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Report on tributyltin.

Report on tributyltin.

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  • 1.                  Pollutants  Chemistry    Tributyltin  compounds                            Joel  Emmanuel  Bortoni-­‐González  June  11th,  2013      
  • 2. Introduction       Tributyltin  (TBT),  (C4H9)3Sn,  is  a  chemical  used  mostly  in  biocides  in  the  form  of  other   compounds   like   tributyltin   hydride,   (C4H9)3SnH,   and   tributyltin   oxide,   C24H54OSn2,  due  to  the  fact  that  TBT  by  itself  is  unstable  and  will  break  down  unless  combined.  It  is  part  of   the   aromatic   hydrocarbon   chemical   family.   These   types   of   hydrocarbons   have  alternating  double  and  single  bonds  between  carbon  atoms  forming  rings,  like  benzene  in  Figure  1.  The  term  aromatic  has  nothing  to  do  with  the  physical  property  of  aromaticity,  a  chemical  property  that  describes  the  way  in  which  a  conjugated  ring  of  unsaturated  bonds,  lone  pairs  or  empty  orbitals  exhibit  a  stabilization  stronger  than  would  be  expected  by  the  stabilization   of   conjugation   alone,   but   rather   to   the   fact   that   these   chemical   compounds  have  a  scent,  sweet  in  most  cases.      Figure  1.  Benzene  model  where  the  circle  denotes  the  alternating  double  and  single  bonds  between  carbon  atoms.       The  most  common  TBT  compound  is  the  tributyltin  oxide  (TBTO)  and  has  been  the  subject  of  most  TBT  tests.  This  compound  and  other  eight  TBT  compounds  are  referred  to  as  organotins.  Characteristics       TBT  compounds  are  liquids  often  colorless,  unlike  TBTO  that  tends  to  have  a  slightly  yellow  color,  and  have  an  odor  similar  to  gasoline.  TBTO  is  insoluble  in  water  due  to  the  fact   that   they   react,   but   is   soluble   in   hexane   and   most   organic   solvents   (ethanol,   ether,  halogenated   hydrocarbons,   etcetera)   and   is   flammable   but   does   not   form   explosive  mixtures   with   air.   Its   melting   point   is   located   around   53ºC   and   its   boiling   point   around  193ºC  and  it  has  a  density  of  1.103  g/ml  at  20ºC.  It  breaks  down  slowly  in  the  presence  of  oxygen,  light  or  heat.  Prominent  uses       TBTO  is  an  effective  biocidal  preservative  for  wood,  cotton  textiles,  paper  and  paints  and  stains  for  residential  homes.  Mainly,  it  is  added  as  an  antifouling  agent  in  numerous  formulations  of  marine  paints  and  boat  hulls,  docks,  fishnets  and  buoys  to  discourage  the  growth  of  marine  organisms  such  as  barnacles,  bacteria,  tubeworms,  mussels  and  algae.  
  • 3. Quality  regulations       Most   of   the   international   regulations   on   TBTO   derived   from   previous   cases   of  imposex  on  several  snail  species  in  France  and  Great  Britain.  Nowadays  regulations  tend  to  decrease  the  use  of  TBT  based  antifoulings.  In  1987  a  Europe-­‐wide  ban  of  its  use  on  boats  of   under   25   meters   long   was   established.   In   the   United   Kingdom   the   use   of   TBT   based  paints  continues  on  larger  vessels  and  it  remains  at  present  the  most  effective  means  of  controlling  fouling.  In  November  1998  the  International  Maritime  Organization  made  the  decision  to  introduce  a  worldwide  ban  of  the  use  of  TBT  in  antifouling  paints  for  most  ships  from  January  2003,  a  ban  that  has  been  in  place  for  several  years  mainly  in  countries  with  a  lot  of  maritime  activity,  such  as  Japan.  Pressure  for  a  complete  ban  of  TBT  in  antifouling  paints  has  been  increasing  due  to  evidence  that  it  is  bio-­‐accumulating  in  food  chains,  with  particularly  high  levels  being  found  in  marine  mammals.  Toxicity       Since  TBTO  is  used  mostly  on  products  that  will  be  in  touch  with  water  studies  of  the  effects  of  TBTO  products  on  living  organisms  have  been  primarily  performed  on  aquatic  life.   