In the two follow-up studies (Rosenberg C, 2011, and Thuresson K, 2006), assess the impact of work environment changes on the PBDEs occupational exposure (Table IV).

Rosenberg C. et al. (2011)³⁹ evaluatedthe concentration of PBDEs on air using portable auto samplers on workers in different areas of a recycling plant in Finland in 2008 and after intervention in 2009. Zone A: plastic fractions grinding n=6 in 2008 and n=6 in 2009. Zone B: separation of materials with laser techniques and mechanic separation of metals n=7 in 2008 and n=5 in 2009. Zone C: manual dismantling and classification of waste and selective destruction of dangerous and valuable components n=5 in 2008 and n=4 in 2009. Zone D: batteries and dry accumulators by means of a dry and closed process of product grinding n=6 in 2008 and n=6 in 2009.

Dust samples were collected in the four areas and 46 air samples were taken with portable auto samplers during the first and second day, after the weekend and for a period of 191 to 408 minutes, in order to analyze the presence of PBDEs.

Industrial hygiene measures implemented were: improvements in ventilation systems by installing filters in the air pipes in order to prevent polluted air recirculate in working areas; in one of the areas a floor covering was installed in order to facilitate the cleaning and the cleaning service was intensified; a new grinding machine was installed, thus reducing the amount of dust released by this process and four of the workers used air purifiers breathing protection equipments.

After all these improvements, reduction in PBDE levels and deca-BDE 209 on air in all the recycling areas was observed. Congeners pattern was similar in areas A, B and D, where BDE 209 represents an average of 81% in 2008 and 91% in 2009 of the total PBDEs. In area C, BDE 209 was 66% (2008) and 62% (2009) of the total concentration of PBDEs.

Thuresson, K. et al. (2006)²⁸ evaluated the impact of industrial hygiene improvements on the occupational exposure in an e-waste recycling company in Switzerland. The shredder (considered the main PBDEs polluting focus) located in the dismantling room was placed outside the building. A specific ventilation system was installed, forcing the airflow from ceiling to floor in order to remove particles and dust from the air. Brooms were replaced by vacuum cleaners and the surface of working benches began to be cleaned with wet rags. All the improvement measures were totally installed by November 1999.

In 1997, a sample of 19 workers was studied and in 2000, once all the improvement measures were installed, 27 workers were studied. Those workers were classified in two groups: "Blue collar workers" (waste dismantling workers) and "White collar workers" (office workers separated from the dismantling area). A control group of 17 workers from an abattoir in the South of Sweden with little or no computer contact was established.

Non-parametric test were used for comparisons (Wilcoxon, U- Mann Whitney, Spearman). Bias control and confounding variables were not detailed. Samples were analyzed in two different laboratories.

Results show that, BDE 183 (p<0,05) and BDE 209 (p<0,001) serum levels have a significant reduction after the adoption of industrial hygiene improvements. Nevertheless, BDE 47 (p>0,25) and BDE153 (p>0,25) did not have a significantly reduction before and after the intervention, noticing a significant increase of BDE 153 in intra individual comparisons.

Octa- and nona-BDE levels in serum measured after the changes implemented in the company were significantly higher (p<0.01) than those obtained in the control group.

Zheng J et al. (2011)³³ studied PBDE levels and congener profiles in hair and dust in order to find out if dust was the main exposure route and to validate hair as specimen to evaluate the exposure to PBDEs (Table IV).

Two groups involved in e-waste dismantling were randomly chosen as exposure groups: First group was formed by 30 occupationally exposed e-waste recycling workers and the second group by 82 non-occupational exposed residents wich live in an e-waste recycling area. As control group, 29 urban residents and 32 rural residents were selected. Socio-demographic information was collected through a questionnaire. Inclusion and exclusion criteria were not described enough.

Statistical analyses included ANOVA and Pearson correlation test.

