Seasonal variations and inhalation risk assessment of short-chain chlorinated paraffins in PM_2.5 of Jinan, China

Highlights

• Seasonal variation of SCCPs in Jinan PM_2.5 with winter maximum and summer minimum.

• SCCPs concentrations had significant positive relationship with PM_2.5

• C₁₀ congeners and Cl₇ congeners predominated in PM_2.5 samples.

• SCCPs exposure via inhalation poses no significant risk for human health in Jinan.

Abstract

Short-chain chlorinated paraffins (SCCPs) were added to the Stockholm Convention on Persistent Organic Pollutants (POPs) at the eighth meeting of the conference of the parties in 2017. As a consequence, increasing environmental attention and international regulation on SCCPs is expected in the future. Inhalation uptake of particulate matter (PM) was an important exposure pathway for POPs into the human body. In the present study, a total of eighty PM_2.5 samples were collected in the four seasons of the year at an urban site (Shandong University, Jinan) in Shandong province to investigate the seasonal changes of SCCPs and their inhalation exposure risks to human health. The concentrations of SCCPs ranged from 9.80 to 105 ng m⁻³, with the mean value of 38.7 ng m⁻³. The highest concentrations of SCCPs were detected in winter, while the lowest concentrations were in summer. SCCPs concentrations were positively correlated with the mass concentrations of PM_2.5 (r = 0.629, p < 0.01), and negatively correlated with the ambient temperature (r = −0.447, p < 0.01). The SCCPs congeners with 10 carbon atoms (C₁₀ congeners) and 7 chlorine numbers (Cl₇ congeners) were the predominant congeners, which contributed 35% and 37% of the total SCCPs contamination, respectively. The average inhalation exposure was estimated to be 1.75 × 10⁻⁴ mg kg⁻¹ day⁻¹ for adults, which is much lower than the “no observed adverse effect level” (NOAEL) of 100 mg kg⁻¹ day⁻¹ given by European risk assessment for SCCPs.

Introduction

Chlorinated paraffins (CPs), also known as polychlorinated n-alkanes (PCAs), are complex mixtures produced by direct radical chlorination of n-alkane feedstocks (Bayen et al., 2006). CPs were widely used in commercial products, such as plasticizers, flame retardants, paints, lubricants in metal working fluids, and fat liquoring of leather (De Boer et al., 2010). According to the length of carbon chain, CPs are generally classified into short-chain CPs (SCCPs, C₁₀₋₁₃), medium-chain CPs (MCCPs, C₁₄₋₁₇), and long-chain CPs (LCCPs, C ≥ 18) (Feo et al., 2009). SCCPs are believed to be much more toxic to aquatic life than the related MCCPs or LCCPs, which can lead to adverse effects on the thyroid hormone system, liver, and kidneys with long-term environmental exposure (UNEP, 2016). Thus, SCCPs have gained considerable international attention and have been currently listed in Annex A in the Stockholm Convention on Persistent Organic Pollutants (POPs) at the eighth meeting of the Conference of the Parties in 2017 (UNEP, 2017). SCCPs have been ubiquitously found in the environment matrices of industrialized regions and even in polar regions (Du et al., 2018; Li et al., 2017; Li et al., 2016; van Mourik et al., 2016; Wei et al., 2016). Therefore, it is very necessary to assess the ecological risks of SCCPs in the environment.

The worldwide CPs production started in the 1930s, and China began the CPs production at the end of 1950s (De Boer et al., 2010). In 1980s, the CPs production in China increased rapidly because of the large demand of plasticizer in the plastics industry (De Boer et al., 2010). In 2013, CP production reached 1.05 million tons in China (accounting for 15% of the global CP production), making China one of the largest producers, exporters, and consumers of CPs (Zhang et al., 2017). However, due to the technical problems in the production process, there are no specified chain lengths in the plant produces (Wu et al., 2013). Diverse number of carbon atoms and different degree of chlorination result in various physical-chemical properties of CPs, which leading to the wide application in the commercial products and processes (De Boer et al., 2010). Anthropogenic releases of SCCPs into the environment may occur during production, transportation, storage, usage of SCCPs containing products, disposal and burning of waste and landfilling of products (Fiedler, 2010). If released as dust from these operations, the SCCPs would be adsorbed to particulate matters because of their high octanol–air partition coefficients and sorption property (Wang et al., 2012).

Recently, the working group of International Agency for Research on Cancer (IARC) has classified the particulate matter (PM) from outdoor air pollution as carcinogenic to humans in the epidemiological study (IARC Group 1) (Loomis et al., 2013). Along with PM, the pollutants (including organic pollutants, inorganic pollutants and other contaminants) adsorbed on the PM may cause serious respiratory infections and other diseases (Hassanvand et al., 2015). PM_2.5 is the particulate matter with an aerodynamic diameter equal or <2.5 μm, which are believed to be easily respired into the deep portions of lung, producing a great health risk to humans (Brauer et al., 2012). PM_2.5 is increasingly used as the indicator of air pollution all over the world, and their levels are high in some rapidly industrialising countries, notably in Asia (Loomis et al., 2013). Huang et al. investigated the particle size dependent distributions of SCCPs in PM fractions, and found that SCCPs are mainly associated with PM_2.5 samples in both outdoor and indoor air (Huang et al., 2017). Gas-particle fractionations of SCCPs were investigated in previous studies, the average fraction of total SCCPs in the particle phase was 67% in the winter but this dropped significantly to 6% during summertime (Wang et al., 2012). Zhu et al. reported that the average fraction of total SCCPs in particulate phase was 63% in winter and 3% in summer (Zhu et al., 2017). In UK atmosphere, the average percentages of SCCPs in the particulate phases was 9% in the period April to May (Barber et al., 2005) and 4.3% (range 1.4–5.1%) in May (Peters et al., 2000). To date, continuous investigations on SCCPs levels in PM_2.5 and their inhalation risk assessment in the four seasons were scarce.

PM_2.5 has small particle size, large surface area, strong activity, long residence time in the air and could be transported to remote areas through long-range atmospheric transport. PM_2.5 accompanied with toxic substances has an adverse impact on the atmospheric environmental quality and human health. Jinan is the capital city of Shandong province with high population density and is also one of the most heavily polluted cities in China (Cheng et al., 2011). Therefore, concern on SCCPs in the PM_2.5 from Jinan should be given enough attention. This study collected PM_2.5 samples in the four seasons of the year, aiming at: 1) monitoring the seasonal distribution of SCCPs levels and congener profiles in the PM_2.5 of Jinan; 2) investigating the influence factors which affected the occurrence of SCCPs in the outdoor environment; 3) evaluating the human exposure to SCCPs due to inhalation of PM_2.5 in heavily populated and industrialize cities.