Environmental fate of Triclosan in the River Aire Basin, UK

Water Research 37 (2003) 3145–3154

Environmental fate of Triclosan in the River Aire Basin, UK

Darius Sabaliunasa,*, Simon F. Webbb, Armin Haukc, Martin Jacobc,William S. Eckhoffd

aProcter & Gamble Technical Centers Ltd., Rusham Park, Whitehall Lane, Egham, Surrey, TW20 9NW, UKbProcter & Gamble Eurocor, BelgiumcCiba Specialty Chemicals, SwitzerlanddThe Procter & Gamble Company, USA

Received 24 May 2002; accepted 21 March 2003

Abstract

The concentrations and removal rate of Triclosan, an antibacterial ingredient in consumer products, were measured

at advanced trickling filter (TF) and activated sludge (AS) wastewater treatment plants (WWTPs) in the River Aire

basin in the UK in September 2000. Additionally, the in-stream removal of Triclosan was measured directly in Mag

Brook, the stream receiving the treated effluent from the TF plant, using a fluorescent dye tracer to determine the water

plug travel times. The in-stream removal of the dissolved and un-ionized (i.e. bioavailable) fraction of the compound

was measured using semipermeable membrane devices (SPMDs) deployed at various distances downstream from the

WWTP discharge point. The estimated removal rates were used in the GREAT-ER (Geography-Referenced Regional

Exposure Assessment Tool for European Rivers) model to predict the site-specific distribution of Triclosan

concentrations in the Aire basin as well as to calculate regional concentrations. High WWTP (B95%) and in-stream(0.21–0.33 h�1) removal rates of Triclosan in Mag Brook confirm that this chemical is rapidly eliminated from the

aquatic environment.

r 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Triclosan; Environmental fate; GREAT-ER; SPMD; Exposure modelling

1. Introduction

Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol;

CAS# 3380-34-5, Fig. 1) is an antibacterial agent and

a preservative approved by the EU Cosmetics Directive

[1]. Its widespread use in consumer products, including

cosmetics, is determined by its bacteriostatic efficacy

against a broad spectrum of microorganisms [2] and a

favorable human safety profile [3]. In cosmetic products

such as toothpastes, mouth rinses, soaps, shampoos,

deodorants, skin care creams and lotions, its concentra-

tion is typically in the range of 0.1–0.3%.

Triclosan (MW=289.5) is a non-volatile

(VP=4� 10�6mmHg at 20�C) [2] and poorly solublein water (10mgL�1 at 20�C) organic compound with an

estimated logKow of 4.8 [4]. One of the main routes this

compound enters the environment is with personal care

and other consumer products that are washed down-the-

drain during their normal use. The concentrations and

distribution of Triclosan in the aquatic environment are

governed by its consumer use pattern, removal rate

during wastewater treatment, partitioning (sorption and

ionization) and chemical and biological degradation in

surface waters. Triclosan has been shown to undergo

complete biodegradation in a batch activated sludge test

and to be highly removed in a continuous activated

sludge treatment system [2]. Even though hydrolytically

stable, in the aquatic environment, Triclosan is subject

to photolytic transformation with an estimated half-life

of less than an hour in natural sunlight [2,5,6].

Understanding the processes that determine the fate

of Triclosan in the aquatic environment is important for

the estimation of its environmental exposure and*Corresponding author. Tel.: +44-1784-498615.

E-mail address: [email protected] (D. Sabaliunas).

0043-1354/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0043-1354(03)00164-7

assessment of the associated environmental risk. The

wastewater treatment and in-stream removal rates of

Triclosan may be used in generic mathematical distribu-

tion and exposure models to estimate its predicted

environmental concentration (PEC) in various environ-

mental compartments. Such an approach is used, for

example, in the Technical Guidance Documents (TGDs)

supporting the European Union’s current chemical

legislation [7] to predict ‘‘regional’’ and ‘‘local’’ con-

centrations of a substance undergoing environmental

risk assessment. Even though a ‘‘generic scenario’’

provides a reasonable approximation of substance’s

environmental fate and exposure, it does not account for

spatial and temporal variability in emissions, regional

infrastructure, river flow rates, dilution factors, physical

chemical conditions and other important parameters.

This often invokes the use of conservative assumptions

and application factors to account for worst-case

situations. A ‘‘reality-check’’ of such generic models

may be accomplished via the use of environmental

monitoring data in advanced GIS-based models capable

of predicting site-specific chemical concentrations using

the available underlying environmental databases [8].

