Short-chain chlorinated paraffins in cooking oil and related products from China

Highlights

• SCCPs were detected in cooking oil, fried food, and raw seeds from Chinese cities.

• Cooking oil contained SCCP concentrations of <9–7500 ng g⁻¹.

• Estimated total SCCP intake in cooking oil for a Chinese person was <0.78–38 μg d⁻¹.

• Cooking oil and fried food could be the sources of SCCPs to Chinese people.

Abstract

Short-chain chlorinated paraffins (SCCPs) are emerging persistent organic pollutants. It has been found that dietary intakes of SCCPs in China have recently increased and are now higher than in Japan and Korea. The contribution of cooking oil to dietary exposure to SCCPs in China was evaluated by analyzing SCCPs in cooking oil, raw seeds used to produce cooking oil, and fried confectionery products collected in China in 2010 and 2012. Detectable amounts of SCCP homologs were found in 48 out of the 49 cooking oil samples analyzed, and the SCCP concentrations varied widely, from <9 to 7500 ng g⁻¹. Estimated dietary intakes of total SCCPs in cooking oil ranged from <0.78 to 38 μg d⁻¹. The estimated dietary intake of SCCPs was relatively high (mean 14.8 μg d⁻¹) for residents of Beijing. Fried confectionery was found to contain SCCP concentrations of 11–1000 ng g⁻¹. Cooking oil might therefore be one of the sources of SCCPs to Chinese diets. SCCPs were also detected in raw seeds used to produce cooking oil, but the concentrations varied widely. The SCCP homolog patterns in the raw seed and cooking oil samples were different, implying that the seeds used to produce the oil (and therefore the soil on which the seeds were produced) were unlikely to be the sources of SCCPs in cooking oil. Further investigations are needed to determine the routes through which cooking oil becomes contaminated with SCCPs during the production and processing of the oil.

Introduction

Chlorinated paraffins (CPs) are used in a wide range of industrial applications including in plasticizers, flame retardants, cutting fluids, and lubricants (European Chemicals Bureau, 2008). The CPs are typically categorized into three groups according to the lengths of the carbon chains, and these groups are short-chain CPs (SCCPs, with C_10–13 components), medium-chain CPs (C_14–17), and long-chain CPs (C_18–30.). SCCPs appear to be persistent in the environment and have the potential to strongly accumulate in biota (Persistent Organic Pollutants Review Committee, 2010, Fisk et al., 1996, Fisk et al., 1998, Houde et al., 2008, Iozza et al., 2008). The International Agency for Research on Cancer has classed SCCPs as group 2B compounds (International Agency for Research on Cancer, 1990), and SCCPs are also classified as Carc. 2 in Annex VI of Regulation (EC) NO. 1272/2008 in European Union (EU), possibly carcinogenic to humans (EC, 2008). Recently, Geng et al. (2015) found that SCCPs can stimulate β-oxidation, and SCCPs are therefore considered to be peroxisome proliferators. SCCPs are currently under review as candidates for inclusion in the Stockholm Convention list of persistent organic pollutants (Persistent Organic Pollutants Review Committee, 2010).

CPs have been produced around the world. Notably, the total amount of CPs produced in China has continually increased in recent years, 1,000,000 t being produced in China in 2009 (Chen et al., 2011, Tong et al., 2009). Three of the commercial CP formulations are called CP-42, CP-52, and CP-70, and they have chlorine contents of 42%, 52%, and 70%, respectively. More than 80% of the total amount of CPs produced in China in 2008 was of CP-42 and CP-52, which are used as plasticizers in poly(vinyl chloride) (China Chemical Reporter, 2004, China Chemical Reporter, 2009). CP-42 and CP-52 contain SCCPs but also contain CPs with longer carbon chain lengths that are classified as medium- and long-chain chlorinated paraffins (Yuan et al., 2010).

The release of SCCPs can occur during the production, storage, transportation, use, disposal, and recycling of CP-containing products (Persistent Organic Pollutants Review Committee, 2010). Most SCCP emissions probably occur during the formulation and manufacture of products containing SCCPs (de Boer, 2010). The release of SCCPs into sewers has been found to result in SCCPs accumulating in sewage sludge (Zeng et al., 2012a, Zeng et al., 2012b) and the aquatic environment (Gao et al., 2012, Tomy et al., 1997). It has also been suggested that SCCPs enter the environment through evaporation and are transported in the vapor phase, because SCCPs have been found in air samples collected at remote sites (Li et al., 2012), soil in remote non-industrial areas such as Chongming Island, China (Wang et al., 2013a), and even in marine mammals in the Arctic (Tomy et al., 2000). SCCPs have been detected in bivalves (Yuan et al., 2012), fish (Ma et al., 2014a, Reth et al., 2005), birds (Reth et al., 2006), and human milk (Thomas et al., 2006), so it has been concluded that biota can be exposed to SCCPs through the food chain and that SCCPs can bioaccumulate.

In a previous investigation (Harada et al., 2011) we found that the dietary exposure of residents of Beijing to SCCPs (geometric mean 620 ng (kg body weight)⁻¹ d⁻¹ in 2009) increased by two orders of magnitude between 1993 and 2009. This finding raised questions about the food items that contributed most to SCCP intakes in Beijing. The consumption of fish is considered to be a major source of lipophilic pollutants to humans (Feo et al., 2009, Ma et al., 2014a, Yuan et al., 2012, Zeng et al., 2011b). Oils and fats could also be important dietary sources of SCCPs because the estimated log K_ow values of CPs show that CPs will partition strongly into lipophilic matrices (Hilger et al., 2011). Out of 11 types of food from Japan that were analyzed for SCCPs, the SCCP concentrations were highest in the oil and fat samples (Iino et al., 2005). A feature of Chinese food culture is that a great deal of cooking oil is used for stir-frying and deep frying. Because of this, and its large population (nearly 1.4 billion people), China probably has one of the world’s largest markets for oil seeds and cooking oil. Chinese people, especially northern Chinese people, often consume ready-prepared fried food, such as fried dough sticks and twists, fried vegetable balls, fried peanuts, and fried chicken, as a snack or as part of a meal. Cooking oil and fried confectionery are consumed in relatively large amounts in almost all parts of China, and an average per capita oil and fat consumption of 32.7 g d⁻¹ has been reported for Chinese people (Ministry of Public Health of China, 2004). Furthermore, it has been reported that recycled cooking oil called “gutter oil” has been on the market in China and actually is assumed to be used by small restaurants and street food vendors (BBC News, 2011). We supposed that there could be a possibility of contamination by gutter oil in some cooking oil which may show a unique SCCP homolog profiles.

In the study presented here, we assessed the exposure of Chinese people to SCCPs in food. There were two specific aims of the study. First, we aimed to evaluate the contribution of SCCPs in oil and fat to the total dietary exposure to SCCPs of people in different parts of China. To achieve this we analyzed SCCPs in cooking oil and fried confectionery products collected in China in 2010 and 2012. Second, we aimed to estimate the importance of different sources of SCCPs to cooking oil. SCCPs in cooking oil can originate in the raw vegetables or seeds used to produce the oil or can enter the oil during the production process if inappropriate procedures (such as gutter oil) are used.