PBDEs hair levels and PBDEs levels of dust collected in workshops were higher on e-waste workers than on the other groups. BDE209 was the most abundant congener for all samples, although highest levels were found on e-waste recycling workers.

No correlation was found between levels on dust and hair (r=0,23; p=0,77). Occupational exposure has a positive correlation with hair PBDEs levels. Congener profile on hair is different than one on dust.

Table V summarizes the results of the analyzed studies following a cross-sectional design.

Kim B-H et al. (2005)²⁶, a cross-sectional study with reference group, studied PBDEs levels and congeners on 13 workers serum samples from an e-waste incineration plant in Seoul, Korea, with a reference group of 22 people.

PBDEs levels in the exposed population were significantly higher than in the reference group (p<0.05). BDE 183 was significantly higher on workers than in general population (p=0,01). No significant correlation between the concentration of PBDEs and age was found, although it was found between PBDEs and BMI. The study uses Principal Component Analysis (PCA) and the t-Student test.

Confounding variables and bias control is not properly described in the article.

With similar design, a cross-sectional study with control group, Bi X et al. (2007)²³ studied PBDEs exposure and health outcomes in China. They measure the concentrations and congeners profile on 26 serum samples from e-waste workers (Guiyu) and a control group formed by 21 people (Haojiang). Members of both samples were volunteers aged 18 to 81, 64% women and 36% men.

Confounding variables and bias control is not properly described. In the statistical analysis, Pearson correlation coefficient and U-Mann-Whitney were used.

PBDEs levels were three fold higher on occupational exposed group than in control group, difference which was statistically significant (p<0,00). No correlation was found between PBDEs serum levels and age. In the control group, no correlation between highly brominated PBDE congeners (BDE -197, -207, -209) and age was found.

They concluded that concentrations of PBDEs and highly brominated PBDEs detected on the exposed workers group in Guiyu were higher than those reported in European and American cities. Levels of PBDEs in the control group are possibly due to the recycling activity in Guiyu as a result of the atmospheric transport.

Qu W et al. (2007)²⁷ prepared a cross-sectional study with reference group. They investigate the association between the exposure to PBDEs on e-waste dismantling workers and the concentration of PBDEs in blood. Two exposure groups formed by volunteers were studied.

The first group was formed by 20 e-waste dismantling workers and the second group (non occupational) was formed by 15 farmers living 50km away from the dismantling region. The control group was formed by 20 women from a city in the South of China.

Levels of PBDEs on e-waste workers for significantly higher (p<0.05) than those on the other two groups, especially the levels of highly brominated congeners (hepta- to deca-BDEs), which were 11 to 20 times higher, but no for BDE-196, 203 and 206. In all groups, BDE 209 was the dominant congener. No correlation was found between serum levels of PBDEs and age, height or weight.

These results concluded that work exposure to PBDEs is associated with high levels of PBDEs in blood, especially for highly brominated congeners.

The cross-sectional study (with control group) of Athanasiadou, M. et al. (2008)²² examined PBDEs levels, congeners pattern and the presence of hydroxylated metabolites (OH-PBDEs) in serum samples on 162 garbage dump working children in Nicaragua. The sample was stratified in 5 groups, according to labour experience on dumps, place of residence and fish consumption: two groups with 64 children with occupational exposure (groups 1 and 2), two groups with 80 children with non-occupational exposure (groups 3 and 4) and a control group with 18 children (group 5), located in an area at 20 km.

The study included 32 women divided in four groups depending on the residence area (rural-fishing area -groups A and B- and urban area -groups C and D). The aim of the study was explore an association between PBDEs serum levels and fish consumption.

Confounding variables and bias were controlled by structured interviews, taking socio-demographic information, age, gender, fish consumption, place of residence, dietetic habits, work history and economic and cultural level. Statistical analysis was not described.

