Understanding the practical issues of TBT contamination and ...

Understanding the
practical issues of
TBT contamination
and remediation
Mike Waldock
Centre for Environment Fisheries and Aquaculture Science, UK

Issue
• By the mid 1990’s TBT contamination of sediments
became the most common reason for refusal of a licence
for disposal of dredged material.
• Values up to 100ppm.
• Concs patchy and pointed to paint material entrained in
sediments.
• Biological availability of paint and/or remediation
possibilities were not clear.
• Defra sponsored a programme with Cefas between 1999
and 2002 to inform the risk assessment process. Project
leader – Jacquie Reed

Extent of the Problem
TBT
Levels
(mg/kg)
1998 1999 2000 2001
Total levels 1992-
2001
0-0.1 52% 46% 60% 65% 52% (1511)
0.1-1 38% 31% 32% 32% 30% (1049)
1-10 9% 17% 7% 3% 10% (293)
>10 1% 6% 0% 0% 2% (68)
2921
R. Tyne,Southampton Water, R. Tees, R. Mersey, R.
Humber and Newport, Barry and Cardiff.

Some Questions
• How much is adsorbed to the sediment,
entrained small/large paint particles?
• What sort of sediments are we dealing with?
• Is TBT more persistent or less persistent as
paint?
• Is it more or less toxic as paint?
• Is there evidence of harm at disposal sites?
• Do the different sediment types/TBT forms
respond differently to remediation?
• Is remediation cost-effective/fit in policy
framework?

TBT
Waste paint
(i)
(ii)
(iii)
Sediment
Large paint chippings
Small paint particles
TBT adsorbed to sediments

•
90
80
What sort of sediment particles is the TBT
associated with?
% of Particles with Size < 63 µm
70
60
50
40
30
20
10
0
0 20 40 60 80 100 120
TBT Concentrations (mg/kg)

Forms of TBT

TBT persistence
Fig 1. Flow-through 12°C, surface sediment
Concentration of TBT
µg/g dry wt
0.40
0.30
0.20
0.10
0.00
0 500 1000 1500
Day
Concentration of
TBT µg/g dry wt
0.50
0.40
0.30
0.20
0.10
0.00
Fig 10. Flow-through 12°C, anaerobic
sediment
0 500 1000 1500
Day

TBT persistence
Concentration TBT
ug/g dry wt
12
10
8
6
4
2
0
Artificially contaminated 12 C,
anaerobic sediment
0 200 400 600 800 1000 1200
Day

TBT and Metals in Lake
2000
Sediments
Mollusc shell
fragments
reappear
1960
Cu Hg TBT
Loss of
mollusc shell
fragments
change to
diatom
dominated
community

Toxicity
Arenicola
Corophium

Short and medium-term toxicity

TBT toxicity
100
Arenicola
% dead
TBTO
Paint
100
0
Control 0.1 1 10
Corophium
TBT (ppm)
% dead
TBTO
Paint
0
Control 0.1 1 10
TBT (ppm)

Sublethal response of paint-derived TBT
using A. marina (T=30 days)
Mean casting per replicate
125
100
Number of casts
75
50
25
0
control 0.95 mg.kg 2.21 mg.kg 2.96 mg.kg 7.80 mg.kg 8.00 mg.kg
TBT Concentration

Disposal sites
• Is the current risk assessment right for disposal
sites?
River Tyne
0 1
2
Kilometres
N
0.30 ppm TBT
0.15 ppm TBT
0.03 ppm TBT
Stn. 32
Tyne Dock
disposal
ground
Stn. 33
Stn. 39
Stn. 37

Changes in meofaunal ecology.
TBT-Transect off the Tyne 2000
Square-root transformation
Stress 0.15
39
32
N
39
32
River Tyne
37
39
37
37
39
37
33 33
32
Stn. 32
Stn. 33
Stn. 39
Tyne Dock
disposal
ground
Stn. 37
33
33
32
0 1
Kilometres
2
Station 32 inside the disposal ground
Station 33 inside the disposal ground (south of stn. 32)
Station 39 outside the disposal ground (south of stn. 33)
Station 37 outside the disposal ground (south of stn. 39)

Stage 3 imposex in female whelk

Dogwhelks
N
St. Mary's Lighthouse
4
3
1
2
River Tyne
Souter Lighthouse
S

Results
Incidence of Imposex in Dogwhelks After 6 months
100.0%
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
Incidence of Imposex
6 Month
Control
South of River
Mouth
North of River
Mouth
Site 4 Site 2

TBT in Marine Mammals
TBT in Porpoise liver
Northumb
Tyne &W
Teeside
N Yorks
Lincs
Norfolk
Suffolk
Essex
0 50 100 150 200
µg/Kg
TBT
Highest concentrations
close to Tyne estuary

Remediation

Summary of Techniques
Technique £/m 3
Mechanical Separation 5 - 35
Sediment Washing 25
Physico-chemical Extraction 30 – 210
Wet air oxidation, base
catalysed decomposition
30 – 735
Biological Microbial degradation 30 - 140
Thermal Thermal desorption 55 - 200
Immobilisation 30 – 125
Incineration 1000 – 2000
After Burt & Fletcher, 1999

Steam Stripping
Process
• Method developed in Germany (Eschenbach et
al., 2001)
• Remediates TBT, PAH and mineral oil in
sediment and soil systems.
• Treatment of contaminated fine-grained
particles
• Cleaning performances > 95%
• 14ppm Tyne sample – 0.1ppm +0.004ppm

Favoured Techniques
Mechanical
Hydrocyclone:
• Exploit differences in size and density between
paint flakes and particles for separation of
contaminated material. If TBT concentrated in
particular sediment size fraction, contaminated
material can be separated. Low cost and can be
incorporated on board a vessel.

TBT particles in sediments
Sediment contaminated at 4ppm
38µm 63µm 125µm 250µm 500µm
light 0.73 0.97 3.25 11.48 8.1
medium 0.44 0.22 2.05 1.85 4.01
heavy 0.21 0.32 0.2 1.84 3.46
Volume of banned material reduced by
up to 80%

TBT winnowing effect
TBT Concentration (mg/kg)
6.2
6
5.8
5.6
5.4
5.2
5
4.8
4.6
4.4
Flume T=3 hrs
100 200 300
Distance (mm) from w ater flow
0-4cm
4-8cm
8-12cm

Conclusions
• Chemical analysis of concentrations of TBT in sediment
can be misleading.
• Heavily contaminated sediments have TBT as both
entrained particles and adsorbed.
• Entrained paint is less toxic in the short term, but more
persistent
• Risk analysis analysis at disposal sites showed that TBT
is largely contained at the sites and is breaking down in
the disposed sediment
• TBT burdens can be reduced by mechanical methods
(lab only)