Stephen Karafiath
Material Science p. 5
Toxic Materials Report
 

A problem that has long plagued engineers is how to manufacture paint for the hulls of ships that will keep barnacles and other organisms off of the hull while being environmentally friendly and staying cost effective. In the past, designers opted to use tributyl tin in paint because with its biocidal properties it kills barnacles and other organisms that would otherwise remain attached to the boat. However, it was discovered that Tributyl tin not only kills organisms in direct contact with the boat but is also lethal to other marine organisms as it seeps out of the paint. This discovery led certain nations such as Australia, France, The United States, and others to ban Tributyl tin starting around 1980. However, Tributyl tine is still widely used on large ocean-going vessels so trace amounts of tributyl tin are found in almost every harbor.

According to OSHA, the main classification of Tributyl tin has many subgroups which include all of the following:

Tributyltin Fluoride

Dibutyltin Dilaurate

Tributyltin Benzoate

Dibutyltin Maleate

Stannous-2-Ethyl Hexanoate

Butyltin Trichloride

Bis(Tributyltin) Oxide

Triphenyltin Hydroxide

Tin Mercaptide;

Tetramethyl Tin

All of these materials have been shown to cause symptoms such as Headaches, vertigo; eye irritation; psycho-neurological disturbance; sore throat, coughing; abdominal pain, vomiting; urine retention; paresis; focal anesthesia; skin burns and pruritis in humans and in animals it can cause hemolysis and hepatic necrosis(OSHA). While it takes a relatively large amount of Tributyl tin to cause such symptoms in humans, it only takes trace amounts as small as 50 ng of Tributyl tin to cause problems for Mollusks and other bi-valves. The reason that Mollusks such as clams, oysters, and muscles are so susceptible to the tributyl tin poisoning is because they function as filters to clean the water so even when living in very small amounts of tributyl tin the mollusks filter out the tributyl tin and it builds up inside them. The tributyl tin causes many problems for the mollusks, the foremost being that it weakens and deforms their shells and gives them reproductive difficulty. Even those Mollusks who are still able to reproduce often give birth to Mollusks with birth defects who die soon after they are born. Before Tributyl tin was banned, The oyster populations of many harbors were all but completely wiped out.

One study designed by J.L Sericano was specifically engineered to test the effects of tributyl tin on the American oyster or Crassostrea virginica. This study involved two different groups of oysters, One group from Hanna Reef that is relatively uncontaminated by tributyl tin and one group that was native to the Houston Ship Canal which has higher concentrations of Tributyl tin. The Oysters from the clean location were placed in the Houston Ship canal along with the oysters who had lived there for their whole lives. The total Tributyl tin levels increased from 62ng to 380ng during the 48 days that the oysters were there. After the 48 days were up both groups of oysters were transplanted back to the clean water around Hanna Reef. The oysters that were originally from the uncontaminated area were able to get rid of the unwanted tributyl tin in their systems at a rate almost twice that of the oysters that had grown up in a polluted environment(Sericano).

According to NOAA, Tributyl tin is "an organometallic compound with impressive biocidal activity, which has been used extensively in marine paint formulations to prevent the accumulation of barnacles and slime on boat hulls. Tributyl tin can also be broken down into dibutyl tin an monobutyl tin which are not quite as harmful as tributyl tin but are still dangerous to marine organisms. Up until recently, it has been difficult to ascertain how much tributyl tin was actually being absorbed by mollusks because the equipment that was used to take tissue samples was not nearly sensitive enough. Recently however, tests and studies have been performed which conclusively link tributyl tin to defective oysters(NOAA).

According to Batley, "Modern copolymer paint formulations have an initial high leach rate of TBT which, within days, reaches a standard and constant value of

around 4 ug TBT cm-2 day-1. The half-life of TBT in seawater is around six hours, but it rapidly partitions either to suspended sediments or to the surface microlayer. In sediments its half-life has been estimated at around 3.5 years(Batley). Marine paint is not the only source that causes butyl tins to get into the water. It is also used as a catalyst in the plastics industry and as an algaecide in cooling circuits for boilers. There is still no standard method for determining how much tributyl tin contamination is present because of the extremely small amounts. Batley suggests that "Reaction with sodium borohydride forms volatile hydrides which can be trapped on a

chromatographic column, and separated by thermal desorption, with subsequent detection by quartz furnace atomic absorption spectrometry"(Batley). An alternative to this solution is that "the hydrides can be solvent extracted and determined directly by gas chromatography using electron capture or flame photometric detection"(Batley).

Now that tributyl tin has been banned, strict guidelines have been adopted to insure that the mollusks will thrive. The standard maximum allowable concentration of Tributyl tin is 2 ng per L. It is not uncommon for a shipyard that still has traffic with butyl tin painted hulls to have concentrations as high as 100 ng per L or 50 times the legal limit. In smaller harbors in the absence of large ships, the tributyl tin levels are around 10 ng per L. Fortunately however, the tributyl tin levels have been on the steady decline since it was banned and most harbors either are at or will soon be at the recommended levels.

Due to the ban of tributyl tin, other products have been and are being developed for use on boar hulls. Teqmar Antifoul for instance, contains no tributyl tin or arsenic, but still serves as an antifoulant to keep barnacles and slime off of boats. It still contains toxins but they are harmful only to organisms that are stuck to the boat or other marine structure(Teqmar). The banning of tributyl tin from marine paints has basically shut down the last demand for the material in any quantity . Because it is hazardous and toxic to humans it is not used in any other application of modern life.

http://www.erin.gov.au/portfolio/esd/coast_marine/somer/somer_annex2/bat_txt.html

OSHA Field Definitions http://www.osha-slc.gov/ChemSamp_data/CH_271900.html

Sericano, J.L. "Environmental accumulation and depuration of tributyltin"

Teqmar Antifoul, http://www.nw.com.au/~ysyow/protect/products/teqmar.html

 Witney, E. 1991, TBT in antifouling paints - a Queensland perspective, report no. QI91030, Department of Primary         Industries, Queensland.