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Toxic Effects. Toxic Effects. Artificially produced organometallic compounds. Biotransformation of arsenic in marine ecosystems: natural production of organometallic compounds. Organometallic compounds. Definition of organometallic compounds: constituting an organic compound
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Artificially producedorganometallic compounds Biotransformation of arsenic in marine ecosystems: natural production of organometallic compounds Organometallic compounds Definition of organometallic compounds: constituting an organic compound containing a metal, especially a compound in which a metal atom is bonded directly to a carbon atom.
Organometallic compounds Tributyltin compounds (TBT’s) have entered the marine environment as a result of their use in anti-fouling paints on boats and aquaculture equipment. They are manufactured compounds that have no counterpart in nature. The friction caused between the hull of a ship and the water causes ‘drag’ which can affect fuel consumption. This drag effect is increased by the growth of marine organisms and plants on the ship’s hull known as ‘fouling’. As a ship typically only enters dry dock every two to five years for cleaning, an alternative approach to reduce fouling is the application of anti-fouling paints. These coatings inhibit the growth of marine organisms through the controlled release of biocides. The most common and effective chemical used to date has been tributyl tin. They came into use in all classes of shipping in the 1970’s and were subsequently used to treat net enclosures of mariculture installations and wooden lobster pots. Due to its broad-spectrum toxicity, TBT is also used as a fungicide, bactericide and as an insecticide on textiles, paper, leather and electrical equipment. TBT compounds were initially used as they were more effective and longer-lasting than mercury or copper-based antifouling paints. The organic form of the metal is more toxic than the inorganic form due to the greater ease of uptake by organisms.
Organometallic compounds The fate of TBT in the environment TBT is bioaccumulated by fish, crabs and micro-organisms. The chemical half-life of TBT in harbour water is approximately one week and is thought to be controlled by biological uptake and subsequent degradation. Degradation rates are slower in the sediment (months to years) than in the water column (days to weeks) although concentrations of TBT are higher in marine sediment. It is suggested that this may be due to the inhibitory effect of higher TBT concentrations on bacterial activity. TBT is generally degraded by bacteria into dibutyltin (DBT) and monobutyltin (MBT) which are less toxic forms of their parent compound.
Organometallic compounds Endocrine Effects Of Tributyltin Compounds Since the early eighties the development of male sexual characteristics (the so-called imposex condition) has been reported for females of some marine neogastropod snails. This phenomenon has been primarily attributed to the contamination of coastal areas with tributyltin (TBT). Species inhabiting rocky shores, as well as soft bottoms of peripheral seas, are reported to be affected. The mechanism of toxicity in snailsis described as a result of increased testosterone level in treated female snails. Some scientists postulated TBT inhibition of Cytochrome-P450-aromatase, which normally metabolizes testosterone to 17 bb-estradiol in females. An alternative hypothesis is neurotoxic effects of TBT resulting in increased testosterone production in female snails. Based on the published studies, a hormonal (androgen) effect of TBT is assumed in this group of marine snails. The effect is definitively concentration dependent. On the basis of an extensive two-generation study with snails , it was be demonstrated that imposex is induced in adult, female N. lapillus at TBT concentrations below 2 ng/L.
Example - Pacific Oyster TBT also has sublethal effects which are detrimental to local shellfisheries. These compounds may cause reduced growth rates and other effects to young Pacific oysters (Crassostrea gigas ). TBT causes a thickening of the oyster shells and a large reduction in meat content. The effect is due to an enzyme disfunction in shell deposition and results in making the oysters unmarketable. Oysters affected in this way are often referred to as “golf-ball oyster”. A) Normal oyster, about 8 years old B) Oyster with first 5 years of growth affected by TBT, followed by 3 years after TBT ban; C) Oyster, exposed to high levels of TBT throughout 8 years of life Organometallic compounds The Severity of the Pollutant and its Effects TBT compounds have been described by scientists as being amongst the most toxic compounds ever produced and are therefore lethal to a wide variety of planktonic organisms. TBT compounds are known to have affected at least 72 species of gastropod mollusc world-wide. They affect planktonic mollusc larvae which are 10-1000 times more sensitive than the adult molluscs. Initially, carnivorous neogastropods (such as whelks) were found to be affected but more recently other herbivorous gastropods (whelks on rocky shores) have been affected.