The current study was undertaken in order to better

understand the fate of Triclosan in the aquatic environ-

ment and to generate the necessary data for its site-

specific and regional exposure assessments. The primary

objective of the study was to measure the environmental

loadings, concentrations and removal of Triclosan

during wastewater treatment and in river water under

the North European conditions. The second objective

was to use the estimated parameters to model the

concentration distribution of Triclosan in a real river

catchment using GREAT-ER, a GIS-based regional

exposure assessment model.

2. Methods

2.1. Study area and study sites

The River Aire basin is situated in Yorkshire, north of

England. It comprises four catchments, Aire, Calder,

Went and Rother. The River Aire drains the central

Pennines and flows south-eastward through the West

Yorkshire metropolitan area and the Yorkshire coal-

field, where it is joined by the Calder, its major tributary.

This area is characterized by a high population density,

large number of small tributaries and medium to small

size wastewater treatment plants with wastewater dilu-

tions factors as low as 2 (Table 1, [9]).

Based on the default environmental infrastructure

data from GREAT-ER (see below), two wastewater

treatment plants (WWTPs) were selected for the study

carried out in September, 2000. The Crofton activated

sludge (AS) plant southeast of Wakefield serves a

population of about 9000 people with the average

wastewater flow of 1800m3 day�1

(200L � capita�1 � day�1), and the Meltham trickling

filter (TF) plant south of Huddersfield serves a popula-

tion of 7900 people with the average wastewater flow of

4100m3 � day�1 (520L � capita�1 � day�1). The latter

plant operates two consecutive series of trickling filters

and should effectively be regarded as an advanced

secondary treatment plant. In both plants, nearly all of

the influent (>98%) is composed of domestic waste-

water. The historic WWTP performance data (York-

shire Water) showed that both plants operated well, with

the effluent biological oxygen demand (BOD) values

typically in the range of 3–10mgL�1. This was

confirmed during the reconnaissance trip to the plants

in July, 2000, in which the measured BOD, total

suspended solids (TSS) and linear alkylbenzene sulfo-

nate (LAS) removal rates based on grab influent and

effluent samples were 95%, 92% and 99.6%, respec-

tively, at the Meltham WWTP, and 97%, 93% and 98%

at the Crofton WWTP. LAS was used in the study as a

benchmark chemical for WWTP removal rates, as it is a

common surfactant used in detergents and has a well

established environmental fate profile.

The Crofton WWTP discharges the treated effluent

directly into the River Calder, whereas the Meltham

WWTP discharges into Mag Brook, which is part of the

Calder catchment. The in-stream removal of Triclosan

was studied in the 3.5-km section of Mag Brook directly

Cl

OH

O

Cl

Cl

Fig. 1. Chemical structure of Triclosan.

Table 1

Main characteristics of the Aire and Calder catchments (from

Fox et al. [9])

Catchment Aire (above

confluence with

Calder)

Calder

Area, km2 1100 957

Population 1,100,000 790,000

Number of WWTPs 40 23

Dry weather flow, m3 s�1 9 10

Mean flow, m3 s�1 16.5 17.8

5th-percentile flow, m3 s�1 5.4 6.9

D. Sabaliunas et al. / Water Research 37 (2003) 3145–31543146

below the WWTP discharge point. Mag Brook (Table 2)

is a small and shallow natural stream with a relatively

constant water flow rate, velocity, width and depth over

the entire stretch used for the study, except for the

farthest downstream site where the flow velocity drops

as the river becomes wider and deeper. The river bottom

is mainly covered by rocks, and sediments are only

found at the downstream end of the stretch, where the

lower flow velocity and deeper waters favor the settling

down of suspended matter.

2.2. Wastewater sampling

Hourly time-proportional composite influent, primary

effluent and final effluent samples were collected at both

selected WWTPs over the time period of 24 h using

ISCO (Model 3600) automatic samplers. Immediately

upon collection, before compositing, the individual

samples collected at odd hours were acidified with

concentrated phosphoric acid to pHo2. The samplescollected at even hours were preserved with 3% formalin

(v/v). The individual samples preserved with phosphoric

acid and formalin were composited separately. The

composite samples preserved with phosphoric acid were

spiked with 13C-labeled Triclosan standard and shipped

on ice to the Ciba SC analytical laboratory (Basel,

Switzerland) for determination of Triclosan. The for-

malin-preserved composite samples were submitted to

the local laboratory of the Environment Agency (Leeds,

UK) for the analysis of LAS. Additionally, unpreserved

grab samples of influent, primary effluent and final

effluent were taken at each site in the early afternoon

hours on the same day when composite samples were

collected. These samples were also analyzed at the

Environment Agency’s laboratory for conventional

water quality parameters such as biological oxygen

demand (BOD), conductivity, pH, total suspended

solids (TSS), total organic carbon, ammonia, total

nitrogen, phosphorus, calcium, magnesium, etc.