Effects   of   TBT   products   on   humans   are   not   clear,   but   several   incidents   of   human  exposure   to   the   biocide   have   been   reported:   underwear   treated   with   TBT   has   caused  severe   skin   irritation   to   its   wearer,   shipyard   workers   exposed   to   TBT   dust   and   vapors  developed  breathing  problems,  irritated  skin,  headaches,  colds,  flu,  fatigue  dizziness  and  stomach   ache.   TBT   exposure   can   also   irritate   the   eye   and   mucous   membranes   and  prolonged  exposure  may  cause  liver  and  kidney  damage.  M  &  T  Chemicals,  one  of  the  main  producers  of  TBTO,  claim  that  workers  exposed  to  this  substance  metabolize  it  within  3  days.     Single   exposure   of   TBTO   on   rats   demonstrated   a   transient   increase   in   adrenal  weight  shortly  after  exposure  and  a  transient  effect  on  thyroid  follicles;  these  effects  are  reversible.   Inhalation   studies   of   a   single   4   hours   exposure   of   rats   to   aerosols   of   TBTO  showed  irritation  and  enteritis.  Studies  where  10  male  and  10  female  rats  were  exposed  to  saturated  gases  of  TBTO  didnt  show  any  death  occurring  during  exposure  for  7  hours  or  in  the  following  14  days  observation  period.  Short  term  exposure  of  TBTO  on  10  male  and  10  female  rats  involving  repeated  inhalation  in  "nose  only"  chambers  during  4  hours  5  days  per  week  produced  sever  toxic  effects,  inflammatory  reactions  in  the  total  respiratory  tract  and  histological  changes  in  the  lymphatic  organs  were  observed;  5  males  and  6  females  died  during  this  study.     In   mammals,   high   levels   of   TBTO   can   affect   the   endocrine   glands,   upsetting   the  hormone  levels  in  the  pituitary,  gonad  and  thyroid  glands.  Large  doses  of  TBT  have  been  shown  to  damage  the  reproductive  and  central  nervous  systems,  bone  structure  and  the  gastrointestinal   track   of   mammals.   A   large   number   of   studies   have   been   conducted  showing   that   TBTO   causes   depression   of   immune   functions   dependant   on   the   thymus.  These  effects  occur  at  doses  lower  than  those  that  cause  other  toxicity;  the  critical  effect  for  TBTO  is  immunotoxicity.  
  • 4.   Cancer   assessment   has   been   conducted   in   rats   and   mice   following   oral   exposure.  Increases  in  benign  pituitary  tumors,  in  pheochromocytomas  and  in  parathyroid  tumors  at  the  highest  dose  tested  were  shown.  It  is  unclear  if  TBTO  is  responsible  for  these  tumors  since  the  strain  of  rats  used  they  normally  occur  with  variable  incidence.  The  mice  didnt  show  any  sign  of  a  tumor  due  to  TBTO.    Eco  toxicity       Much   of   the   concern   of   the   use   of   tributyltin   stems   from   its   use   as   a   marine  antifoulent  in  paints.  This  compound  is  slowly  released  from  the  paint  on  the  hull  of  the  boat   into   the   adjoining   water   hindering   the   growth   and   attachment   of   a   variety   of  organisms   to   the   boat.   Consequently,   tributyltin   concentrations   in   harbors   and   bays   in  Great  Britain,  France  and  the  United  States  were  high  enough  to  significantly  affect  oyster  and  mussel  production.  Imposex,  the  development  of  male  characteristics  in  females,  has  been  initiated  by  TBT  exposure  in  several  snail  species.  In  laboratory  tests,  reproduction  was  inhibited  when  female  snails  exposed  to  50  ppt  of  TBT  developed  male  characteristics,  such  as  male  genitalia.  Imposex  was  also  noted  in  the  mud  snail  at  less  that  3  ppt  of  TBT.     TBT   is   extremely   toxic   to   crustaceans.   Lobster   larvae   show   a   nearly   complete  decrease   in   growth   at   just   1   ppb   of   TBT.   Molluscs,   used   as   indicators   of   TBT   pollution  because  of  their  high  sensitivity  to  those  chemicals,  react  adversely  to  very  low  levels  of  TBT  (0.06-­‐2.3  ppb  of  TBT).  They  release  TBT  very  slowly  from  their  bodies  after  it  has  been  absorbed.   TBT   toxicity   in   the   field   may   be   substantially   underestimated   in   laboratory  studies.   TBT   binds   to   the   sides   of   containers   and   plankton,   which   contributes   to   this  underestimation   of   its   potential   toxicity.   