Air quality monitoring is the main source of information for assessing the exposure of the population to ambient air pollution. Positive mutual correlations were significant among toluene, DMF, chloroform, and MEK in indoor, outdoor and personal exposure measurements. Benzene, ethylbenzene, m,p-xylene, and o-xylene were also mutually positively correlated in indoor, outdoor and personal exposure measurements. The high correlations between each other can be explained that the toxic pollutants could have come from the same source . However, the correlation relationship was not found between the two groups. It can be implied that the two group VOCs might be emitted from different kinds of pollutant sources.
The data from PRTR of the Korean pollutant emissions showed that most of toluene, DMF, MEK, and chloroform were emitted from DDIC. Outdoor and indoor concentrations of toluene, DMF, and chloroform in the exposed area were significantly higher than the concentrations in the controlled area both in summer and winter. Toluene and chloroform were widely utilized in dyeing, finishing processes and warranting examination, and were markers of gasoline vehicle emissions [10, 17]. Benzene was not utilized in dyeing and finishing processes, it has been known as markers of gasoline vehicle emissions . The concentrations of toluene, DMF, chloroform, and MEK in residential outdoor significantly decreased with increasing distances from DDIC. Conversely, the concentration of outdoor benzene was found to increase with distances increased from DDIC. Therefore, it may be suggested that toluene, DMF, chloroform, and MEK in the ambient air of the exposed area were mainly emitted from DDIC.
Benzene, ethylbenzene, m,p-xylenes, and o-xylenes were the major VOCs for mobile sources in the urban air . The previous study also suggested that these compounds could have originated from the use of solvents and evaporative losses of fuel . Several studies suggested that good correlations among benzene, toluene, ethylbenzene, and xylene from traffic emissions were r = 0.79–0.92 (p < 0.01) [21,22,23]. However, poor correlations of benzene, toluene, ethylbenzene, and xylene were observed (r = 0.14 ~ 0.76) in this study. This can be explained by the ethylbenzene and xylene that could have come from industrial solvents and traffic emissions, while benzene mainly came from traffic sources. The poor correlation could be also explained by the mixed sources of ethylbenzene and xylene in the exposed area.
The indoor, outdoor and personal exposure concentrations of toluene, DMF and chloroform in the exposed area were also significantly higher than the corresponding concentrations in the controlled area in summer and autumn. Positive mutual correlations were significant among toluene, DMF, chloroform, and MEK in indoor, outdoor and personal measuring. Benzene, ethylbenzene, m,p-xylene, and o-xylene were also mutually positively correlated in indoor, outdoor and personal measurements. The indoor and personal concentrations were all in accordance with the outdoor situations. Residential indoor sources, such as cooking, cigarette smoking, materials used on the wall flooring and furniture, could be major contributors to the indoor concentrations of VOCs. However, it can be suggested that the personal and indoor concentrations of selected VOCs were also obviously affected by outdoor pollutant sources in exposed area in DDIC. Personal exposure concentrations of VOCs were also affected by many factors including time-activity patterns. Even so, outdoor pollutant sources from DDIC affected the indoor air quality and personal exposure in the exposed area. Since VOCs easily evaporate or sublimate into the air at normal room temperature, they can migrate from a source and enter buildings nearby to a dangerous level . It also differentiates the pollution amount of indoors by distances from emission sources .
Cancer risk for chloroform in the exposed area was greater than in the controlled area and even greater than 10− 4. HQ of toluene, DMF, and MEK in the exposed area were much higher than in the controlled area. Morbidities of respiratory diseases, anaphylactic diseases and cardiovascular diseases in the exposed area were significantly higher than in the controlled area. It also suggested that the health of residents living near DDIC could be affected by pollutants emitted from DDIC. The results suggested a need for environmental policies to reduce pollution and the DDIC residents exposure. The health assessment studies identified self-reported symptoms of asthma in both adults and children as a significant finding. It is appropriate for this health risk assessment to consider the mixture effects of the pollutants that are recognized respiratory irritants which are high enough in concentrations. The morbidities of asthma and other respiratory diseases in the exposed area were significantly higher than in the controlled area. The area nearby is a dense conglomerate of industry and human settlement. Special attention should be given to communities located in the areas close to DDIC.
Some VOCs concentrations such as toluene and MEK were higher in autumn than in summer. Concentrations in different seasons could be influenced by many factors, such as source variation, fuel consumptions, climatic conditions, and chemical reaction. Daegu has a continental climate with dry winters and hot summers. The area receives little precipitation except during the rainy season of summer. The data from Korea Meteorological Administration showed the average precipitation which varies from 224.0 mm to 235.9 mm between July and August (summer). On the contrary, the average precipitation varies from 33.8 mm to 30.5 mm between October and November (autumn). Average precipitation days (≥ 0.1 mm) varies from 14.4 days to 12.8 days between July and August, however, average precipitation days (≥ 0.1 mm) are approximately 5 days. The meteorological conditions make VOCs difficult to regional physical dispersion/ transportations and deposition. Another factor, that could have affected the concentration of VOCs in the summer, is dilution due to the increase in the mixing height . Although the high temperature during summer will help the evaporation of VOCs, as they decay quickly by chemical removal reaction rates. Over the course of a year, the temperature of Daegu typically varies from − 5 °C to 32 °C. The daily mean temperature was 9.0 °C, and the average low temperature was 4.2 °C which is in November. After the middle of November, the indoor heating could have also contributed to the high concentrations of VOCs in autumn owing to fuel consumptions.
According to the study of Jo et al. (2004), the geometric mean concentration of toluene, benzene, m,p-xylene and o-xylene was 255 μg/m3, 7.2 μg/m3, 7.7 μg/m3 and 4.3 μg/m3 in outdoor for areas which are 100 m from the boundary of the DDIC, respectively, which was conducted between 10 October and 21 December 2000. As to the outdoor for areas between 500 m and 800 m away, the geometric concentration of toluene, benzene, m,p-xylene and o-xylene was 55.5 μg/m3, 10.5 μg/m3, 11.2 μg/m3 and 7.2 μg/m3, respectively . In this study, the contemporaneous arithmetic mean value of toluene, benzene, m,p-xylene, and o-xylene was 161.37 μg/m3, 3.54 μg/m3, 10.48 μg/m3 and 1.73 μg/m3, respectively.
It was found out that VOCs can be emitted from many anthropogenic sources in urban and industrial areas, such as industrial processes and vehicle exhaust. Due to the obvious impacts on environments and human health, many studies suggested VOCs should be controlled for better regional air quality. However, there are few studies about specific industry VOC emission and impacts on the ambient environment [21, 27]. This study provided the detailed information about the ambient air concentrations of VOCs in nearby dyeing industry. Compared to similar studies, using a considerable large samples is the main strength of this study. Moreover, indoor, outdoor and personal exposure concentrations were measured both in the exposed area and the controlled area simultaneously, something that is rarely done in other studies.
The limitations of this study might be the possible confounding factors such as the distance from highly trafficked roads and indirect smoking. It was reported by 19.68% of volunteers in the exposed area and 10% in the controlled area that there were more than 6 lanes of roads within 500 m of their houses. And according to the study of Park et al. (2014), the concentrations of benzene, m,p-xylene, and o-xylene were influenced by exposure to second-hand smoke . The data from the questionnaire showed that the rate of volunteers living with smokers was 13.98% and 12.98% in exposed area and the controlled area, respectively. The smoking of public places are forbidden in South Korea. Most participants responded that those living together did not smoke in the house indoors.