The weather conditions were generally dry through-

out the entire sampling period, except for a short rainfall

event during sampling at Meltham. Based on the

measurements by flow gauges installed at both plants,

the daily integrated flow rates during the sampling

period were 4140m3 day�1 (524L � capita�1 � day�1) atthe Meltham WWTP and 1385m3 day�1

(156L � capita�1 � day�1) at the Crofton WWTP. At thelatter plant, the flow rate was lower than the yearly

average value from GREAT-ER (1800m3 day�1), con-

sistent with the dry weather conditions at the time of the

study, whereas at the Meltham WWTP, it was similar to

the yearly average, possibly reflecting on the rainfall

event and/or groundwater infiltration during the sam-

pling.

2.3. In-stream removal

The study was carried out following the guidelines by

the US Geological Survey [10,11]. An approximate

water travel time was estimated in a pilot study carried

out during the reconnaissance trip to the study area in

July 2000. In the pilot study, Fluorescein dye (Sigma-

Aldrich) was released at the WWTP discharge point,

and the colored water plug was visually followed

downstream. At the same time, water flow velocity,

depth, width, water temperature, conductivity, dissolved

oxygen (DO) measurements were taken. River flow rates

at several sites were calculated based on the river width

at these sites and cross-sectional flow velocity and depth

measurements. Importantly, the river perimeter was

carefully inspected for any additional water inflows. It

was determined that there were no additional water

inflows along the entire 3.5 km river stretch selected for

the study, which was also confirmed by rather uniform

water conductivity values measured at various points

Table 2

Characteristics of the Mag Brook stretch used in the in-stream removal study, default GREAT-ER and measured values

Default GREAT-ER values

Mean 5th percentile Measureda

Flow rate, m3 s�1 0.526 0.149 0.13–0.18

Flow velocity, m s�1 0.218 0.117 0.015–0.57

Length, m 3464 N/A 3464

Depth, m 0.547 0.348 0.05–0.47

Width, m N/A N/A 2–6.1

Meltham WWTP discharge, m3 s�1 0.049 N/A 0.048b

Flow-based dilution factor 10.7 3.0c 2.65

Conductivity-based dilution factor N/A N/A 2.94

aAt the time of study.bDaily average during study period (5 days).cBased on the daily average WWTP flow rate (default GREAT-ER values).

D. Sabaliunas et al. / Water Research 37 (2003) 3145–3154 3147

downstream the stretch. Five sampling sites were

selected for the study, mainly based on the ease of

access to the river. One of these sites was located about

50m upstream from the WWTP effluent discharge

point, the other four were 20, 750, 1500 and 3500m

downstream from the discharge point. The stream

section between the WWTP discharge point and the

first downstream site was narrow (2m wide) and highly

turbulent, ensuring full water mixing at this site as was

also confirmed in the pilot study using the Fluorescein

dye. At all of these sites, sets of 4 semipermeable

membrane devices (SPMDs) were deployed in the river.

Additional 4 SPMDs were retained as field blanks.

SPMDs are membrane-based time-integrated passive

samplers capable of bio-mimetic preconcentration of

moderate to highly hydrophobic chemicals from water,

sediments, soil or air [12]. The SPMDs used in the

current study were of standard configuration (96 cm

long, 1 g triolein; from Environmental Sampling Tech-

nologies, St. Joseph, MO), placed in protective steel

mesh containers. At all sites, the SPMDs were exposed

to the running river water, except for the farthest

downstream site, where river sedimentation occurred,

and the SPMDs were found to have been buried in the

sediment. The SPMDs were collected at the time of the

main study, with the resultant exposure period of 5

weeks. After the exposure, the SPMDs were sealed in

stainless steel cans and shipped on ice to the analytical

laboratory for Triclosan analysis.

On the day of the main study, September 8, 2000, the

hydraulic residence times at the sampling sites were

determined using the Rhodamine WT (Crompton

Colors, Gibraltar, PA) dye tracer with fluorescent

detection. Briefly, 180mL of the dye (20% aqueous

solution) was released into the river water directly below

the WWTP discharge point. The amount of the dye

released was calculated using an empirical equation [11]

to give the peak dye concentration of about 10 mgL�1 atthe farthest downstream site. The dye concentration at

each site was monitored using continuous flow fluorom-

eters with automatic data logging capability (Turner

Designs, Model 10-AU-005-CE). At the time when the

dye reached peak concentration, four 1L river water

samples were taken at each site across the river section.