Ten PBDEs congeners were quantified. BDE-47 was he dominant congener and BDE-209 the less frequent. Occupational exposed children had higher serum levels of PBDEs and OH-PBDE metabolites than other groups. Women with low fish consumption had higher PBDEs levels than those living in fishing areas and consuming more fish.

Those authors found, PBDEs hidroxylated metabolites bioaccumulated in human serum. They finally concluded that serum levels of PBDEs and OH-PBDEs metabolites in occupational exposure children were significantly higher than those in serum samples from children living in urban áreas (althought they have high levels in serum, as well). It indicates that dust would be an important source of exposure to PBDEs in this populated area.

The oxidative damage to DNA has been studied by Wen S. et al. (2008)31 in a randomized cross-sectional study. Their aim was investigate the association between occupational exposure to PBDEs and oxidative damage to DNA, by measuring the levels of 8-OHdG (8-hydroxy-2-desoxyguanosine) in urine. 64 men aged 18 to 60 working for at least one year in two different industries devoted to e-waste dismantling were recruited.

64 urine and hair samples, pre and post work exposure, and 3 environmental samples of dust in workshops were analyzed.

Levels of 80HdG in urine were higher (p<0.05) at the end of the working day tan at the beginning. The more abundant PBDEs congeners were PBDE209> 47> 99> 183> 153, being deca-BDE the most abundant in all the samples (48.5-81.9%).

The aim of Yuan J et al. (2008)³⁶ was to analyze, by a cross-sectional study with control group, the association between the exposure to e-waste and thyroid alterations as possible inductors of genotoxic damage estimated through the measurement of micronucleated binucleated cells. They also determined the levels of 8-OHdG in urine, as biomarker of oxidative stress in exposed workers.

23 informal recycling workers with exposure to PBDEs were selected and a control group formed by 26 farmers.

The levels of workers PBDEs and TSH in serum were significantly higher than in the control group, with p<0.045 y p<0.01, respectively. Nevertheless, no significant differences were observed on the levels of urinary 8-OHdG in both groups. The authors state that this can be due to the study's low statistic power. The results show that working with e-waste is associated to high levels of TSH and higher presence of micronucleated binucleated cells.

Working with e-waste turned out to be a predictable variable of the concentration of TSH (OR 28, 95%, CI 5.90-132.83; p<0.000).

They reject the existence of association between PBDEs and oxidative stress. Methodologically, bias study and confounding factors is appropriate. The statistical analysis used t-Student, Pearson and U Mann-Whitney tests.

In other cross section study with control group, Zhao G. & col (2008)³² explored the exposure to PBDEs in e-waste recycling areas, studying the levels of congeners and OBDEs in hair samples of 44 workers implied in very rudimentary recycling processes, taking as control group 4 residents, from five different areas. Six soil samples were collected coming from 4 recycling activity areas, 3 soil samples from the control area and one e-waste sample (formed by cable coating, stuffing powder and chipped circuit boards).

These measures detected high levels of PBDE and BDE 209 (BDE 209 was the most often found congener) in all electronic waste samples, but specially in stuffing powder. PBDEs concentrations on soil were significantly higher in e-waste areas than in the control areas.

Levels of PBDEs in hair samples were significantly higher in the exposed areas than in control areas (p<0.05).

The general conclusion was that the average levels of PBDEs measured in the hair samples were coherent with the ones detected in the soil.

Confounding variables and bias controls are not well described. For statistic analysis they use the non-parametric U-Mann Whitney test.

Eguchi A. et al. (2010)²⁴ studied the presence of PBDEs' OH-BDE hidroxilated metabolites in serum on 5 e-waste recycling workers in India, aged 26 to 33, compared to a control group formed by 5 rural area inhabitants, aged 25 to 35.

Confounding variables and bias controls are not well described, as well as the statistic study.

Results showed that concentrations of PBDEs and BDE 209 in exposed workers were higher, although they were significantly higher only for BDE 209. The OH-PBDEs in the control group were significantly higher (p<0.05) than in the exposed workers.