Organometallic compounds The ecotoxicological impact of TBT on fish, birds seals and other marine mammals has been less well studied. TBT has however been shown to have an endocrine disruptive effect in fish, birds and mammals. As organotins (e.g. TBT) are bioaccumulative in certain marine species, some of which are consumed by humans, there is justifiable concern over the level of exposure to humans. Butyltin compounds including TBT, DBT and MBT have been detected in almost all marine mammal liver samples from all around the world. This illustrates the world-wide distribution of organotins in the oceans. Concentrations of TBT are greatest in coastal waters especially around developed countries. It is thought that TBT is moderately to slightly toxic to mammals. Some mammals such as the sea lion have the ability to degrade or expel butyltins from their body, whilst others, such as dolphins, exhibit age-dependent biomagnification of butyltins. High doses of organotins have been shown to damage the central nervous system and reproductive mechanisms in mammals. It is therefore likely that organotins are being passed to humans consuming marine mammals as a significant proportion of dietary protein and fat intake. The specific effects of TBT on humans, however, are still not that clear.
Organometallic compounds As the environmental effects of TBT became known in the 1980’s, governments around the world introduced legislation to tackle the problem. In July 1987, the UK Government banned the use of TBT-based antifouling paints for vessels under 25m in length and also its use in aquaculture. The use of TBT on ocean-going vessels is still permitted on the grounds that these vessels do not sit for long periods of time in near-shore waters and are therefore unlikely to affect local shellfisheries. However, through the International Maritime Organisation, a ban on the application of TBT came into force on the 1st January 2003, with a complete global prohibition by 1st January 2008. Other compounds can be used in anti-fouling paints as an alternative to TBT e.g. copper- and mercury-based compounds however these are not as effective or long-lasting as paints with associated TBT compounds present. In addition, the impact on the environment of these alternative anti-fouling paints may not be fully understood. Other alternatives exist such as polysiloxane silicone polymers and epoxy urethane coatings. These methods create a slippery surface from which micro-organisms are washed off when water flow rates exceed approximately 2m/s.
Radioactive compounds Radioactivity Atoms are either stable or radioactive. The nucleus of a stable atom does not change in form over time. A radioactive isotope (radioisotope) has an unstable nucleus. In 1980, Choppin and Ryberg stated in their book Nuclear Chemistry , "We can conclude that nuclear stability is favored by even numbers of protons and neutrons." *Therefore, it is the ratio of neutrons to protons that determines the stability of an atom. Stability for light elements exists when the number of protons to neutrons is about equal. However, for heavier atoms, the nucleus is stable when the ratio of neutrons to protons is from 1 to 1.5. *Choppin, G.R. and Ryberg, J. Nuclear Chemistry: Theory and Applications. New York: Pergamon Press, 1980. Plot of the number of neutrons versus the number of protons in stable nuclei. As the atomic number increases, the neutron-to-proton ratio of the stable nuclei increases. The stable nuclei are located in the shaded area of the graph known as the belt of stability. The majority of radioactive nuclei occur outside this belt. All nuclei with 84 or more protons (atomic number 84) are radioactive .
Radioactive compounds Radioactivity A radioactive nucleus undergoes change by emitting different forms of radiation, either particles or photons. (A photon is a "particle of light" that produces electromagnetic radiation.) These changes are known as radioactive decay, and the phenomenon is known as radioactivity. Through radioactive decay, the unstable nucleus is rearranged to become more stable, until the proton-to-neutron ratio falls within the belt of stability. The basic unit of measure for radioactivity is the number of atomic decays per unit time. In the SI system, it is the Becquerel (Bq), defined as one decay per second. An older measure is the curie (1 Ci = 3.7x1010 Bq). The units used to describe the dose or energy absorbed by a material exposed to radiation, are dependent upon the type of radiation and the material. X-ray or g-radiation absorbed by air is measured in Roentgens (R ). The dose absorbed by any material, by any radiation, is measured in rad (1 rad = 100 erg/g with 1 erg = 10-7 J of absorbed energy). The SI equivalent is the gray (1 Gy = 100 rad). The historical unit to describe biological damage is rem (roentgen-equivalent-man) and the SI unit is sievert (1 Sv = 100 rem).
Radioactive compounds Radiations from radioactivity There are three types of radiations corresponding to three types of radioactivity. alpha radioactivity corresponds to the emission of a helium nucleus, a particularly stable structure consisting of two protons and two neutrons, called an a particle. beta radioactivity corresponds to the transformation, in the nucleus: - either of a neutron into a proton, beta -radioactivity, characterised by the emission of an electron e- - or of a proton into a neutron, beta +radioactivity, characterised by the emission of an anti-electron or positron e+. It only appears in artificial radioactive nuclei produced by nuclear reactions. gamma radioactivity , unlike the other two, is not related to a transmutation of the nucleus. It results in the emission, by the nucleus, of an electromagnetic radiation, like visible light or X-rays, but more energetic. gamma radioactivity can occur by itself or together with alpha or beta radioactivity.
