Fate of Chlorinated Flame Retardants in the Environment and Water Treatment Jörg E. Drewes, Christiane Hoppe, Christopher L. Bellona, and Gary Wang Colorado School of Mines, Environmental Science and Engineering Division Golden, CO 80401-1887, U.S.A.

Abstract Recent studies have confirmed the occurrence of chlorinated flame retardants in wastewater, wastewater impacted streams and ground water under the impact of surface water. Several studies point to a very unique and persistent behavior of these compounds in the environment and TCEP, TCPP and TCDPP can essentially be found in any treated wastewater sample of source water under the impact of wastewater discharge. This study examined the occurrence, transport and fate of chlorinated flame retardants in the environment as well as engineered systems (i.e., processes employed during wastewater and drinking water treatment) and addresses their potential adverse effects on aquatic life and human health. This study builds upon experiences gathered through monitoring studies of conventional and advanced wastewater treatment facilities (e.g., activated sludge treatment, membrane bioreactors) and drinking water facilities (e.g., coagulation/flocculation, activated carbon, disinfection, advanced oxidation, highpressure membranes) as well as natural systems (e.g., soil-aquifer treatment, riverbank filtration).

Introduction Flame retardants are used in a wide variety of materials and applications. They can either be incorporated into various materials, such as structural plastics, foams, textile fibers, impregnated into timber or textile yarns, or can be added to protective coatings (ERFA 2006). Flame retardants can be classified in the following chemical families: inorganic chemicals (including antimony, aluminum and tin compounds), bromine and chlorine based flame retardants, organophosphorus compounds, and nitrogen based flame retardants. Chlorinated phosphate esters belong to the group of organophosphorus compounds, which had a market share of 58,000metric tons in the United States in 2001 with a worldwide consumption of 186,000tons (ERFA 2006). Triphosphates are esters of phosphoric acid, whereby the hydrogen atoms of the hydroxy groups are each replaced by an organic moiety of the same structure, hence the term “tris” (NICNAS 2001). These moieties may be either aliphatic or aromatic. Halogenated alkyl-phosphate esters are manufactured by the reaction of alkylene oxides and phosphorus chlorides in the presence of catalysts. Commonly used aliphatic chlorinated trisphosphates are tris(2-chloroethyl)phosphate (TCEP), tris(1-chloro-2-propyl)phosphate (TCPP), and tris(1,3-dichlor-2propyl)phosphate (TDCPP). The physicochemical properties of these flame retardants are summarized in Table 1. All three compounds are appreciably soluble in water, with TCEP having the highest solubility of 8 g/ L (Table 1). Chlorinated alkyl-phosphate esters are used globally as flame retardants in both rigid and flexible polyurethane foam (EFRA 2006). A major application of halogenated

phosphate ester flame retardants is the reduction of flammability in flexible foam used in domestic, public and automotive applications, i.e, upholstered furniture, mattresses, car interiors, etc. They are also used in rigid foam for thermal insulation to meet construction standards for laminated insulation boards and where spray techniques for foam insulations are employed. Chlorinated alkyl-phosphate esters are also frequently used in rubber, textile coatings, PVC compounds, cellulose ester compounds and coatings (UKWIR 2004). The esters are not chemically bound to the polymer chains, but the molecules are physically trapped in the matrices (NICNAS 2001). However, studies summarized in the Inchem (1998) report indicated that significant quantities of TDCPP in polyester garments were released to wastewater during washing (37 percent after 20 washings), which suggests that while encapsulated in polymer matrices, chlorinated flame retardants are appreciably mobile in these media and have the potential to be released to water. Organophosphorus compounds, such as TCEP and TCPP, have also been detected in indoor air with the main source being electronic equipment (Carlsson et al. 1997, Sjodin et al. 2001). This paper examined the occurrence of chlorinated alkyl-phosphate esters in the aquatic environment, evaluated the effectiveness of various unit operations to remove these compounds during water treatment, and studied the fate of these compounds in natural systems used for ground water augmentation.