BDE 209 was the dominant congener in all the samples.

The effect of the exposure to PBDEs on reproductive health is studied by Leung A. et al. (2010)¹⁹, who investigated the levels and pattern of PBDEs congeners in samples belonging to three types of specimens (breast milk, placenta and hair) from pregnant women and the potential risks on their children's health.

The exposure group was formed by 5 pregnant women living in Taizhou (e-waste recycling area), one of them working in the recycling industry. Participants were randomly selected. The control group was formed by 5 women living in a place located 245 km away from Taizhou.

Sociodemographic information, eating habits and over exposure to other substances were collected by means of a questionnaire.

X2, ANOVA, U-Mann-Whitney and Spearman correlations tests were used for the statistic analysis. Confounding variables control is not properly defined in the article.

Concentracions of PBDEs in the three samples (breast milk, placenta and hair) in the group of women living in the recycling area were much higher than those in the non-exposed group (p<0.05), specially in hair and breast milk.

Women working in the e-waste recycling had the second highest level of PBDEs.

There was a positive correlation between the concentrations of total PBDEs and low brominated PBDEs in the different types of samples gathered from the exposure group: hair and breast milk (r=0.998, p<0.0001), hair and placenta (r=0.995, p<0.0001) and breast milk and placenta (r=0.999 y p<0.0001). The congeners profile was the same in all samples. The dominant congener was BDE47.

A positive correlation was also found between body burden of PBDEs in women living in the e-waste recycling area and animal-origin food consumption (especially fish and seafood).

The estimated daily intake of PBDEs of a 6-month-old breastfed infant living in the e-waste recycling area was 572+-839 ng/kg body wt/day.

Concentrations of PBDEs in breast milk is studied by Tue, N.M. et al. (2010)³⁸ through a cross-sectional study with control group. They compared the exposure to PBDEs in women with levels of PBDEs in women breast milk (working or not) living in three places dedicated to electronic waste recycling: site 1 (batteries recycling), sites 2 and 3 (e-waste dismantling) and site 4 (typical urban area).

A questionnaire was conducted in 2007 to obtain information about sociodemographic variables (age, height, weight, number of childbirths, length of rest periods, occupation (working or not in the recycling industry), period of participation on recycling activities and food habits. These variables were statistically analyzed through the analysis of main components and multiple linear regression analysis. Data were transformed in order to achieve a normal distribution. Wilcoxon test was also used.

Levels of PBDEs in the e-waste recycling areas were significantly higher than in the batteries recycling area and in the control group. Congener profile was very similar in sites 1 and 2, with high levels of octa-, nona- and deca-BDE. Concentrations of BDE 209 were 50%. The profile of PBDEs was different in the reference area, where low brominated congeners were predominant, such as BDE-47 and BDE-153. BDE-209 was undetectable. There was a significantly correlation between levels of PBDEs and the development of recycling activities.

Wang H. et al. (2010)³⁵ studied with a cross-sectional design with control group, the effect of PBDEs released during e-waste recycling activities on the thyroid function. Three groups of workers were selected, each one with a different type of exposure. The first group (occupational exposure) was formed by 236 e-waste workers living in three different sites and randomly selected. The second group (non-occupational exposure) was formed by 89 people living around recycling sites. The control group was formed by 117 people working in a green plantation town.

Socio-demographic and health information were self reported by each participant.

TSH levels were significantly lower (p<0.001) in the e-waste workers group than in the non-exposed group. Nevertheless, no differences were found between e-waste workers and the people living around the recycling plants.

Age, race or smoking were not associated (p>0.05) with thyroid hormones levels. There was a strong positive correlation between levels of BDE126 and T4 concentrations (beta= 0.25, SE=0.10, p=0.0181) and BDE 205 and T4 (beta=3.27, S=0.97, p=0.001).

