tirsdag den 24. maj 2011

AFS: substances with hormone-like effect

Tri-butyl tin (TBT) is a term for a range of chemical substances that all have the structure of tri-n-butyltin, which is quadrivalent tin with three covalently bound n-butyl groups. The last free space on the tin atom (Sn Atomic Signs by name stannum, atomnr. 50) can either be absorbed by an anion or a second organic compound. AFS has a very strong toxic effect, and this is exploited when it fought fouling of various organisms (bonded algae, barnacles, mussels, etc..). However, the substance beyond its direct toxic purpose other adverse ecological effects, the causes for frequent genital changes in many snails.

When TBT degrades in the marine environment, it happens in a stepwise demerger of each butylgrupperne via di-butyltin and monobutyltin to inorganic tin. If it does not decompose directly it will bind to various organic molecules, and thus sink and become deposits of TBT-containing sediments, and here is the breakdown very slowly. And examines in this, we find out that the biological half-life or biodegradation as it is called, so dependent on the amount of oxygen present (as there generally is not much oxygen at the bottom). And this causes the AFS not being degraded to the less toxic di-butyltin and monobutyltin. The actual breakdown is primarily done in bundsedimentet and I could imagine that it was a biological degradation by bacteria and fungi as the primary reasons for this I am with that biodegradation, abiotic Otherwise, as a rule is the main form of degradation. That TBT is not degraded in the sediment could produce the conclusion that it is not as harmful as it easily absorbed by marine organisms if it is free in the water, but concludes that this ignores an important detail, namely that this goes beyond the particular types of snails and mussels are just living on the organic base material such as whelk do. Another factor that makes AFS additional problem arises as a result of his surroundings, is the residue in ports which are likely to be very large. And just in ports is an artificial damming of ocean currents and swells, which causes further that there is no mixing in water, and thus no oxygen present. It may also be mentioned that different animals are not equally quick to demolish the same substances. I could well imagine that clams and other molluscs (Mollusca), which is a very ancient family of organisms that are not particularly good at the breakdown, as it could be made that involve a number of unique enzymes.

When toxic substances, including TBT released from the boat sides, it has both some direct and some indirect impact on the environment. The direct effects are damage to cells, species and communities in the water and seabed. Generally, do damage to plant and dyreplanktonets species richness and species composition. But another, more or less indirect, effect of these de-TBT, as previously mentioned gender changes with different shells (in our case Konk-snail Buccinum undatum). One must assume that this process is irreversible, so that the phenomenon developed as a very specific response to TBT pollution, and that change does not go back to the stage before the contamination by the absence of TBT. Looking at the graph you see a level indicator up the second axis, where 0 is normal females, and 6 is the climax stage with blocked ægleder, pseudo-penis and Vas deferens, representing a qualitative scale. And out along the first axis, we have the quantity of TBT per. liter of seawater. In addition, one can see that there really is not much more than one nanogram, representing a billionth of a gram, per AFS. liters of seawater to cause development of male sex characteristics in hunsneglene. (which tells us that whelk is Gonochorism unlike many other snails), this indicates that TBT is an incredibly strong poison. And you can even see that virtually all the observed snails (if I counted correctly it was about 25 pcs.) Reaches level 5-6 after only 5 ng. The graph rises quickly at first, then flattens out asymptotically.

When whelk hit by this kind of imposex, namely the formation of male sex characteristics, primarily the penis and the Vas deferens, also called pseudotvekønnethed as they developed genitals can not be used for propagation, it must immediately due to TBT has endocrine disrupting effects. Either it works directly as male sex hormones, or increases the production of the snail its own, and in the manner of the oppressed female sex hormones, so that there are developed a penis and Vas deferens. Woven from these agencies goes directly into and blocking æglederen and cause therefore that the snail is sterile and that the eggs can not be separated from æglederen. If one must compare the elements of TBT and testosterone (the primary male sex hormone), one must look at what groups the molecule is composed and see if there are no striking similarities and immediately I can see no striking similarities, because testosterone is primarily composed of cyclical low, and it possesses none of the AFS. Contrast similar to AFS more cholesterol, but in addition to steroid cholesterol is the building block for the synthesis of testosterone, I can not see any clear link. Yet we must conclude that there is a part of the TBT molecule that can bind to testosterone receptors and thus affect hormone balance, or otherwise create an imbalance. However, one can imagine that whelk not have testosterone but another sex hormone, which could also explain the lack of apparent similarities.