Methods This study was initiated with a comprehensive literature review on production, occurrence, and fate of chlorinated alkylphosphate esters. Samples were collected from surface and wastewater at various locations within the United States. Additional monitoring of chlorinated flame retardants was conducted during nanofiltration, reverse osmosis treatment, riverbank filtration and soil-aquifer treatment. Details regarding the operational conditions of these processes are provided elsewhere (Drewes et al. 2003, Drewes et al. 2005, Amy and Drewes 2006). In this study, organophosphates, such as TCEP, TCPP and TDCPP, were quantified by gas chromatography and mass spectrometry. Samples were analyzed after solid-phase extraction (C-18) using an Agilent 6890A gas chromatograph coupled with a 5973 mass detector using a method adopted from Reddersen and Heberer (2003).

Results and Discussion Occurrence of chlorinated flame retardants in the environment Chlorinated alkyl-phosphate esters, such as TCEP, TCPP and TDCPP, have been reported to occur in the environment in studies from various countries. Table 2 summarizes some occurrence data for the three targeted chlorinated flame retardants in environmental samples. TCEP was quantified in seawater and river water samples in the mid 1980s in Japan (Ishikawa et al. 1985). All three chlorinated alkyl-phosphates were present in surface water samples collected in Germany with elevated concentrations in streams receiving wastewater discharge (Fries and Puettmann 2001, Andresen et al. 2004).

1.65 9.12

dipole moment#

molecular length [Å]+

O

O

P

7.749

9.87

3.38

1.6

N/A

1.526 ± 0.373

327.57

Cl

O

O

Cl

O

Cl

O

#

7.900

N/A

2.81

0.11

N/A

Calculated at unhydrated state by Hyperchem Software 7.0, with MM+ method

Calculated using Amsterdam Density Functional (ADF) version ADF2004.01 with the basis set Et-pVQZ

+

O

P

O

1.791 ± 0.771

430.91

Cl

Cl

Cl

C9H15Cl6O4P

Flame Retardant

13674-87-8

Cl

O

Cl

phosphate(TDCPP)

Tris(1,3-dichloro-2-propyl)-

*Calculated using Advanced Chemistry Development (ACD) Software Solaris V4.67, source: SciFinder Scholar 2002

6.991

8

Water solubilità (g/L)

molecular width [Å]

N/A

pKa (ACD)*

+

0.484 ± 0.36

Log KOW (ACD)*

Cl

285.49

O

P

molecular weight [g/mol]

Cl

O

O

Cl

Cl

chemical structure

C9H18Cl3O4P

C6H12Cl3O4P

Formula

Flame Retardant

Flame Retardant

Use

13674-84-5

phosphate(TCPP)

phosphate(TCEP) 115-96-8

Tris(1-chloro-2-propyl)-

Tris(2-chloroethyl)-

Physical and chemical properties of alkyl organophosphate esters

CAS Number

Table 1.

Table 2. Occurrence of chlorinated alkyl-organophosphate esters in the environment Source W ater

Study site Japan Germany

TCEP ng/L 14-347 121

TCPP ng/L N/A N/A

TDCPP ng/L N/A N/A

River water, seawater Rain water Rhine, Elbe, Main, Oder, Nidda and Schwarzbach Rivers Ruhr River (not wastewater impacted) Ruhr River (wastewater impacted) Rhine River Lippe River South Platte River (wastewater dominated) U.S surface water (median)