Authors also found that factors such as duration of exposure time, years of occupational dismantling and occupational mode of incineration had a strong positive correlation with the levels of PBDE (p<0.01). The respiratory protection presented a negative correlation (p<0.05) with the levels of PBDEs.

Methodologically, two independent sample-t-tests, covariance analyses were and linear regression analysis. Possible confounding factors, such as total lipids in plasma, sex, alcohol intake and age, were monitored.

Yu Z et al. (2010)³⁷ studied the presence of OH-PBDEs in blood of six e-waste dismantling workers as a possible indicator of highly brominated PBDEs metabolization.

The results identify 6-OH-BDE199, 6-OH-BDE196 and 6-OH-BDE206 in blood samples, concluding that highly brominated PBDEs can be oxidatively metabolized in OH-octa-BDE and OH-nona-BDE in human serum following a continuous long-term exposure to high concentrations of BDE-209.

There were no bias control measures or confounding potential variables described. Inclusion and exclusion criteria were not either detailed.

The association between exposure to PBDEs and levels of thyroid hormones is studied by Han G et al. (2011)³⁴ through a cross-sectional study with control group. A sample of 195 children with non-occupational exposure was collected from a site close to an e-waste recycling area and 174 children as control group from a further location.

It was statistically analyzed through a comparison of averages, using T-Student and linear regression tests

Levels of PBDEs of the exposed children were significantly higher than in the control group. In both groups a positive correlation between the concentration of PBDEs and the levels of TSH was found, being significantly higher in the control group. The health of children in the control area was better than in the polluted area, because PBDEs lead to increase the concentrations of these substances in serum, affecting the levels of thyroid hormones in children.

The link between occupational exposure to PCDD/Fs and PBDEs and the levels of these substances in hair was studied by Ma J et al. (2011)³⁰ by means of cross-sectional study with control group. Hair samples collected from 27 e-waste recycling workers were analyzed, all of them working in the industry for more than one year. The control group was formed by 27 people living in Shanghai, with no occupational exposure.

The information about their work history, health and hair characteristics (color, treatments) was surveyed.

Concentrations of PBDEs in e-waste recycling workers hair were three times higher than in the control group. The dominant congener in hair samples for both groups was PBDE 209. The control group had higher levels of BDE47 than the reference group.

An association was found between the congeners profile in hair and the congeners profile in the atmosphere within the recycling plant premises, concluding that hair samples could show exposures to PBDEs released from e-waste recycling operations.

Presence of metabolites of PBDEs is studied by Eguchi A et al. (2012)²⁵ through a cross-sectional design. They assessed the link between the exposure to PBDEs in e-waste recycling workers and levels of PBDEs and their metabolites (MeO-PBDEs -methoxylated PBDEs- and OH-PBDEs) in blood. They also analyzed the concentration of MeO-PBDEs in fish samples from marine and freshwater environments in order to find a potential association between fish intake and levels of MeO-PBDEs in blood.

Serum samples were collected from 25 e-waste recycling workers and 20 residents near a coastal area. By means of a personal interview they gathered the demographic information and everything related to their health and homes.

Concentrations of OH-PBDE and MeO-PBDE in serum from residents living near the coastal area were were significantly higher (p<0.05) than those in serum from e-waste recycling workers. Nevertheless, cocentrations of octa- to nona-BDEs anda octa-brominated OH-PBDEs were significantly higher in e-waste recycling workers than those in coastal population (p<0.05).

Concentrations of MeO-PBDEs in marine fish were significantly higher than those in freshwater fish (p<0.05). BDE-209 was the dominant congener identified in all samples (80%).

The result of the study shows that there is an association between occupational exposure and levels of PBDEs in blood, while higher levels of OH-PBDEs and MeO-PBDEs in the coastal population would be due to higher fish consumption.

Statistically, non parametric tests of association were used. Inclusion and exclusion criteria, together with bias control, are not described enough.

