Organophosphate esters and their specific metabolites in chicken eggs from across Australia: Occurrence, profile, and distribution between yolk and albumin fractions

Highlights

• Concentrations of OPEs and mOPEs in chicken eggs across Australia were measured.

• No spatial differences in OPEs or mOPEs concentrations were found in collected egg.

• Partitioning of OPEs/mOPEs between yolk and albumin was estimated for the first time.

• Yolk-albumin partitioning coefficient was negatively correlated to molecular mass.

• Metabolism of OPEs in liver may contribute to the accumulation of mOPEs in egg yolk.

Abstract

A substantial increase in the usage of organophosphate esters (OPEs) as flame retardants and plasticizers in rubbers, textiles, upholstered furniture, lacquers, plastics, building materials and electronic equipment has resulted in their increasing concentrations in the environment over time. However, little is known about the concentrations and fate of OPEs and their metabolites (mOPEs) in biota, including chicken eggs. The aim of this study was to understand the spatial variation in the concentrations in chicken eggs and the partitioning between yolk and albumin. In total, 153 chicken eggs were purchased across Australia and analysed for 9 OPEs and 11 mOPE. Most of the compounds were found to be deposited in egg yolk, where diphenyl phosphate (DPHP, 3.8 ng/g wet weight, median) and tris(2-chloroisopropyl) phosphate (TCIPP, 1.8 ng/g wet weight, median) were predominant mOPE and OPE, respectively. Moreover, no spatial differences in concentrations of OPEs and mOPEs in eggs purchased from different locations were found in this study. Although comparable levels of ∑OPEs were detected in egg yolk and albumin, much higher concentrations of ∑mOPEs were found in yolk than albumin. Meanwhile, a negative correlation (R² = 0.964, p = 0.018) was found between the molecular mass of analytes and partitioning coefficient of C_yolk/C_yolk+albumin (defined as chemical concentration in egg yolk divided by the sum of chemical concentrations in both yolk and albumin). These results indicate that n-octanol/water partition coefficients (log K_OW) may not be a crucial factor in the distribution of OPEs and mOPEs between egg yolk and albumin, which is important in understanding distribution of emerging organic contaminants in biota.

Introduction

Organophosphate esters (OPEs) have been widely used as flame retardants, plasticizers and anti-foaming agents, in furniture, textile, plastic, electronic equipment and construction materials (Marklund et al., 2003; Stapleton et al., 2011; Stapleton et al., 2012). Since the phase-out and regulations of some brominated flame retardants e.g. polybrominated diphenyl ethers (PBDEs), there has been a significant increase in production and consumption of OPEs as PBDE alternatives (Wei et al., 2015). The global consumption of OPEs was 500,000 tonnes in 2011 (Hou et al., 2016), and there demand was projected to increase to 685,000 tonnes in 2018 (Israel Chemicals Ltd, 2015).

OPEs are mainly used as additives, rather than chemically bonded to the products, and thus could be released from products via volatilization, abrasion and leaching during there service period (Marklund et al., 2005; Sundkvist et al., 2010). As a consequence, OPEs have been widely detected in environmental matrices such as water (Bollmann et al., 2012; Li et al., 2014), sediment (Cao et al., 2012; Yadav et al., 2018), air (Moller et al., 2012; Yadav et al., 2017; Okeme et al., 2018), dust (Abdallah and Covaci, 2014; Harrad et al., 2016; He et al., 2018b; Yadav et al., 2019) and limited biota samples, including eggs (Zheng et al., 2016; Hou et al., 2017; Briels et al., 2018; Briels et al., 2019; Poma et al., 2019).

While monitoring of OPEs in environmental compartments as above is important, it is even more important to monitor the levels of OPEs in food as it is directly related to human exposure to those chemicals. Eggs are thought to be a source of human exposure to persistent organic pollutants (POPs), particularly free range eggs that have been known for accumulating higher concentrations of contaminants such as dioxins (Schoeters and Hoogenboom, 2006). Yet, only a limited number of studies have been conducted on OPEs and related chemicals in chicken eggs (Rawn et al., 2011; Zheng et al., 2016; Poma et al., 2019).

In addition, our recent work (He et al., 2018b) found the co-existence of OPEs and there metabolites (mOPEs) in foodstuffs, including eggs in Australia. As mOPEs are the transformation products of OPEs, they have been used as biomarkers to assess human exposure to OPEs (Butt et al., 2014; He et al., 2018a; Meeker et al., 2013; Van den Eede et al., 2015a, b). However, the co-existence of OPEs and mOPEs in foodstuffs suggested direct exposure to mOPEs via diet, which may contribute to the observed mOPEs in humans. However, since this study was part of a total intake assessment covering many food items, the number of eggs analysed was very limited (n = 3), and the distribution between yolk and albumin was not reported since whole eggs were analysed (He et al., 2018b). The only other study analysing OPEs and mOPEs in eggs was specific on eagle eggs from North America (Stubbings et al., 2018). Moreover, different from the lipophilic flame retardants (e.g. PBDEs) that tend to accumulate in egg yolk, OPEs were also detected in albumin (Greaves and Letcher, 2014; Zheng et al., 2016). To our knowledge, no studies have assessed mOPEs in separated egg yolk and albumin. Therefore, no information is available on the distribution of mOPEs between the two fractions, which may provide some clues to not only the exposure to humans but also to the fate and behaviour of mOPEs in avian species.

This study thus aims to: 1) evaluate OPE and mOPE concentrations and there spatial variations in eggs, and differences in concentrations between free range and caged eggs; 2) investigate the partitioning of OPEs and mOPEs between yolk and albumin fractions; 3) estimate human exposure to OPEs and mOPEs from consuming chicken eggs.