
In the other five plants (El F, G, H, I) we checked the blood lead level of 221 workers only once, during the interval between tests 4 and 5 of the workers from plants A, B, C, and D. Table 1 shows the age and exposure of the subjects at the time of the first test of the workers from plants A, B, C, and D and at the time of the single test of the workers in plants E, F, G, H, and I.
The blood lead levels of the workers were measured according to the method of Westerlund-Helmerson (21) with the use of an atomic absorption spectrophotometer (Perkin-Elmer). The blood lead values of nonexposed subjects in our laboratory are the following: 1.3 (SD 0.4) pmolll for men and 1.0 (SD 0.4) pmol/l for women, as we have already reported (7).
The precision of the method was tested in our laboratory during the entire period of monitoring. The standard deviation of the method error from double determinations, as computed in our laboratory, has constantly remained between 0.09 and 0.15 pmolll. The precision of the method was estimated from measurements of the lead in three blood samples (one less than 1.0 pmol/l, one more than 2.4 pmolll, and the third inbetween) from 10 different runs. The average coefficient of variation was 4 (range 3.2-5.1) %. re) of the workers examined.

Plants E-F-G-H-I
: single testing The recoveries of added lead varied between 96.3 and 102.0 %.
In an Italian comparative study (1981)(1982) employing spiked samples, we tested the accuracy of the method. The results are given in table 2.
Student's t-test and t-test (paired) were used for the statistical analyses. value of the same subjects subdivided by plant. In all four cases, a statistically significant reduction in blood lead was found between tests 2 and 3, while a similar trend between tests 1 and 2 was only observed for plants B and D. Table 5 shows our subjects subdivided by job (excluding kiln workers, since there were only three of them). Between tests 1 and 2 the mean blood lead values showed Results ~~b l~ shows the results of the five blood rately. Table 4 shows the mean blood lead    4, and 5 all more or less over-lapped. Last, glazers always had blood lead levels which were higher, on the average, than those of workers in other jobs. Table 6 shows the data from the single measurement made on 221 subjects in plants E, F, G, H, and I. The table shows the mean blood lead levels with the relative standard deviation, both for the total number of subjects examined and for the subjects subdivided by sex and plant. In the latter case, the blood lead levels ranged from a minimum of 1.4 pmolll to a maximum of 1.7 pmolllnot substantially different from the values measured in plants A, B, C, and D in more recent checkups (table 4). Table 7 shows the mean blood lead levels of the same 221 subjects subdivided by job. The results confirm that glazing is the work phase leading to the greatest risk of exposure. Finally, table 8 shows the group distribution of the blood lead levels of the 94 repeatedly monitored subjects and of those tested only once separately.

Discussion
As already mentioned, the objective of our study was to verify the current risk of lead poisoning in the ceramics industry, with particular reference to wet-glazing in tile production. We believed this investigation to be topical since results obtained in follow-up studies on subjects exposed in this industrial sector gave the impression of a lower risk with respect to our previous experience (7, 8).  The results showed a clear decrease in the mean blood lead levels (well below the variability of the method) of the subjects between tests 2 and 3 and, to a less significant extent, between tests 1 and 2. The difference in tests 1 and 2 can be illustrated by a consideration of plants A, B, C, and D separately, as shown in table 4. In plants B and D the mean blood lead levels decreased from 2.7 (SD 0.9) and 2.6 (SD 0.8) pmolll, respectively, in the first measurement to 2.1 (SD 0.7) and 2.1 (SD 0.8) pmolll, respectively, in the second. The latter figures overlap those of plants A and C in both cases. Since plants B and D carried out environmental improvements (installation of aspiration equipment) in the interval between the tests and since the workers involved were also impressed with the importance of personal hygiene measures (all already practiced in plants A and C at the time of test 1) during this time, it may be deduced that the mean blood lead values between 2.1 and 2.2 ymol/l were the results obtainable with the technologies then used and with the observance of both environmental and individual preventive measures.