Yang Q. et al. (2013)²⁹ investigate levels of exposure to typical pollutants relates to e-waste dismantling and recycling processes, including PBDEs by measuring their concentrations in serum samples of a population (e-waste workers and local residents).

It is a cross-sectional study with two exposure groups and a control group. The first one was formed by 17 occupational exposed workers at a small dismantling workshops with rudimentary techniques. The second group included 18 local residents. The control group was formed by 21 people living 40 km away.

Participants were randomly recruited. Demographic information was obtained through questionnaire surveys.

Regarding the statistical analysis, concentration data of all the chemicals were logarithmically transformed to obtain normal distribution, confirmed by Kolmogorov-Smirnov test. Differences between groups were examined by independent-samples t-test. Multivariate linear regresion analysis was performed to exclude potencial confounding factors.

Serum levels of PBDEs of the exposure group were significantly higher (p<0.001) than those of the control group, but this was not the case for BDE-209 (p=0.83).

In the logistic regression test, the main positive correlation (p<0.05) shows that concentrations in serum in the exposed population was significantly higher than in the control group. No significant correlation was found between serum pollutants concentrations and age, BMI, years of working as e-waste worker and sampling season.

Living or working at e-waste recycling areas was associated to higher concentration of PBDEs in serum, except for BDE-209.

Discussion and conclusions

Epidemiologic information about the link between exposure to PBDEs in e-waste workers and the effect on human health is not very prolific.

The lack of coincidence among all the studies included in this review may be conditioned by the variability of the populations studied and the epidemiologic design used, since 16 out of the 20 studies have cross-sectional design, which limits our ability to assess temporality. Only two studies have a longitudinal design.

A major limitation is that only in four studies, population is randomly selected introducing a potential bias. In 14 studies, investigators did not adjust for the effects of confounders and no other possible exposure ways to PBDEs have been taken into account.

E-waste recycling process implies an exposure to many chemicals, so it is very difficult to assess the effects of the exposure to PBDEs separately.

We conclude that evidence is suggestive to infer association between serum PBDEs levels and working in e-waste recycling facilities. This evidence is consistent, with no studies showing different results, and it is repeated regardless the geographic area in which the study is carried out, although the magnitudes are different, ranging from 26 ng/g lipid in Sweden to 600 ng/g lipid in China, where the highest concentration is found (3436 ng g-1 l.w.),²⁷ which is probably due to the fact that in this study e-waste workers use very primitive techniques with very little protection measures, which would lead to a higher exposure. The level of evidence for this result, according to SIGN criteria is 3.

In eleven studies^{22-29,34,36,37}, high levels of PBDEs in serum were found among the population of e-waste surrounding areas and even in far away towns selected as control group. This result clearly indicates that general population without occupational exposure is somehow exposed to these chemicals. In any case, concentrations of PBDEs in e-waste recycling workers are still significantly higher than those in the control group. Two studies are coincident in this regard: Guiyu, China²³, PBDEs median levels in e-waste workers were 3.5 fold higher than those in population of a region located 50km away, and China^27, where the PBDEs total levels in blood in e-waste workers were 3.6 fold higher than in the population of a different Chinese town without PBDEs exposure known. The level of evidence, according to SIGN criteria was 3.

Concentration of PBDEs in blood is associated with exposure time, working procedures and protection measures (level of evidence 3). Age or BMI had no correlation.

An evidence was found (level 1-) about the efficiency of the improvement measures in industrial hygiene in order to reduce an exposure pathway to PBDEs on e-waste recycling activity^{28, 39.}

All the studies reviewed^19,30-33, investigating the connection between work exposure to PBDEs and levels of PBDEs in hair, showed that levels of PBDEs in hair in the exposed population were significantly higher than those in control population (level of evidence 3).

It is interesting, despite the fact that levels of PBDEs in hair in people living close to recycling areas were higher than in the people living in the cities, concentrations of PBDEs found in the dust collected from the houses closed to the recycling plants were lower than those found in the city houses. This suggest that PBDEs exposure in the reference population arises from sources such as diet and house dust ingestion⁴⁴.