Reference

Germany

17-1510

N/A

N/A

Germany

N/A

5-20

N/A

Andresen et al. 2004

Germany

13-130

20-200

50

Andresen et al. 2004

Germany Germany Colorado, USA USA

N/A N/A 195-605

80-100 100 410-1220

13-36 17 200-400

Andresen et al. 2004 Andresen et al. 2004 this study

100

N/A

100

Ishikawa et al. 1985 Fries and Puettmann 2001 Fries and Puettmann 2001

Kolpin et al. 2002

Kolpin et al. (2002) investigated impaired surface water sources in the U.S. and reported that TCEP and TDCPP were present in 58 percent and 13 percent, respectively, of all samples analyzed. TCPP is used to more than 95 percent in polyurethane foams employed duringconstruction. It is therefore assumed that most of its residues found in surface water samples originates from construction activities, either by handlingof rigid foam plates or by usage of liquid spray foam (Andresen et al. 2004). Introduction of these compounds into surface water can occur via direct surface run-off and via wastewater discharge, such as combined sewer overflows (CSO), onsite wastewater treatment systems (OWS), and municipal and industrial wastewater treatment plant outfalls. The occurrence of all three alkyl-organophosphate esters in surface water samples varied between a few nanograms per liter to 1-2 microgram per liter. Amongthe three flame retardants, TDCPP exhibited the lowest occurrence range. The occurrence of TCEP, TCPP, and TCDPP in the South Platte River at Brighton, Colorado was monitored in this study by consideringthe stream flow conditions of the river. Results are illustrated in Figures 1-3. The South Platte River at this location is characterized as a wastewater dominated stream receivingthe majority of wastewater discharge from the Denver metropolitan area. Although there is a similar trend of lower occurrence of all three flame retardants duringspringrun-off conditions (due to dilution with mountain run-off), concentrations in the river still vary by several hundreds nanograms per liter duringconditions of relatively constant flow.

Figure 1. Occurrence of TCEP in the South Platte River, Brighton, Colorado

Figure 2. Occurrence of TCPP in the South Platte River, Brighton, Colorado

Figure 3. Occurrence of TDCPP in the South Platte River, Brighton, Colorado. Occurrence of chlorinated flame retardants in wastewater The occurrence of TCPP in raw sewage have been reported to show great day-today variation, with lower concentrations during weekends ((Meyer and Bester 2004). Several studies support, that chlorinated alkyl-phosphates were poorly eliminated during wastewater treatment and tended to pass through the biological processes unaffected (Meyer and Bester 2004, Marklund et al. 2005). All three chlorinated flame retardants exhibit modest hydrophobicity (log Kow below 2, see Table 1) and are expected to remain in the water phase. Since the discharge pattern of flame retardants to wastewater is site specific, concentrations of chlorinated alkyl-phosphates reported to occur in secondary treated wastewater effluents vary significantly (Table 3). In general, the occurrence of TCPP and TDCPP in treated wastewater samples seem to be higher as compared to TCEP. In same cases, concentrations in certain treated effluents in the same country were reported an order of magnitude higher for TCPP and significantly elevated for TCEP as compared to average concentrations observed in other effluent samples (Marklund et al. 2005). The elevated concentration at this facility was attributed to a discharger, who manufactures flame-retardant paints. In this study, samples were collected from various wastewater treatment plants across the United States in order to assess the occurrence of the three chlorinated flame retardants in treated effluents. All three chlorinated flame retardants were present in every treated effluent sample collected. In these samples, occurrence of TCEP, TCPP, and TDCPP varied between 290 and 900 ng/L, 770 and 3600 ng/L, and 280 and 1530 ng/L, respectively. The degree of treatment (not nitrified vs. nitrified/denitrified) does not seem to affect the concentration level of the target compounds, supporting earlier findings that flame retardants are poorly removed during conventional wastewater treatment.

Table 3. Occurrence of chlorinated alkyl-phosphate esters in wastewater Source W ater Wastewater, partially nitrified secondary effluents Wastewater, partially nitrified secondary effluents Wastewater, partially nitrified secondary effluent Wastewater, nitrified secondary effluent Wastewater, nitrified/denitrified secondary effluent Wastewater, not nitrified secondary effluent Wastewater, nitrified/denitrified tertiary effluent Wastewater, secondary effluents (median) Wastewater, not nitrified secondary effluent Wastewater, nitrified/denitrified tertiary effluent Wastewater, not nitrified secondary effluent Wastewater, nitrified/denitrified secondary effluent

Study site Sweden

TCEP ng/L N/A

TCPP ng/L