Nuclear fusion (a thermonuclear reaction ) is a process in which two nuclei join, forming a larger nucleus and releasing energy . Nuclear fusion is the energy source which causes stars to shine, and hydrogen bombs to explode. U fission chain reaction: along with barium and krypton, three neutrons are released during the fission process. These neutrons can hit further U-235 atoms and split them, releasing yet more neutrons. Radioactive compounds Radioactivity Two other phenomena, nuclear fusionand nuclear fission, involve fusing and splitting nuclei, respectively. Fusion occurs naturally on the stars. Fission occurs, for the most part, in a nuclear reactor and (on rare occasions) in natural deposits of heavy elements.
Radioactive compounds Half-Life Radioactivity can be described in terms of half-life. The term was coined by Ernest Rutherford. A half-life is defined as the amount of time required for one-half of the atoms of a radioactive substance to decay into another form. For example, if you have one pound of an isotope of polonium-210 and the half-life is 138 days, after 138 days, only a half pound of the original amount remains; after 276 days, only one-fourth of the original isotope is left. The polonium-210 has changed (decayed) into atoms of lead-206. Only one-eighth will remain after 414 days and one-sixteenth after 552 days. Every radioisotope has a characteristic half-life. This amount of time varies from millionths of a second to billions of years, depending upon the particular isotope.
Radioactive compounds The following tables give examples of some well-known radioisotopes, the type of radiation emitted, and their half-lives.
Radioactive compounds Half-Life Biological molecules contain significant amounts of carbon, including both carbon-12 and carbon-14 isotopes. The age of biological material can be determined based on the carbon-14 decay rate. Since the half-life of carbon is relatively long, this method can only be applied to objects from a few hundred to 50,000 years old. Carbon-14 is incorporated into our body tissues due to the amount of carbon-14 in our food. The intake of carbon-14 stops when we die. The approximate age of an individual organism can be estimated if the ratio of carbon-14 to carbon-12 is known in a similar organism today.
Radioactive compounds Natural radioactivity and its distribution The exposure to natural sources is caused by two different sources: A. Cosmic radiation that impacts on the Earth, and its intensity depends on geographical positions on the Earth. B. Natural radionuclides that are normally present in the environment. These nuclides can be divided into three groups according to their origin: Cosmogenic nuclides that are generated by the nuclear reactions during the interaction between cosmic radiation and stable isotopes, especially in the atmosphere (for example, a well-known 14C isotope is generated by the reaction 14N(n,p) --> 14C ). The original primordial nuclides that originated in the early stages of the universe are even now present on the Earth due to their long half-lives (>108 years) in a significant quantity (e.g. 238U, 235U, 232Th, 40K, 87Rb etc.). Many other nuclides that were early generated decayed due to their short half-lives, and these isotopes are not detectable any more.
Radioactive compounds The original radionuclides disintegrate to the secondary radionuclides and form the decay series. There are four well-known decay series, i.e., uranium-radium decay chain (starting from 238 U), thorium decay chain (starting from 232 Th), actinium decay chain (starting from 235 U), and neptunium decay chain (starting from 237 Np). The last two groups of natural radionuclides originate from the Earth, and these are called " terrestrial ". From the point of view of human exposure, only some natural radionuclides are important. The external exposure is mainly caused by 226 Ra (or by uranium), 232 Th and 40 K which can be found in rocks and soil on the earth's surface (the thickness of the layer is some few tens of centimetres). The dose rate that originates from terrestrial nuclides is about 0.057 mGy/hr, (this is the mean value on the Earth), the maximum values have been measured on monazite sand in Guarapari, Brazil (up to 50 mGy/hr and in Kerala, India (about 2 mGy/hr), and on rocks with a high radium concentration in Ramsar, Iran (from 1 to 10 mGy/hr). From the point of view of internal exposure , radon ( 222 Rn), thoron ( 220 Rn), and their decay products prevail.
Radioactive compounds Natural radioactivity and its danger to humans Nowadays, fear of the population of radioactivity is focused on artificial radiation sources, especially on nuclear facilities. Most people do not suspect that the greatest exposure to the population is caused by natural sources. Human bodies have been always exposed to natural radiation, and to a certain extent, this exposure has been unavoidable. Some groups of the population on the Earth are exposed to radiation doses that are by one to two orders higher than the global mean value of radiation doses. It is surprising that attention has been devoted since the turn of the 1980s to the highest exposures to the population that are caused by indoor radon. In some houses in the Czech Republic, radon concentrations that entered from the soil were as high as the ten times the value of the limit value of the radon concentrations in uranium mines, and the annual doses of the population were more than a hundred times higher than the dose mean value in the population.