Three water samples were preserved with phosphoric

acid as described above for wastewater samples, and the

remaining sample was submitted immediately to the

local laboratory of the Environment Agency for the

analysis of conventional water quality parameters (same

as for wastewater samples). The preserved samples were

spiked with 13C-labeled Triclosan standard and shipped

on ice to the analytical laboratory for Triclosan analysis.

On the day of the study, additional river flow velocity

and flow rate measurements were also carried out as

described above (Table 2). The measured flow rate was

close to the 5th percentile of the yearly distribution of

flow rates (default GREAT-ER data) in the studied

section of Mag Brook. This low flow rate observed in the

study was probably due to a long period (>2 months) of

dry weather conditions preceding the study.

2.4. Sample processing and analytical

Details of the analytical method used in the current

study are described elsewhere [13]. Briefly, an aliquot of

each WWTP sample was mixed with concentrated

sulfuric acid and extracted with hexane/dichloro-

methane mixture. An appropriate aliquot of each extract

was derivatized with a silylating agent and measured by

GC/MSD in a single ion monitoring (SIM) mode.

Quantification was carried out using the isotope dilution

method, based on the 13C-labeled Triclosan on-site

spike.

River water samples were applied to solid phase

extraction cartridges, which were subsequently extracted

using supercritical fluid extraction (SFE) with pure CO2.

The SFE extracts were derivatized with a silylating agent

and analyzed with GC/MS as described above.

The SPMDs were rinsed with running distilled water

and air-dried. Three SPMDs from each site were

combined together and dialyzed at 20�C in 500mL of

hexane for 48 h, with the solvent replacement after 24 h,

resulting in the total of 1000mL of dialyzate. The

dialyzates were reduced to a known volume, filtrated

through anhydrous Na2SO4 and spiked with13C-labeled

Triclosan. An aliquot of each extract was derivatized

with a silylating agent and analyzed by GC/MSD in the

same way as the extracts from water.

2.5. GREAT-ER model

The River Aire and three related river catchments

(Calder, Went and Rother) have been modeled in

GREAT-ER, the Geography-Referenced Regional Ex-

posure Assessment Tool for European Rivers (version

1.02). GREAT-ER combines environmental models and

GIS techniques to predict and visualize the concentra-

tion of down-the-drain chemicals in several European

river catchments [14]. The output of the GREAT-ER

software is chemical’s site-specific Predicted Environ-

mental Concentrations (PECs), which can also be

integrated for the whole catchment using various

weighting methods [15]. The chemical-specific input

data are physical, chemical and biochemical parameters,

together with geographical production and consumption

patterns. The GREAT-ER project is managed by a task

force of ECETOC (European Centre for Ecotoxicology

and Toxicology of Chemicals). More information on

this model and its application areas can be found on the

GREAT-ER website (www.great-er.org).


http://www.great-er.org

3. Results and discussion

3.1. Wastewater treatment removal

Concentrations of Triclosan in the influent, primary

effluent and final effluent at both wastewater treatment

plants and the calculated removal rates are presented in

Table 3, along with the measured concentrations of LAS

and water quality parameters, including BOD. Concen-

trations of Triclosan and LAS in the influent of the

Meltham plant were considerably (2–3 fold) lower

compared to the Crofton plant, probably due to the

significantly higher per-capita water flow at the former

plant pointing to likely dilution of influent with

Triclosan- and LAS-free water from other, unidentified

sources such as groundwater infiltration. However, the

calculated (based on the population served by the plants,

wastewater flow rates and influent concentrations) per-

capita use of Triclosan was similar for both plants

(1400mg � capita�1 � year�1 for Meltham WWTP and

1240mg � capita�1 � year�1 for Crofton WWTP) indicat-ing that the distribution and use of Triclosan-containing

consumer products is rather uniform in this region.

The results of the current study demonstrated that

Triclosan was extensively removed (B95%) during bothactivated sludge and advanced trickling filter wastewater

treatment. Triclosan removal rates were somewhat lower

than those of LAS, BOD and comparable to those of

organic carbon. The WWTP influent concentrations and

removal rates at Meltham and Crofton plants are

comparable with other recent Triclosan measurements

in the US and the UK. At several wastewater treatment

plants in Ohio, US, the measured Triclosan concentra-

tions in influent were in the range of 3.8–16.6 mgL�1,whereas the wastewater treatment removal rates ranged

from 58% to 86% at three trickling filter plants and

were approximately 96% at two activated sludge plants

[13]. Triclosan removal at Stretford (Greater Manche-

ster, UK) trickling filter plant has been measured at

79%, and its removal at Crewe (Cheshire, UK) activated

sludge plant was 83% (unpublished data from a Procter

& Gamble study, 1997). In the latter study, influent

concentrations were 2.8 and 5.4 mgL�1, respectively.

