Occurrence and fate of organophosphorus flame retardants and plasticizers in coastal and marine surface waters

Abstract

This comprehensive study focused on the spatial and seasonal variations of organophosphorus flame retardants and plasticizers (OPs) in surface water from the estuary of the River Elbe and the German Bight (North Sea). 100 surface water samples were extracted by solid phase extraction (SPE) and analyzed by gas chromatography–mass spectrometry (GC–MS) with regard to 16 different OPs. The dominating substance was found to be tris(1-chloro-2-propyl) phosphate (TCPP) (Elbe: 40–250 ng L⁻¹, German Bight: 3–28 ng L⁻¹). Furthermore, triethyl phosphate (TEP), tri-iso-butyl phosphate (TiBP), tris(2-butoxyethyl) phosphate (TBEP), and triphenylphosphine oxide (TPPO) were detected in concentrations up to 180 ng L⁻¹. Seasonal trends were detected for the longitudinal profile of the Elbe estuary. Besides the dilution of river water with North Sea water toward the mouth, leading to decreasing concentrations at the four sampling cruises (March, May, August, and October, 2010), an additional depletion of non-halogenated OPs was observed in summer which is supposed to be due to biodegradation or photodegradation.

In addition, a comparison of all important tributaries of the German Bight (Elbe, Ems, and Weser) as well as the indirect tributaries Meuse, Rhine, and Scheldt was done by multivariate statistical methods. It could be shown that the contribution of non-halogenated alkylated OPs in the Rhine was higher than in all other tributaries. The riverine input of OPs into the North Sea via the investigated tributaries was estimated to be about 50 t yr⁻¹.

Introduction

Flame retardants and plasticizers based on organophosphorus acid esters (OPs) are a widely used substance group. Varying alkyl- and aryl-ester groups, some of them halogenated, lead to a large variation of their physico-chemical properties – ranging from very polar and volatile (e.g. trimethyl phosphate) to non-polar and non-volatile (e.g. tri(ethylhexyl) phosphate) (Reemtsma et al., 2008, SRC PhysProp Database Demo, 2010). This makes them useful for various different applications from flame retardants in polyurethane foam (especially the halogenated OPs) and plasticizers in flexible PVC (primarily non-halogenated OPs) to some minor applications as additives in computer housings or hydraulic fluids. A good overview of the usage of different OPs is given by Marklund et al. (2003).

The worldwide usage of OPs was 207,200 t in 2004 (EFRA, 2010) and especially due to the replacement of the banned polybrominated diphenylethers (PBDEs) by OPs an increasing trend can be noticed (Stapleton et al., 2009). Already in the late 1970s first studies on the occurrence and fate of OPs in the aquatic environment were published (Sheldon and Hites, 1978, Saeger et al., 1979). Due to the fact that the emissions into the environment are still increasing, the OPs can be classified as “re-emerging pollutants” (Reemtsma et al., 2008).

Since OPs are not chemically bonded to the polymeric materials, they can undergo diffusion processes and be emitted into the environment. By the reason of the large variation in physical–chemical properties, OPs can be transported in different environmental media and have been detected in various environmental compartments. High concentrations up to a few μg m⁻³ were detected in indoor environments (Tollbäck et al., 2010) whereas in outdoor air concentrations of a few ng m⁻³ were measured (Saito et al., 2007, Möller et al., 2011). Surface water concentrations ranged between a few ng L⁻¹ up to a few hundred ng L⁻¹ (Andresen et al., 2004, Regnery and Püttmann, 2010). Especially the halogenated OPs are supposed to be highly persistent in the environment and only slightly biodegradable. Due to this they are insufficient degraded in sewage treatment plants and enter the aquatic environment (Andresen et al., 2004, Marklund et al., 2005). Several OPs are known to be toxic (e.g. neurotoxic or carcinogen) and additionally, the lipophilic OPs have the potential to bioaccumulate (Reemtsma et al., 2008).

This is the first comprehensive study of organophosphorus acid triesters (OPs) in the estuaries of all important tributaries of the German Bight (North Sea), i.e. the rivers Elbe, Weser, and Ems, as well as the indirect tributaries Meuse, Rhine and Scheldt, and the German Bight (North Sea) itself. Within this sampling region, OPs were analyzed in order to determine possible seasonal trends, and to compare the substance patterns of the different tributaries using multivariate statistical methods. Finally, the riverine input of OPs into the German Bight (North Sea) was estimated. This study covered 16 different OPs; thereunder three chlorinated alkyl phosphates (tris(2-choroethyl) phosphate, TCEP; tris(1-chloro-2-propyl) phosphate, TCPP; tris(dichloroisopropyl) phosphate, TDCPP), ten non-halogenated alkyl phosphates (trimethyl phosphate, TMP; triethyl phosphate, TEP; tri-n-propyl phosphate, TPrP; tri-iso-propyl phosphate, TiPrP; tri-n-butyl phosphate, TBP; tri-iso-butyl phosphate, TiBP; tripentyl phosphate, TPeP; trihexyl phosphate, THP, tris(2-ethylhexyl) phosphate, TEHP; tris(2-butoxyethyl) phosphate, TBEP), two aryl phosphates (triphenyl phosphate, TPhP; tricresyl phosphate, TCP), and also the synthetic intermediate triphenylphosphine oxide (TPPO). A list of the OPs analyzed in this study with their chemical structures, applications, and physico-chemical properties is given in Table S1 of the supplementary material.