As a starting point antifoulant AFS is not intended as an endocrine disrupter. It is designed to have a toxic effect on organisms which fastens at the bottom of ships, the substance must therefore have a second and more direct, and even more effective way to beat the organisms killed, either by destroying their respiration, immune system or other vital. Generally one can say that even just TBT specifically target organisms as a part of their lives living freely in water, and a second part takes cognizance of solid objects (the underside of a ship), it will have a major impact on the entire marine ecosystem, and in each context are closely linked in a larger chain. From the smallest ultra plankton on to pico-, nano-, micro, mesoplankton which are eaten by small fish larvae, which are eaten by larger predators, which in turn are eaten by them in the top of the Danish marine food chain, namely porpoises Phocoenidae sp. And other fish birds (cormorant Phalacrocoracidae sp., gull Laridae sp. etc.) This is also evident from Figure 3, showing various sea animals concentration of butyltin, measured as ng tin / g dry weight. And here it appears that the higher up the food chain we go, the greater the content of the substance. They say TBT bioaccumulate, in brief: a mussel living by filtering the water of organic material, which here contain TBT, it is to eat a lot of organic material to recover its energy needs (it is estimated a ratio of 1:10, ie. a tipotens through each step in the food chain (mathematically it can be signed 10 x, where x represents the number the food chain, as in our example would be 4)), so this will be eaten by flounder, which in turn will eat a lot of clams. Until we get to the top of the food chain where porpoises are and this is so not only eaten fish, but with the fish eating animals lower down the food chain, it has actually eaten a large mass of organic material. Why animals can not excrete the substance indicates that the substance is fat-soluble, hydrofobt, since these substances are more difficult to be separated, but are typically stored in liver and adipose tissue.

Besides all showed effects of TBT have on the marine environment, it also has an effect on people. Since we are ultimately in the top of the sea, as well as all others, food chain, we will eat many marine creatures such as oysters, mussels, flounder, etc. (maybe not exactly whelk, eider ducks or guinea pig), and thus we will obtain large quantities of TBT into the body, and AFS is indeed portrayed as a poison for living cells, so close to the same cells found in the human body. Has the substance in sufficient quantities it can also go in and disrupt the hormonal balance, as is the case with whelk.

A plasmid is an independent, ring-shaped DNA molecule which is not linked to a chromosome. Plasmid found mainly in bacteria (Prokaryotae). Plasmid can be transferred more or less controlled from bacteria to bacteria which is the reason for resistance to many different substances such as various pesticides and antibiotics has been spreading very rapidly (see drawing at left). It is this cellular characteristic capitalizing. Man is able to insert different plasmids in the cell (yeast Saccharomycetaceae), and this splits as a multiple, and all the new cells will, like the parent cell, contain the two inmates plasmids: a plasmid encoding the human estrogen receptor (as yeast cells do not contain estrogen receptors). And another coding for an enzyme marker. The first plasmid will operate just as if it were the cell's own genetic material, ie. it will make protein synthesis, and make the protein the gene codes for addition, in our case will be produced in the human estrogen receptor, which will be transported into the cytoplasm, as it would in human cells.

If a substance possessing hormone-like properties, it has far reaching consequences. A key aspect is that different substances which might previously have been rubber-stamped, can simulate the properties of the hormone, or go and inhibit their functions, thus directly or indirectly create havoc in the so well-adjusted hormone balance. In our everyday lives where we are constantly surrounded by thousands of chemicals, ranging from the cellophane packages we our food into, the shampoo we wash our hair with, it is essential to identify these compounds and clarify their effects so that consumer can be aware of the health risks associated with the product and ultimately to ban the harmful substances. It previously did the hormone-like substances difficult to identify is that the effect is often manifested in offspring later life, such as may be reflected in the poor sperm quality, impotence, hermaphroditism (will be detected immediately), infertility, cryptorchidism, hypospadias , testicular mm. The reason it is especially important to examine whether a hormone-like substance in the marine environment is that there are no physical barriers to migration of a substance in this medium. In other words, we in Denmark can be low enough restrictions on the use of TBT in marine paints, but that countries such as Poland and other Baltic countries which have borders with the Baltic Sea, may not have the same strict requirements for environmental protection. Their pollution can affect us. Humans can absorb TBT and other butyltin compounds from fish, mussels and other food from the sea. And I could imagine that the seas around Denmark are particularly busy, just because land is relatively small, and we have a high traffic of both the before mentioned countries. In addition, the average depth quite low. It will say there is little water compared to the large volume of both crossing. Another disadvantage of TBT and other hormone-like substances in the maritime environment is the fact that pollution is not a point source pollution, as it often would be on land (for example, would a local release of toxic substances, may be relatively simple to define), but a surface contamination . The substance can be said as freely floating around, and therefore makes the purification of the substances in the ocean impossible. And if its degradation phase is very slow, the consequences of previous year's unrestrained use of the given substance only continue, although a possible ban on the substance would occur.