3.2. In-stream removal

Concentrations of Triclosan in river water and the

calculated in-stream removal rates are presented in

Table 4. It is important to note that Site E, the farthest

downstream site, was excluded from the rate calcula-

tions due to its significantly higher suspended solids

concentration compared to the upstream sites. As noted

above, the visual inspection of the river bottom

indicated that river sedimentation occurred at this site.

The SPMDs at this site were also found to be fully

submerged in sediment at the time of recovery. The

elevated suspended solids at site E may reflect dis-

turbance of sediments at the time of sampling and thus,

the measured total concentration of Triclosan in water

at this site included a contribution from its solids-

associated fraction distorting the concentration die-

away data in the aquatic compartment. Similarly, the

SPMDs at site E were exposed to the sediment

interstitial water with Triclosan concentrations different

from those in the running water column. Meanwhile,

there were no substantial sediments in the river stretch

from site B to site D with the river bottom being covered

with rocks. In this stretch, going downstream, the

suspended solids concentration decreased from 9 to

6mgL�1, while the river water pH values increased from

Table 3

Wastewater treatment removal of BOD, organic carbon, suspended solids, LAS and Triclosan at Meltham and Crofton wastewater

treatment plants

BODa

(mgL�1)

Organic carbona

(mgL�1)

Suspended solidsa,

(mgL�1)

LAS

(mgL�1)

Triclosan

(mgL�1)

Meltham WWTP (trickling filter)

Influent 204 151 228 1.71 7.5

Primary effluent 55.3 33.2 56 2.4 5.9

Final effluent 2.7 5.88 14 0.029 0.34

Primary removal, % 72.9 78 75.4 0 21.3

Total removal, % 98.7 96.1 93.9 98.3 95.5

Crofton WWTP (activated sludge)

Influent 262 126 166 3.18 21.9

Primary effluent 230 142 120 2.88 13.35

Final effluent 4.1 21.4 14 0.016 1.1

Primary removal, % 12.2 0 27.7 9.4 39

Total removal, % 98.4 83 91.6 99.5 95

aBased on grab unpreserved samples.


6.94 to 7.18. Even though these changes may seem

insignificant, Triclosan is a sorptive and ionizable

compound, and any changes in the suspended solids

concentration and water pH values could have caused its

repartitioning between the sorbed and freely dissolved as

well as protonated and ionized forms, which in turn

could have influenced the overall removal rate. To

estimate the proportion of various forms of Triclosan

from its total concentration, one can use the following

partitioning equations [16]:

Csole-union ¼CT

½1þ 10ðpH�pKaÞ þ KOCfOCM;

Csol-ion ¼ Csol-union10ðpH�pKaÞ;

Csor-union ¼ ðKOCfOCMÞCsol-union;

where Csol-union; Csol-ion and Csor-union are the concentra-

tions of dissolved unionized, dissolved ionized and

sorbed compound, respectively (mgL�1), CT is its total

concentration, pKa is the acid dissociation constant

(8.14 for Triclosan [17]), KOC is the water/organic

carbon partition coefficient (46,800Lkg�1 for Triclosan

[2], fOC is the fraction of organic carbon of suspended

solids (assumed to be 0.13), and M is the suspended

solids concentration (kgL�1). Using the above equa-

tions, it can be calculated that from site B to site D, the

proportion of sorbed Triclosan decreased from 4.9% to

3.2% of the total measured water concentration,

whereas the proportion of ionized Triclosan increased

from 5.6% to 10.2% of the total concentration. These

changes were considered insignificant in the view of

natural variability associated with this type of measure-

ments, and thus, the calculated Triclosan in-stream

removal rates in that river section were not corrected for

its repartitioning due to sorption and ionization.