While comparing levels of PBDEs in hair and dust, they observed that the proportion of deca- BDE decreases in expense of nona-BDE, compared to concentrations detected in dust, which suggest that metabólico debromination of BDE-209 into nona-BDE may occur.

Other studies^30-32,44 also report higher concentrations of PBDEs in hair in e-waste workers than in control groups. They are not identical each other depending on the technology used on e-waste dismantling, characteristics of the sample population and PBDEs pattern studied. In all reports, the major congener was BDE-209, which is approximately 97% of the deca-BDE mixture, which has been one of the most used in the last years.

Although BDE-209 has low bioavailability and short half-life (15 days), it was found that BDE-209 can be accumulated in human blood and milk. Higher brominated diphenyl ethers would be oxidatively metabolized into low brominated PBDEs, including penta- and nona-BDEs^23,27,44,45.

Biomonitoring not necessarily to identifies the source of PBDEs, since it may occur in places different than the workplace^19,46. Nevertheless, biomonitoring studies are useful to identify and characterize the exposure and show us the need of implementing exposure control measures²⁸.

It has been lately documented in laboratory studies that hydroxilated PBDEs (OH-PBDEs) and MeO-PBDEs produce thyroid toxicity⁴⁷ and disruption of ovarian steroidogenesis⁴⁸.

In studies in-vivo, OH-PBDEs have been detected in rats and mice blood after being exposed to mixtures of PBDEs o BDE-209^20,49. Nevertheless, in another in vitro study, OH-PBDEs were not detected after the exposure of human hepatocytes to BDE-209⁵¹.

In our review, we found several studies with level of evidence 3, which studies the presence of these metabolytes in workers serum. Levels of OH-PBDEs metabolytes^25,37 and MeO-PBDEs^24,25 were higher in the reference population than in e-waste workers.

Eguchi associates higher levels of MeO-PBDEs with marine fish intake. Yu³⁷ found OH-octa-BDEs and OH-nona- BDEs in serum samples from e-waste workers. In both studies, BDE-209 was the predominant congener in all the samples.

Nevertheless, Athanasiadou et al.²² studied child labour in Nicaragua dumps. Children in contact with e-waste showed higher levels of PBDEs and OH-PBDEs than children living 20km away. The major congener was BDE-47 and the less frequent BDE-209.

Yang²⁹ does not find significant differences in levels of BDE-209 among e-waste recycling workers and the control group. This suggests that there are diferentes pathways of exposur such as domestic, or low-brominated-BDE formed by debromination of BDE-209.

The highest concentrations in serum (octa- to nona- BDE) in e-waste workers compared with the reference population²⁵ would be explained by the BDE-209 debromination theory.

The measurement of the levels of octa- to nona-BDE and PBDEs metabolytes (OH and MeO-PBDEs) could be used to show long term work exposure, while the presence of BDE-209 would be used to assess recent exposure.

TSH is an important parameter of thyroid functions, because it may affect the levels of other hormones by acting on the hypothalamic hypophyseal axis.

Studies in rats show that a short-term exposure to some commercial PBDEs mixtures interfered with the thyroid hormone system via uridinediphosphate-glucuronosyltransferase (UGTs)^52,53.

Reported effects on TSH are not consistent. Wang H.³⁵ reports decreased concentrations associated with e-waste exposure. Nevertheless, Han G and Yuan^34,36 reports increased concentrations in the exposed population. Also, Han³⁴ found an association between levels of PBDEs and TSH concentrations.

Findings from several studies shows that free radicals released from PBDEs may cause irreversible oxidative damage in DNA molecules⁵⁴. It plays an important role in various diseases, such as pulmonary diseases, cardiovascular diseases and cancer^55,56.

