Heavy Metals Special Topic: Tributyltin

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Heavy Metals Special TopicTributyltin

• BIOL4000/5000
• Topic 11

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Learning goals

• To understand sources and environmental fate of
  tributyltin
• To learn mechanisms of endocrine disruptors using
  TBT as an example
• To understand the general mechanism of EPA
  criteria for water quality

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Sources of TBT in the biosphere
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Organotins

• Stabilizers of plastics
• Biocides
• Fungicide
• Insecticide
• Bactericide
• Anti-fouling paints

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Negative effects of fouling

• Increases drug
• Reduces speed
• Increases fuel consumption
• Requires frequent (and expensive) cleaning and
  re-painting

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Antifouling paints

• Copper-containing
• Mercury-containing
• 1970-1980 TBT-containing

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Tributyltin (TBT)
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Anti-fouling effects of TBT
Image by M T Chemicals Inc., Woodbridge, NJ.
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TBT in the environment

• Slow biodegradation
• Up to 5 month under aerobic conditions and 1-2
  month under anaerobic conditions
• Accumulates in water and sediment
• Marinas
• Harbours
• Bioaccumulation

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Environmental TBT concentrations are correlated
with navigational activity
Strand Asmund (2003)
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Imposex
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Morphology of imposex in snails
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Imposex as a biomarker for TBT pollution

• Experimental studies show direct causal link
  between TBT exposure and the incidence of imposex
• Field studies show strong correlation between TBT
  concentration and the incidence of imposex
• Easy to score
• U.K. and Canada community-based biomonitoring
  programs

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Mechanisms of TBT-induced imposex
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Steroid hormone metabolism
TBT
P450 aromatase
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TBT disrupts hormonal balance in shellfish
Ruditapes decussatus
Testosterone levels
Rates of conversion of testosterone to estrogens
Morcillo Porte 2000
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Shell chambering in oysters
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Is it all just about shellfish?

• For as wisdom grows, vexation grows To
  increase learning is to increase heartache.
• Ecclesiastes, 1 18

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Vertebrates Fish
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TBT causes masculinization in fish
TBT (ng/L)
Fish exposed to TBT from hatch for 70 days
McAllister Kime, 2003
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TBT effects on Danio rerio
Control
1 ng/L
100 ng/L
McAllister Kime, 2003
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In human cells, TBT inhibits P450 aromatase
expression
Saitoh et al., 2001
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and activity!
Saitoh et al., 2001
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As a result, there are less female hormones
produced
Saitoh et al., 2001
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EPA Major steps for setting criteria for TBT in
water

• Standard chronic and acute toxicity tests
• LC50 or EC50 ? Final Acute Value
• Chronic toxicity limits ? Final Chronic Value
  (0.0658 ?g/L for saltwater)
• Weight of Evidence Considerations
• Lowering criteria if sound scientific evidence
  indicates that adverse effects may be expected on
  important species
• Imposex in snails at lower TBT concentrations
  than FCV
• Bioaccumulation and bioconcentration
• Immune effects in oysters

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Current EPA water quality criteria for TBT

• Based on Section 304 (a) (1) of Clean Water Act
• Freshwater standards (not to be exceeded more
  than once in 3 years)
• Chronic 0.072 ?g/L (4-day averages)
• Acute 0.46 ?g/L (hourly averages)
• Saltwater standards (not to be exceeded more than
  once in 3 years)
• Chronic 0.0074 ?g/L (4-day averages)
• Acute 0.42 ?g/L (hourly averages)

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Are there environment-friendly alternatives to
TBT?
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TBT good old antifouling paints
www.ortepa.org
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Self-polishing resins Better coats for more
controlled release
www.ortepa.org
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Alternative solutions Silicon-based foul release
coating
www.dt.navy.mil
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Foul release coating systems
www.dt.navy.mil
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How Does Fouling Happen?
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Australian red seaweed, Delisea pulchra
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Bacterial Abundance onCo-occurring Seaweeds
Sargassum sp. Delisea pulchra
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Inhibition of Pigment in Chromobacterium violaceum
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Halogenated Furanones
Halogenated furanones from Delisea pulchra
Acylated homoserine lactones
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Furanones Penetrate Biofilms, Prevent Signalling
and Cause Detachment
no addition
5 µg/ml C56
10 µg/ml C56
Day 1
Day 4
Day 6
Day 10
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Does This Actually Work?
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Field trial, furanones in polymers ( 5 months)
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Advantages of furanones

• Non-toxic to humans and aquatic wildlife
• Does not persist in the environment
• No possibility of resistance development
• Low effective does (µg/L)
• Can be incorporated into polymers (plastics and
  paints)
• Water soluble
• Cost effective

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Other Uses

• New class of antibiotics
• Use in contact lens and catheters