In river water, the Triclosan removal rate was

comparable to or even higher than the rate of BOD

decay (Table 4, Fig. 2). The estimated SPMD-based in-

stream removal rate (0.33 h�1, t1=2 ¼ 2:1 h) was some-what higher than the rate based on the grab water

samples (0.21 h�1, t1=2 ¼ 3:3 h). The rate based on thewater samples reflects the total loss rate of all forms of

Triclosan due to chemical (photolysis) and biological

degradation and, to a smaller extent, settling of

suspended solids with sorbed Triclosan. SPMDs, on

the other hand, sample only truly dissolved and union-

ized (i.e. bioavailable) compound. The SPMD data

therefore reflect the time-integrated loss rate of the

dissolved and protonated form of Triclosan over the

exposure period of 5 weeks. Thus, the factors that may

have determined the higher SPMD-based removal rate

compared to the rate based on the grab water samples

include different exposure conditions and duration,

increase in pH downstream (resulting in increased

ionization of Triclosan diminishing its availability to

SPMDs) and a higher loss rate due to degradation

versus the total loss rate that includes settling.

Interestingly, the in-stream removal rate of Triclosan

in Mag Brook was significantly higher than its removal

Table 4

Measured conductivity, suspended solids, BOD and Triclosan concentrations in Mag Brook upstream (Site A) and downstream (Sites

B–E) from the Meltham WWTP effluent discharge point and calculated in-stream removal rates

Conductivity Suspended

solids

(mgL�1)

pH BOD

(mgL�1)

Organic

carbon

(mgL�1)

Triclosan

mS cm�1 Dilution Water (ngL�1)

(mean7SE,n ¼ 3)

SPMD

(ng/3

units)

Site A (50m upstream) 175 — 10 7.18 3.9 6.36 1971.4 93

Site B (20m downstream,

travel time 1min)

352 2.94a 9 6.94 3.6 9.28 80715 489

Site C (750m downstream,

travel time 55min)

282 1.25b 7 7.12 2.4 7.53 5373.2 423

Site D (1500m downstream,

travel time 165min)

293 1b 6 7.21 2.2 7.07 4375.6 205

Site E (3500m downstream,

travel time 310min)

316 1b 51 7.18 3.1 5.95 4474.2 399

Die away rate B–Dc, h�1

(slope7SE)N/A 0.1470.05 N/A 0.1670.08 0.0970.04 0.2170.08 0.3370.06

aDilution of effluent by river water at the point of discharge, based on conductivity.bDilution of river water flow between this site and the preceding site, based on conductivity.cSite E was excluded from the rate calculations as the SPMDs at this site were found to be submerged in sediment at the time of

recovery. Elevated suspended solids at Site E may reflect disturbance of sediments at the time of sampling.


rate measured in a similar study in Cibolo Creek in

Texas, US [16]. In Cibolo Creek, the removal of

Triclosan was studied over an 8 km-long section of the

river downstream from a trickling filter WWTP effluent

discharge point using bromide as a conservative tracer

to estimate the water plug travel time. The total loss rate

of Triclosan from the water column was 0.06 h�1, i.e.

3.5–5.5 fold less than the rate observed in Mag Brook.

This observed difference may be due to several reasons.

One of them is a different degree of photolysis

contribution to the overall rate of Triclosan removal in

these streams. It has been shown that Triclosan under-

goes rapid photolytic transformation in surface waters

under a natural sunlight with the estimated half-life less

than an hour and as short as 15min [2,5,6]. The direct

photolysis of the anionic form appeared to be the major

elimination process for Triclosan in Swiss lake water

[5,6]. It was shown in the latter study that the rate of

photolytic transformation of Triclosan was dependent

on a number of natural factors, with water pH, solar

light intensity and surface water depth being amongst

the most important of them. Specifically, the rate of

direct phototransformation of Triclosan increased 30-

fold with an increase in pH from 5.9 to 11.0. Further, at

the lake water depth of 50 cm, the rate was only 5% of

the rate at the water surface indicating that 95% of the

photochemically active sunlight was absorbed in the

upmost 50 cm of the lake water. Even though the

measured water pH values were rather similar in Mag

Brook and Cibolo Creek, the latter stream was

reportedly turbid, significantly deeper (0.4–1.5m com-

pared to 0.005–0.47m in Mag Brook, Table 2), and less

turbulent than Mag Brook. It seems likely, therefore,

that conditions for photolysis in Cibolo Creek were not

as favorable as in Mag Brook due to a lesser availability

of photochemically active sunlight in the overall water

column.

Naturally, there may have been other environmental

factors that contributed to the observed rate differences

between Mag Brook and Cibolo Creek, including

different Triclosan sorption and solids settling rates as

well as differences in biodegradation rates due to

different amount of surface biofilm present in these

two streams.

