EVALUATION OF MERCURY ATMOSPHERIC CONTAMINATION IN A DENTAL OFFICE USING TRANSPLANTED SPANISH MOSS (Tillandsia usneoides, L.): ESTABLISHING ENVIRONMENTAL BACK GROUND LEVELS.

 

Calasans,C.V.C.; Carvalho, C.E.V.; Primo,W.S., Cavalcante, M.P.O.; Souza, C.M.M. (Laboratório de Ciências Ambientais, Universidade Estadual do Norte Fluminense, Campos dos Goytacazes, Rio de Janeiro, 28015-620, Brazil, Tel: +55 24 726-3909, Fax: +55 24 726-3720); Castanheira, C. (Prefeitura Municipal de Campos dos Goytacazes, Campos, R.J., Brazil). carvalho@cbb.uenf.br .

 

Abstract

The aim of the present study was to monitoring the air quality in a dental office by the use of transplanted Spanish moss (Tillandsia usneoides). Transplant technique consists of transferring plants from unpolluted sites to the area that will be monitored and it was successfully employed at some industries (chlor-alkali, zinc smelter) to evaluate atmospheric heavy metals contamination. Mercury background concentrations were determined by analysis of 10 plant samples collected at rural areas. Samples (dried at < 40oC) were wet digested using a H2SO4:HNO3 mixture (1:1 v/v), H2O2 and KMnO4. Mercury determinations were performed by ICP-AES (Varian Liberty II). Analytical method reliability was evaluated by digesting a Standard Reference Material (SRM 1515 Apple Leaves) and Hg concentration obtained (41.9 ±  3.6 ng.g-1) was in accordance to the certified value (44.0 ±  4.0 ng.g-1). The Spanish moss had a mean Hg value of 82.5 ±  21.0 ng.g-1. Since Hg background level was established, the next step will be the exposure of the plant in the dental office.         

 

Introduction

 

            Dental offices are among the main sources of amalgam to the environment. Dental amalgam is a mixture of silver-tin particles, liquid mercury, copper and zinc. Silver amalgam consists of 43 to 50 % Hg and during its preparation some losses of Hg to the atmosphere may occur due to the high vapor pressure of elemental mercury (Hg0). The studied dental office is a small, hot and not well ventilated room where the amalgam is prepared in a mortar and Hg in excess is removed by squeezing the amalgam in a cloth. This procedure yields some Hg droplets in the working bench.

            The use of lichens and mosses to monitoring air quality had been proposed by several authors (Steines & Krog, 1977; Rühling and Tyler 1968, 1969, Goodman and Roberts, 1971; Hawksworth & Rose, 1970). These organisms have an exceptional capacity to retain inorganic ions. As minerals enters these plants almost entirely through the air they are useful indicators of atmospheric pollutants (Steines & Krog, 1977).

           

Material and Methods

 

Plant samples were collected by hand in the north of Rio de Janeiro State at the Municipality of São Fidélis in Barro Branco locality. Ten sub-samples were collected in different trees in the surroundings. Each of these sub-samples were packed in distinct plastic bags during transport to the laboratory. In the laboratory, the plants were separately oven-dried (40ºC), powered in porcelain mortar and wet digested in triplicate, using the procedure described by Bastos (1998).

Analytical method reliability was evaluated by digesting a Standard Reference Material (SRM 1515 Apple Leaves) and Hg concentration obtained (41.9 ±  3.6 ng.g-1) was in accordance to the certified value (44.0 ±  4.0 ng.g-1). Mercury was measured in an ICP/AES (Varian, model Liberty II) with vapor generating accessory. The detection limit of the method used was 0.5 ng/g-1.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 1. Sampling site location is indicated by dashed arrow.

 

 

Results and Discussion

 

            All mercury data obtained in the sampling station is presented in Table 1 with the respective variation coefficient and standard deviation.

            Mercury concentration in all samples varied from 55.4 to 127.1 ng.g-1, with an average concentration of  82.5 ng.g-1. The standard deviation for each sub-samples was low with and average of 6.2. The variation coefficient between duplicates was also low with an average of 7%. (Table 1). Although the coefficient of variation and the standard deviation between each sub-samples duplicate was low, the standard deviation among all 10 analyzed samples was very high (21%).

            Comparing our results to the study develop by Calasans and Malm (1997) with the same species, it is possible to observe similar values (100 ng.g-1) described as the background from a rural area. Comparing our results to other values described by the literature as background for lichen and moss: 70 to 480 ng.g-1 for the lichen H. physodes (Lodenius, 1981); 60 to 90 ng.g-1 for the feather moss P. schreberi (Rinne & Estrup, 1980), it was possible to observe that they are also similar to our results, and also presented high standard deviation.

            Although mercury contamination in the North of Rio de Janeiro region had already been reported by some authors (Primo et al., 1999; Souza, 1994; Lacerda, et al. 1993; Câmara, 1986), mainly due to past gold mining activities and the large use of mercury fungicides on the sugar cane plantations (banished in the beginning of the eighties), the observed Hg concentrations in T. usneoides did not showed any high values.  

            According to Primo et al. (1999) the old harvesting methodologies used at the sugar plane cane plantations, like burning the sugar cane fields before harvest increase the Hg atmospheric transport to remote areas. This hypothesis developed by Primo et al. (1999) is not confirmed by the concentrations found in Tillandsia usneoides at the region. These hypothesis was probably valid in the past when Hg fungicides were widely used but in the present our results showed that atmospheric Hg deposition is low.

 

Table 1. Mercury concentration in Tillandsia usneoides and respective standard deviation and variation coefficient from the ten sampling sites.  

Sample number

Hg (ng.g-1)

Standard deviation

Variation coefficient (%)

1

71.8

2.4

3

2

89.3

9.2

10

3

67.4

3.9

6

4

59.9

0.1

0

5

92.1

4.8

5

6

55.4

0.9

2

7

76.1

1.6

2

8

127

15.2

12

9

94.5

13.3

14

10

91.5

10.8

12

Average

82.5

6.2

7

 

 

Conclusions

            Based on the above arguments it was possible to assume that, although high variation on the Hg concentrations in samples collected in the same areas was observed, this variations are probably due to natural factors. The environmental contamination of the samples was rejected based on the background concentrations described by other studies, carried out with the same plant or with other species, that presented similar concentrations. Although, the sampling area was very restricted it was possible to establish an average Hg background levels for Tillandsia usneoides for the region (82.5 ± 21.0 ng.g-1). However, we reinforce the necessity of extending  the sampling area.

 

References

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Acknowledgments

            The authors would like to thanks the technicians Denise Nogueira de Souza and Cristina B. Siqueira for helping in the laboratory procedures..