Current situation of workers’ health in some plastic production facilities using Styrene

People may be exposed to styrene through three main routes: through the digestive tract, through breathing air, and through the skin. The most common exposure of workers to styrene is through inhalation. Exposure to styrene through the skin and eyes is less common, especially through the digestive tract, which is rare.

Exposure to styrene causes irritation of the mucous membranes of the eyes, nose, throat and respiratory tract. Chronic exposure to styrene over a long period of time can cause polyneuritis, sensory disturbances, hearing loss, memory impairment, cardiac arrhythmias, impaired liver function, etc. Exposure to large quantities can lead to the onset of “styrene sickness” with signs such as headache, nausea, vomiting, muscle weakness, fatigue, dizziness, movement disorders, etc.

This article refers to the current state of health and disease structure in workers in some plastic production facilities using styrene, as part of the research results of the project “Study on the current status of styrene poisoning and the proposal to add to the list of occupational diseases insured in Vietnam” which presided by the Vietnam National Institute of Occupational Safety and Health.

1. Characteristics of research subjects

The study was carried out on 899 workers at 6 plastic production facilities in the North and the South, including 239 male workers and 660 female workers:

Distribution of labor by gender: Female workers account for a higher proportion than male workers (73.4% and 26.6% respectively) and there is a difference (p < 0.05).

Average age and working age by gender: The average age is 39 ± 9 years (from 17 to 75 years). The average working age is 5 ± 4 years (from 1 to 30 years).

2. Physical status and general health classification

Average weight and height of workers: The average weight of both genders is 55.2 ± 8.5 kg. In which, the weight of male workers is 59.5 ± 9.6 kg and female workers is 53.6 ± 7.5 kg. The average height of male workers is 163.1 ± 7.1 cm and female workers is 155.9 ± 6.3 cm.

General health classification: Workers in plastic production facilities have health classification of categories I and II accounted for 50.2%, the rate of category III is 48.1%, the rate of category IV is 1.8%. The health classification data of category I in this study is relatively modest, accounting for only 1.3%, in which females are more than males.

3. Situation of common diseases

BMI: The average body mass index (BMI) (22.1 ± 2.7 kg/m2) is generally within the normal range. In which, BMI for men is 22.3 ± 2.9 kg/m2 and for women is 22.0 ± 2.6 kg/m2. There was no difference in BMI between men and women (p > 0.05).

Results of classification of BMI according to WHO (World Health Organization, 2000) show that: Subjects are defined as chronic energy deficiency (CED) when body mass index BMI < 18.5kg/m2. The results in this study showed that the overall CED rate was 6.0%. When analyzing CED separately by gender, the CED results in males (8.8%) were higher than those in females (5.0%). The overall prevalence of overweight and obesity in this study was 13.2%, of which the rate of overweight and obesity in men (19.2%) was also higher than that of women (11.1%).

Prevalence of diseases through clinical examination: Workers in plastic production facilities have the highest rate of diseases: Dentomaxillofacial diseases (62.5%), followed by eye diseases (50.1%) ), otorhinolaryngological diseases, mainly upper respiratory tract infections (48.2%) and internal diseases (38.8%). The prevalence of internal and eye diseases was related to age and occupational age (p < 0.05), but there was no difference between men and women (p > 0.05). The prevalence of high blood pressure in men (10.1%) was higher than that of women (3.4%), the difference was statistically significant (p < 0.05). Dermatological diseases (mainly eczema, fungi and allergies) accounted for 7.0%, of which 23.8% had contact dermatitis and all were in the group of people directly working in high risk positions (product molding, mixing raw materials). There is no difference in incidence between genders, age and occupation (p > 0.05).

4. Work-related disease symptoms

Hearing loss: The percentage of workers with general hearing loss is 15.0%. Comparing between men and women, the percentage of workers with hearing loss is higher in men (24.9%) than in women (9.8%), the difference is statistically significant (p < 0.01). Environmental measurement results show that most of the noise measured at the working positions are below the allowable standard (≤ 85dB). The incidence of hearing loss in one ear and in both ears is similar. The prevalence of bilateral hearing loss in men is higher than that of women and vice versa, the rate of unilateral hearing loss in women is higher than in men and the difference is statistically significant (p < 0.05). In addition, the rate of hearing loss tends to increase with age and is highly concentrated in the group with working seniority < 5 years, but there is no significant difference (p > 0.05).

Respiratory function impairment: The prevalence of ventilation disorders in subjects with respiratory function impairment showed a decline in respiratory function of 30.9%. In general, the prevalence of female respiratory function impairment is higher (32.5%) than that of male (27.8%), however, the difference is not statistically significant (p > 0.05).

Clinical test results:

Glutamic Oxaloacetic Transaminase (GOT) test: The average rate of elevated liver enzymes in workers is 8.5%. Comparing between the two groups, the percentage of workers with elevated liver enzymes in men (17.2%) was higher than the percentage of women with elevated liver enzymes (4.1%) with (p < 0.01). This ratio is not related to the age and occupation of the workers (p > 0.05).

Hemoglobin (Hgb) blood test: The average rate of anemia in workers is 10.6% and at the level that should be warned as recommended by the World Health Organization (5-19%). The rate of anemia in women (15.0%) was much higher than that in men (1.3%) with (p < 0.01). Anemia in women is a matter of great concern because it is related to the menstrual cycle and reproductive health problems of female workers.

MA and PGA metabolite test in urine: Test results for styrene in blood and styrene’s MA and PGA metabolites in urine showed that 28.8% showed no MA + PGA concentration. The proportion of testers with quantifiable total MA + PGA concentrations is 70.7%. The number of subjects with urinary MA + PGA concentration higher than the allowable standard accounted for 2.5% (equivalent to 22 people) (400mg/g creatinine – according to ACGIH, 2018), of which there were subjects exceeding 3-4 times higher than the allowable standard.

In addition, out of 22 people with MA + PGA levels above the threshold, all had blood styrene levels (> 1mg/l), while the results of measuring styrene levels in the air environment of the workplace at the surveyed locations (the area of ​​the molding machine, the mixing of raw materials, etc.) are very low and below the allowable threshold. This shows that there is styrene exposure in workers at the surveyed facilities even when the concentration of styrene in the air environment is very low.

Conclusion

Our study was carried out on 899 workers, including 239 (26.6%) male workers and 660 (73.6%) female workers. The average age is 39 ± 9 years. Average working age is 5 ± 4 years. Workers in general both showed signs of chronic energy deficiency and significant signs of obesity in both groups. The labor group has a high rate of internal diseases, otorhinolaryngological diseases and eye diseases, especially dentomaxillofacial diseases. Anemia accounted for 10.5% and high liver enzymes accounted for 8.5%. General health classification focusing on category II and III.

Occupational diseases: Among 7.0% have dermatological diseases, of which 23.8% of these have contact dermatitis and all are in the contact group; there are signs of hearing loss (15.0%) and respiratory function impairment (30.9%) in which restrictive ventilation disorders account for a high proportion.

There were 2.47% (22 subjects) with high MA + PGA concentration exceeding the allowable standard, of which 3 workers had 3-4 times higher than the allowable standard and 18/22 workers had styrene levels in their blood.

With the above-mentioned scientific bases, it is necessary to have research to develop standards for diagnosis and assessment of occupational styrene poisoning in the context of Vietnam, when the ILO and many countries in the world have recognized it.

Dr. Vu Xuan Trung; Dr. Pham Thi Bich Ngan; Dr. Nguyen Thi Hien

(Source: Vnniosh.vn)