3.3. GREAT-ER simulation

High dependency of substance-specific aquatic fate

processes on a broad spectrum of environmental factors

has significant implications for regional fate models such

as GREAT-ER, which use experimental parameters

(WWTP, in-stream removal rates) determined at one or

several sites to model the fate and distribution of

substance’s concentrations on a larger scale or even in a

different region. Even though a large number of river

stretches in the Aire basin are similar in properties to

Mag Brook, the downstream sections of the basin may

become more turbid and deep (up to 2m in depth), with

less favorable conditions for photolysis and other

removal processes. Thus, the in-stream removal rate

determined in Mag Brook cannot be directly applied in

the model for the whole river basin. To be able to more

accurately predict site-specific concentrations of Triclo-

san in the Aire basin as well as to use the Mag Brook

rate in other river basins, it would be important to

quantify all the processes that may affect the overall

removal rate of Triclosan in a river system, including

photolysis, biodegradation, sorption and solids settling

rates. The rate of photolysis, for example, will depend

on water pH, solar light intensity, which is a function of

latitude and year seasonality, river depth, suspended

solids concentration, and water convection (turbulence)

rate. Biodegradation will depend on water temperature,

which varies considerably throughout the year and at

different water depths and the amount of surface

biofilm, which is proportional to the water surface area

to volume ratio. Sorption will depend on water pH and

the amount of suspended solids present in the water

column as well as their characteristics such as organic

carbon content and the particle size distribution. With-

out such adjustments, the in-stream removal rate

measured in the current study could be directly used to

describe the removal of Triclosan in small and shallow

streams of Northern Europe similar in their properties

to Mag Brook.

Further, the wastewater treatment removal rate of

Triclosan measured at the Meltham trickling filter plant

may not be representative of other trickling filter plants

in the region and elsewhere, which do not have advanced

secondary treatment system as at the Meltham plant

(two consecutive series of trickling filters).

To avoid bias in a regional model due to the use of

site-specific data that may not necessarily be representa-

tive of the whole region, one can carry out an

uncertainty analysis of the distribution of experimental

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140 160 180

Time, min

Con

cent

ratio

n lo

ss, %

BOD

TCS - water

TCS - SPMDs

Fig. 2. Loss of BOD and Triclosan (TCS) in Mag Brook

downstream from the Meltham WWTP effluent discharge

point.


substance-specific fate parameters. Such an approach

was used in the GREAT-ER model. The input

parameters (Table 5) were variables represented by

normal (WWTP removal) or uniform (in-stream re-

moval) distributions of rates based on the experimental

values from the current study and other studies referred

to in this paper. In the model simulation, the Monte-

Carlo sampling (5000 iterations) of these distributions

and the yearly distribution of Mag Brook flow rates

(default GREAT-ER values) was used to simulate the

site-specific concentrations of Triclosan in the basin

(Figs. 3 and 4). Using various methods, these concen-

trations can be spatially aggregated to a single value of

PEC representing exposure in the basin (Table 6).

PECinitial represents an unweighted average of initial

river concentrations directly below each wastewater

effluent discharge in the basin, and as such, it is

equivalent (but not identical) to PEClocal used in the

Technical Guidance Document (TGD) for environmen-

tal risk assessment in the EU [7]. PECcatchment represents

a weighted aggregated exposure value for the entire

basin, and it is similar to the concept of PECregional used

in the EU TGD. By means of various weighting

methods, PECcatchment can be calculated including all

stretches (i.e. both receiving and not receiving waste-

water effluent discharge) or exposed stretches only (i.e.

receiving wastewater effluent discharge). Volume-

weighted PECcatchment based on all stretches and flow

increment-weighted PECcatchment based on impacted

stretches only have been shown to be the most

representative aggregated PEC values as they can best

resolve scale-dependencies [15].

Table 5

GREAT-ER input parameters

Parameter Value Comments

Per-capita use of Triclosan 1340mg � capita�1 � year�1 Based on measured wastewater flow rate (520L � capita�1 � day�1 atMeltham WWTP and 156L � capita�1 �day�1 at Crotfon WWTP),influent concentration (Table 3) and known population size served

by the Meltham (7900) and Crofton (8900) WWTPs, average for

both plants (no distribution assumed in the model)

Wastewater treatment

primary removal rate

31.0712.8% (normal

distribution)

Based on reported measured values, including the current study (8

values in total)

Trickling filter WWTP

overall removal rate

80.2713.9% (normal

distribution)


values in total)

Activated sludge WWTP

overall removal rate

92.276.5% (normal

distribution)


values in total)

In-stream removal rate 0.06–0.33 h�1 (uniform

distribution)

Based on measured values in Cibolo Creek and Mag Brook

Monte Carlo iterations 5000

Fig. 3. Graphic representation of mean Triclosan concentrations in the Aire and Calder Basin predicted by GREAT-ER simulation.