The cytogenetic essay for micronucleus detection (CBMN: cytokinesis-block micronucleus) is a globally validated and technologically accessible study. It is useful to assess genetic inestability induced by genotoxic agents. Micronucleus are cytoplasmic bodies with nuclear nature that correspond to genetic material non properly incorporated to the daughter cells during cell division, they show chromosomic aberrations and have their origin in chromosomic breakages, in errors during replication or further DNA cell division and/or exposure to genotoxic agents.

In vitro studies^57,58 suggest that PBDEs may damage DNA, producing an increase in the number of micronucleated cells. In several studies³⁶, the authors found a higher presence of micronucleated cells in e-waste exposed population than in non-exposed population. This shows that PBDEs can be a genotoxic substance and that e-waste recycling workers may have a higher risk of diseases. In fact, the IARC (International Agency for Research on Cancer) classifies PBDEs as "possible carcinogenic substance".

8-Hidroxi-2´-deoxyguanosine (8-OHdG) is often used to asses oxidative damage⁵⁹. Results found in our review are not conclusive. Zhang G.F.³¹ reports that levels of 8-OHdG in urine after the workday were higher than at the beginning of it, showing a positive association between exposure to PBDEs and DNA oxydative damage.

Recent studies in human suggest that high levels of PBDEs in breast milk are related with cryptorchidism in newborns⁶⁰, low weight at birth and reduction in length and breast circumference in newborns⁶¹. It has been found a negative correlation between concentration of PBDEs in serum and the sperm count in young men⁶².

Results of studies are coincident, with a level of evidence 3. Noting an association between exposure to PBDEs in working women and the increase in levels of PBDEs in breastmilk and placenta.

One of the studies¹⁹ which analyzes levels of PBDEs in breast milk, placenta and hair samples from a group of childbearing-aged women working in a recycling site in order to relate them to possible health risk showed. Concentrations of PBDEs found in all samples were significantly higher in the exposure group than in non-exposed group.

This result matches with Tue N.M.'s study³⁸ in which levels of PBDEs in breast milk of women from three e-waste exposure areas (work exposure or not) were not higher than those found in urban area women.

In this study, BDE-209 was the predominant congener in the exposure group while BDE47 and BDE 153 were in the control group.

In Leung's study, the dominant congener in all samples was BDE 47. Levels of BDE-209 were not analyzed.

High body burden would not only cause problems in worker's health but also implies a potencial health risk in future generations. The estimate intake of PBDEs for a 6-month-old baby living in an e-waste area and being breastfed would be 572±839 ng/kg body wt/day, 57 times higher than in children in the reference area ¹⁹.

Studies in animals and in vitro show association between levels of PBDEs and adverse health effects.

The reviewed studies are coincident to establish an association between exposure to PBDEs and biological parameters alterations but due to the design of the reviewed studies, our ability to assess temporality of associations between exposure to PBDEs in e-waste workers and health effects is limited.

It seems reasonable to implement industrial hygiene measures to reduce levels of emission into the air and levels of exposure to PBDEs from recycling processes, also to implement personal and health protection measures.

Despite all efforts done during last years by different organizations, both in legislative tasks and in programs to determine adverse health effects of PBDEs, the focus is mainly environmental. Nevertheless, evolution in electronic market makes that e-waste represent an emergent work health problem. Further research should be conducted on epidemiologic studies on health impacts caused by e-waste recycling operations, that allow the establishment of causal relations. Regulatory and public health interventions must be developed and implemented to prevent and reduce PBDEs occupational exposure on e-waste workers.

Acknowledgements

The authors acknowledge gratefully the cooperation from Dr. Jerónimo Maqueda.

Correspondence:
Paula Lechuga Vázquez
Servicio de Prevención de Riesgos Laborales
Hospital Universitario Marqués de Valdecilla
Avda. Marqués de Valdecilla s/n
39008, Santander. Cantabria. Spain
E-mail: paulalechuga@hotmail.com

Recibido: 23-01-14
Aceptado: 17-07-14

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