One year after test 2, a clear decrease in the mean blood lead levels was observed, both for all subjects and for a subdivision of them by sex (table 3), plant  (table 4), and job (table 5). The values we observed for test 3 did not differ for plants A, B, C and D; they also overlapped those of tests 4 and 5 without further significant reductions. It is evident that, during the course of the year between tests 2 and 3, a factor intervened which caused a clear improvement in the shiliion. In our opinion this factor cannot be environmental improvement or the adoption of persorlal hygiene measures demonstrating their effects with time, since in plants A and C these preventive measures were already being practiced and therefore any decrease in the blood lead levels would not have taken place together with that found in plants B and D, but previously.
In our opinion reduction in the lead content of the glazes was the determining factor affecting these results. The tendency towards abolishing or reducing the lead percentage of glazes has already been reported in the literature (16, 19), at least as a possible factor in the tile sector, and as a definite factor in artistic ceramic work.
Again, in the sector we examined, this tendency seems general since the blood lead levels of the 221 subjects examined once in plants E, F, G, H, and I, which used identical technology and in which environmental and personal hygiene preventive measures were in use, did not differ significantly (Student's t-test) from those obtained in the last checkup of the 94 subjects who had been repeatedly monitored.
Moreover no statistically significant differences emerged for any of the subjects examined, either between the two groups subdivided by sex or between the different types of jobs (glazing, decoration, selection, miscellaneous).
The checkups of the two groups of exposed workers were done in the same period, and, although we had no previous information on the group of 221 workers examined only once, we can state that the situation overlaps in the same period in all nine plants.
The final values show great general improvement, on an individual level too, as may be seen from table 8, which shows the blood lead values of the 315 subjects examined in the same period, which was our last.
As regards women workers, we found only three cases in which the level of 1.9 pmolll was exceeded. This value was the proposed maximum level recommended for women of fertile age during the Second International Workshop on Permissible Levels for Occupational Exposure to Inorganic Lead (22), and it has also been indicated as a threshold by the Occupational Safety and Health Administration of the United States (13).
In male workers, too, who generally undertake the more dangerous jobs, the results were also very satisfactory; in only one case was the recommended limit (2.9 pmolll) (22) exceeded.
At this point an important comparison may be made between data from the ceramic sector and those from one of our previous investigations on artistic pottery work (6). In the latter sector, for 274 exposed workers, we found blood lead levels of 1.3 (SD 0.5) pmolll and average values of 1.7 (SD 0.7) pmolll for glazers (60 subjects) and 1.2 (SD 0.3) pmolll for decorators (178 subjects).
Our data thus show that the risk of lead poisoning in tile production is similar to that in artistic ceramics, which has always been considered less dangerous and less polluting (7, 10) on the basis of biological results and as a consequence of the use of glazes with less lead (19).
As already stated, in the light of our results, this great improvement can only be explained by a reduction in the lead content of the glazes used. Recent literature does not show data on the percentages of lead used for glaze composition in the years included in our study, and thus we do not have any technological proof of our hypothesis. However, it should be observed that the current market trend in Italy is for the production of tiles with more opaque colors, and thus for lower contents of lead in the glazes also, since one of the most important properties of lead is to make the tile brilliant and glossy.
We believe that, in the future, high lead absorption will be found in tile glazers only occasionally and under particularly poor hygienic conditions. On the basis of our data, this consideration may probably be extended to include most Italian ceramic plants, although the biological monitoring of workers, albeit less frequently, will still be necessary. These positive conclusions regarding lead must not, however. lead to a slackening of the sur-veillance in these environments, mainly because of the presence of other toxic metals in glazes, eg, aluminum, titanium, nickel, copper, zinc, and, above all, cadmium, chrome and cobalt (3,9). We believe that professional risk in the ceramic tile industry is undergoing great change due to possible problems which have not been studied in depth previously, since attention was principally aimed at lead.