Several important factors should be considered when

interpreting the modeled concentrations and especially

when using them for environmental risk assessment

purposes. The simulated PECs at any point in the basin

represent very approximate estimates only due to wide

ranges of input parameters (especially the in-stream

removal rate) used in the model calculations. For the

reasons discussed above, it is likely that the predicted

concentrations in the upstream sections of the basin

(shallow and clear streams, higher removal rate ex-

pected) overestimate the actual concentrations, whereas

in the downstream sections (deep and turbid, slower

removal), they underestimate the actual levels. It is also

worth noting that trickling filter wastewater treatment

plants in the US are operated in a slightly different way

than TF plants in the UK. Plants in the UK generally

achieve higher removal rates for consumer chemicals,

and thus, the use of the US removal data in the model

calculations may have caused a bias toward over-

estimating PECinitial, and, consequently, the downstream

concentrations. The simulated concentrations of Triclo-

san in Mag Brook illustrate the importance of these

factors (Table 7). The calculated mean concentrations

were higher than the measured concentrations, even

though the measurements were made under low flow

conditions (close to the 5th percentile, Table 2), when

higher than the yearly average levels of Triclosan could

be expected in the river water due to lower dilution

factors.

The large standard deviations associated with the

model estimates reflect the wide spread of input

parameters used in the model calculations. Thus, the

calculated standard deviations and, importantly, the

90th percentile values of the regional estimates do not

merely reflect the variability of PEC that can be expected

in the river basin. They are rather a combination of the

variability and mathematical uncertainty of the mean,

and as such, they can hardly be applied directly in

environmental risk assessment as probabilistic PECs.

For risk assessment purposes, therefore, the calculated

mean PEC values should be used.

4. Conclusions

The results of the current study confirm that Triclosan

is not a persistent chemical. It was extensively removed

during wastewater treatment, with the measured re-

moval rate at both advanced trickling filter and

activated sludge wastewater treatment plants of about

95%. In river water of Mag Brook, concentrations of

Triclosan further declined rapidly, with the measured in-

stream removal rate in the range of 0.21–0.33 h�1,

(t1=2 ¼ 2:123:3 h). This rate was comparable to or evenhigher than the BOD removal rate. The in-stream

removal rate measured in the current study is character-

istic of and may be directly applied to small and shallow

streams of Northern Europe. In other rivers, this rate

should be adjusted to account for factors that influence

the fate of Triclosan in the aquatic environment,

Table 6

Concentrations of Triclosan in the Aire and Calder Basin

simulated by GREAT-ER

Calculated

concentrations

(ngL�1)

Weighting

method

PECcatchment (all stretches)

Mean 45.1 Volume

90th percentile 94.2

PECcatchment (exposed stretches)

Mean 52.0 Flow

increment

90th percentile 109.3

PECinitial (mean) 334.9 Not

weighted

Table 7

Measured and simulated by GREAT-ER concentrations of

Triclosan in Mag Brook

Calculated by

GREAT-ER,

Mean7SD(ngL�1)

Measured

(ngL�1)

Csim (start of the stretch) 1277146 80

Csim (end of the stretch) 46.2749.2 44

Csim (90%)a 161

a90th percentile of the concentration distribution for the

whole river stretch.

Horbury

DewsburyHuddersfield

Deighton

Brighouse

Meltham

Caldervale

Stanley Pinder Green

Mill LaneWheldale

Sutton

0

20

40

60

80

100

120

140

River length, km

Con

cent

ratio

n, n

g/L

Fig. 4. An example profile of mean Triclosan concentrations

simulated by GREAT-ER downstream from Mag Brook (Mag

Brook–Holme–Calder–Aire). The concentrations represent

internal means for each stretch.


specifically, the rate of photolysis, biodegradation and

settling.

The GREAT-ER model is a useful tool for predicting

and visualizing site-specific concentrations of down-the-

drain chemicals, however, a good knowledge of factors

influencing the fate of the compound of interest in a

varied environment is necessary for the correct inter-

pretation and use of the model data. Ideally, such key

parameters as the in-stream removal rate should also be

geo-referenced, or more robust probabilistic approaches

should be employed to account for the fate parameter-

related spatial variability.

Acknowledgements

The authors would like to thank Drew McAvoy,

Geert Boeije, Nick Fendinger, Scott Dyer, Donna

Morrall and Diederik Schowanek for the critical review

of the manuscript and their valuable comments. We also

would like to thank the heeds office of the UK

Environment Agency for their practical help in con-

ducting this study.

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