Generally,   the   larvae   of   any   tested   species   are  more  sensitive  of  tributyltin  exposure  than  the  adults.     Some  fish  can  degrade  TBT  due  to  special  enzymes  that  these  fishes  contain.  In  the  Chinook   salmon,   once   absorbed   it   breaks   down   into   di-­‐n-­‐butyltin   (DBT).   Rainbow   trout  eggs  are  killed  between  10-­‐12  days  of  TBT  exposure  at  5  ppb.  At  lower  levels  no  deaths  occurred,   but   blood   and   liver   metabolism   changes   were   noticed.   Growth   reduction   and  liver  changes  also  occurred  in  young  trout  exposed  to  lower  levels  of  tributyltin  chloride.  Also,  after  seven  days  of  low  level  TBTO,  the  corneal  membranes  of  the  rainbow  trouts  eyes  were  destroyed.  TBTO  has  been  shown  to  inhibit  cell  survival  of  marine  unicellular  algae  at  very  low  concentrations.  Pollution  in  Arcachon  Bay  and  beginning  of  the  ban  on  its  use       Until  the  mid  1970s,  Arcachon  Bay  had  been  an  important  area  for  oyster  culture,  with  production  of  10,000-­‐15,000  tons  per  year,  covering  substantial  areas  of  the  tidal  mud  flats.  The  bay  was  also  popular  with  leisure  craft,  with  vessels  numbers  increasing  from  7,500  in  the  mid  1970s  to  15,000  at  the  start  of  the  1980s.  Estimated  inputs  of  TBT  to  the  bay  peaked  at  around  8  kg  per  day.  Imposex  was  first  observed  in  the  bay  in  1970,  affecting  the   predator   oyster   drill,   leading   rapidly   to   its   near   extirpation   from   the   bay.   TBT   was  identified  as  the  responsible  agent  only  in  the  early  1980s.  
  • 5.   Had  the  adverse  effects  been  limited  to  the  loss  of  this  species,  considered  a  pest  within  the  shellfish  industry  for  its  damage  of  oyster  stocks,  little  if  any  action  may  have  followed.   However,   this   early   warning   was   followed   by   failure   of   the   oyster   stocks  themselves.   Despite   a   normal   spawning   event   in   the   summer   of   1976,   few   of   the   larvae  survived.   Larval   settlement   largely   failed   through   the   late   1970s   and   into   the   1980s,  resulting  in  massive  financial  losses  by  the  shellfish  industry.  By  1981,  oyster  production  had   fallen   to   only   3,000   tons.   In   addition   to   reproductive   failure,   adult   oysters   were  rendered  unsaleable  by  shell  deformation  leading,  in  sever  cases,  to  ball  shaped  specimens.       Such   observations   predated   analytical   techniques   sensitive   enough   to   describe   in  detail   environmental   distributions   of   TBT.   In   1986   the   first   survey   of   organotins   in   the  waters   of   Archon   Bay   was   provided,   while   sediments   data   were   not   available   until   the  1990s.   Nevertheless,   the   severity   of   impacts   on   the   ecology   of   Archon   Bay,   manifest   in  heavy   financial   losses,   was   sufficient   to   stimulate   relatively   swift   action   by   the   French  government.   Acting   on   the   best   information   available   linking   the   oyster   collapse   to   the  presence  of  TBT  paints  to  small  vessels  (less  than  25  meters  long)  in  1982,  beginning  the  ban  on  said  boats.  These  controls  undoubtedly  markedly  reduced  TBT  inputs  to  marinas  throughout   France.   In   the   case   of   Arcachon,   implementation   was   probably   aided   by   the  local  provenance  of  many  boat  owners  and  their  interest  in  preserving  a  local  industry.    Sources    Concise  International  Chemical  Assessment  Document  14:  Tributyltin  Oxide.  -­‐  Dr.  Robert  Benson;  World  Health  Organization.  Tributyltin.   -­‐   Extension   Toxicology   Network.   Retrieved   from:  http://pmep.cce.cornell.edu/profiles/extoxnet/pyrethrins-­‐ziram/tributyltin-­‐ext.html    Tributyltin   (TBT)   antifoulants:   a   tale   of   ships,   snails   and   imposex.   -­‐   David   Santillo,   Paul  Johnston  and  William  J.  Langston.  Tributyltin  pollution  on  a  global  scale.  An  overview  of  relevant  and  recent  search:  impacts  and  issues.  -­‐  Dr.  Simon  Walmsley;  World  Wildlife  Fund.