Radioactive compounds Some natural radiation sources are affected by human activities, and it is reasonable to control them. The examples are as follow: remedial measures during the construction of new buildings or the reconstruction of the existing buildings; remedial measures to reduce the exposure to the population from underground water sources with the higher concentration of natural radionuclides; and control of the natural radionuclides released to the environment during industrial activities. From the point of view of internal exposure, potassium 40K. is also a significant nuclide. The potassium concentration in the human body is nearly stablein all persons at a level of about 55 Bq/kg, which corresponds to the annual effective dose of 0.17 mSv. Because of internal exposure, attention should be devoted to the following isotopes: radium 226 Ra and 228 Ra, uranium 238 U and 234 U, polonium 210 Po and lead 210 Pb. The great differences may appear in nuclide uptake (and also in corresponding doses) for individual persons or the groups of the population. With the exception of the inhalation of radon and its decay daughters that contribute to the highest doses to the population, the uptake by ingestion, in general, is much higher than that by inhalation. From the point of view of the exposure to population, the contribution of the cosmogenic nuclides (not cosmic radiation) is negligible.
Radioactive compounds Humans are exposed every day to radioactive elements that occur naturally in the environment. Gamma and alpha radiation emitted by radioactive elements in rocks and soils, especially those that decay quickly (such as radon), pose a health risk. This radiation is implicated in cancers of the lung, bone, and of other organs. The health threat posed by uranium alone primarily as a heavy-metal chemical poison similar to arsenic. This is known as chemotoxicity and is implicated in kidney disease. Radon is especially dangerous because it is a gas and can easily enter the lungs. Although natural concentrations of these radioactive materials are usually less than established threshold health values, human activity often inadvertently exposes us to radionuclides at dangerous levels. The Environmental Protection Agency (EPA) estimates that as much as 30 percent of the public drinking-water supply in the United States exceeds their recently-established maximum contaminant levels for radon. An even greater percentage of private water supplies, unregulated by EPA, may contain elevated levels of radioactive materials.
Radioactive compounds Radionuclides are present in all rocks in varying amounts, and they are easily mobilized in the environment. The high geochemical mobility of radionuclides in the environment allows them to move easily and to contaminate much of the environment with which humans come in contact. Uranium, in particular, is easily mobilized in ground water and surface water. As a result, uranium and its decay product, radium, enter the food chain through irrigation waters, and enter the water supply through ground-water wells and surface-water streams and rivers. The health risks to humans are real, but the level of risk involved is not clearly defined because we do not yet know enough about the distribution and concentration of these radionuclides. Uranium frequently and preferentially concentrates in wetland environments where uranium-rich rocks occur. Concentrations of uranium in dead and decaying organic material in wetlands is a potential threat to the health of humans and to wetland habitats. Although many wetlands serve as natural filters protecting surface waters from uranium contamination, disturbances of wetlands from such events as hurricanes, dredging, draining, road building, and water recovery, may allow uranium to become mobile, contaminating water which is subsequently consumed by humans and other animals.
Radioactive compounds Uranium contaminates surface waters in many irrigated lands. In irrigated areas along the Arkansas River Valley in southeastern Colorado, uranium and salts are actively leached from marine shales. These contaminated, saline, irrigation waters eventually return to the river where uranium levels increase to concentrations as high as 200 parts per billion and, because of the accompanying high salinity, wetlands in this area are not trapping uranium. In other much-publicized wetland areas such as the Kesterson Wildlife Refuge in California, uranium and selenium contamination is responsible for wildlife death and deformities. Many other irrigation systems in semi arid areas that drain farmland on marine shales face similar stresses on water quality. Uranium in surface waters of the Arkansas River Valley, SE Colorado, April 1991. Irrigation waters taken from the upstream parts of the river are used to flood fields where they leach uranium and salts from the rock and soils. Much of this water is then returned to the tributary streams and the main river.
Radioactive compounds The geochemistry of uranium. Dissolved uranium complexes in water with dissolved fluorides, phosphates, and carbonates. When phosphate precipitates from water uranium goes with it. As a result, for example, uranium is a serious contaminant in phosphate fertilizers that are ubiquitous in crop farming. As irrigation water containing uranium is used, fertilizers that also contain uranium serve to compound the potential toxicity. Although most crops resist uptake of radioactive materials in their leafy (above-ground) components, those crops whose roots are consumed (such as potatoes, peanuts, carrots), are susceptible to contamination by uranium. Geochemical sampling and detailed geological mapping are essential early steps to knowing where irrigation water, contaminated by underlying rocks or by fertilizers may be a problem.
Radioactive compounds HLW = high-level waste
Log time (years) Radioactive compounds
Radioactive compounds The global dispersion and deposition of debris from atmospheric nuclear weapons is by far the largest source of artificial radioactivity released into the global environment.
Radioactive compounds The injection and partitioning of radioactive debris in the atmosphere can be estimated from the location and yield of each test. The total fission energy is largely divided between the equatorial Pacific (43%) and the polar North (43%).
Radioactive compounds Other important sources of artificial radioactivity in the marine environment include the dumping of neclear waste, effluent discharges form nuclear jule cycle and nuclear weapons production, accidental relases from land-based nucelar installations, and other accidents and losses at sea involving nuclear matearial.
