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c. Chlorinated Dibenzofurans Another group of halogenated hydrocarbons that has received considerable attention in recent years because of the multiple impacts of the contaminants on aquatic organisms includes the chlorinated dibenzo-p-dioxins (CDDs) and chlorinated dibenzofurans (CXDFs). These aromatic heterocyclic compounds appear to be highly toxic to marine organisms, and they can induce serious sublethal effects. Occurring as trace contaminants in organic chemicals, such as chlorinated phenols, PCBS, and phenoxy herbicides. CDDs and CDfs enter estuarine and marine environments via wastewater discharges, groundwater inflow, sewer overflows, storms drains, and atmospheric deposition. CDDS and CDFs are widely distributed in seawater and sediments at low parts-per-trillion concentrations. Being environmentally persistent and highly lipophilic compounds, CCDs and CDFs tend to bioaccumulate in marine organisms by food chain transfer rather than by direct uptake from seawater, suspended matter, or bottom sediments. d. Effects on Biotic Communities Halogenated hydrocarbons pose a potentially serious threat to the structure of estuarine and marine communities because some species, particularly those occupying upper tropic levels, accumulate the contaminants to very high levels and, hence, are susceptible to chronic chemical exposure. The high mortalities of harbor seals, together with diminished hatching success of marine birds exposed to DDT and PCBS, provide examples. Field investigations will continue to be extremely difficult to conduct because a single sample collected at an impacted site may contain as many as 100-150 different halogenated hydrocarbon compounds. 2. Heavy Metals a. Composition and Sources One of the less desirable by-products of an industrialized society is the increase of heavy metal accumulation in marine environments. Heavy metals may be grouped into two categories: 1. Transitional metals: Transitional metals (e.g. copper, cobalt, iron, and manganese) include those elements essential for metabolic function of organisms at low concentrations but may be toxic at high concentrations. 2. Metalloids: (e.g., arsenic, cadmium, lead, mercury, selenium, and tin) are generally not required for metabolic activity but may be toxic at low concentrations. Estuarine and oceanic waters receive heavy metals from both natural and anthropogenic sources. Natural processes (e.g., weathering and erosion of rocks, leaching of soils, eruption of volcanoes, and emissions of deep-sea hydrothermal vents). Anthropogenic inputs are usually much greater in coastal waters near urban or industrialized centers. b. Metal Toxicity Heavy metals are toxic to marine organisms. The approximate order of increasing toxicity of heavy metals, according to Abel,79 is a s follows: Co, Al, Cr, Pb, Ni, Zn, Cu, Cd, and Hg. However, the toxicity of a given metal varies in estuarine and marine organisms for several reasons : (1) The capacity of the organisms to take up, store, remove, or detoxify heavy metals differs considerably. (2) Many intrinsic and extrinsic factors influence heavy metal uptake: intra and inter-specifically variable intrinsic factors, such as surface impermeability, nutritional state, stage of molt cycle, and throughout of water by osmotic flux. (3) Extrinsic physico-chemical factors, such as dissolved metal concentration, temperature, salinity, presence or absence of chelating agents, and presence or absence of other metals. Once assimilated by marine organisms, heavy metals may be sequestered by metallothioneins and lysosomes, thus facilitating detoxification processes. Metal binding activity of metallothioneins and lysosomes is also variable in marine organisms. The toxicity of trace metals has been coupled to the free metal ionic activity regardless of the total metal concentrations. In marine environments, heavy metals occur in dissolved form (as free ions, complexes ions, etc.) or in the solid state (as colloids, adsorbed onto particle surfaces, in mineral matrices, etc.) They may be present as inorganic and organic species. At toxic levels, heavy metals act as enzyme inhibitors in marine organisms. They also adverse affect cell membranes. Organometallic species often damage reproductive and central nervous systems. Other disruptions include changes in physiology and development. Feeding behavior, digestive efficiency, and respiratory metabolism commonly are adversely affected. a. Metal Concentration i. Copper The levels of copper in estuarine waters (-0.2 to > 100 µg) are usually much greater than those in oceanic waters (~0.1 µg/1) because dissolved copper sorbs to particulate matter, the concentrations in bottom sediments can be a substantial. A positive correlation exists between the concentrations of copper in sediments and those observed in many benthic species. ii. Cadmium The concentrations of cadmium in coastal waters removed from industrialized centers range from 1-100 ng/1. Where inputs are elevated because of industrial or municipal waster disposal. Cadium accumulates in bottom sediments at, cadmium concentrations generally range from 0.1-10.0 µg/g, dry wt. Mussels (Mytilus spp.) used as sentinel organisms in coastal regions have accumulated cadmium to mean levels of 1-5 µg/g dry wt. iii. Lead The concentrations of lead in the open ocean range from 0.0010.014 µg/1. Lead levels in estuaries and coastal marine waters exceed those in the open ocean by a factor of 10 or more. Organ lead compounds are generally more toxic to marine organisms than inorganic forms. The amount of lead in marine mammals (i.e., dolphins, porpoises, seals, and whales) from waters around the British Isles is 0.05 – 7.0 µg/g wet wt.2 Mercury Mercury in marine environments include elemental mercury, divalent mercury ions (Hg2+), and methyl mercury ((CH3)2Hg). Mercury readily sorbs to particulate matter and tends to accumulate in bottom sediments. Most of the mercury accumulating in shellfish (40-90%) and finish (>90%) is methyl mercury. The levels of mercury in marine mammals (i.e., dolphins, porpoises, and seals) generally are between 03 and 430.0 µg/wet wt. iv. Tin Inorganic tin concentrations in open ocean waters vary from 0.003-0.008 µg/1. Localized elevated levels of dissolved tin, approaching 50 µg/1, have been documented in coastal waters receiving industrial discharges. Marine invertebrates can accumulate significant levels of tin Effects on Biotic Communities. Dissolved copper concentration of 1-10 µg/1 have been shown in the laboratory to increase mortality of young bay scallops, species diversity of benthic faunal communities in Norwegian fjords showed a strong negative correlation with copper concentrations in bottom sediments. Even at extremely low levels, cadmium may adversely affect benthic organisms. A negative correlation between bacterial biomass and cadmium concentrations in the northern Tyrrhenian Sea, with high cadmium concentrations possibly arresting bacterial development. Plankton populations are also very sensitive to cadmium. The toxicity of inorganic lead to marine organisms is less than that of may other heavy metals. Under experimental conditions, marine organisms display adverse effects of inorganic lead only when concentrations are about 100 times greater than those in coastal waters. The presence of organo-tin compounds in marine waters has assumed increasing significance in recent years in regard to impacts on biotic communities. When exposed to tributyltin (TBT) concentrations as low as 0.01 µg/1, marine invertebrates often exhibit changes in growth and reproduction. Oyster shell abnormalities, reduced growth rates in mussels, imposex in stenoglossan gastropods, failure of recruitment in clams, and breakdown of sexual differentiation and failure of settlement in oysters have all been linked to TBT exposure (Table 23). Organotins can be magnified to relatively high proportions in invertebrates (commonly >60%). Food chain magnification of TBT does not appear to occur in higher organisms (i.e., crustaceans, fish, and mammals), however, because they possess the necessary enzymes to break down the contaminant relatively rapidly. TBT is extremely toxic to many marine organisms; it is not very stable and degrades to less toxic compounds in a few weeks in marine, environments. 7. Radioactivity a. Sources i. Natural Sources Radionuclides in estuarine and marine environments derive from both natural and anthropogenic sources (Tables 24-26). Natural background radiation is attributable to cosmogenic and primordial radionuclies. Cosmogenic radionuclides originate from the interaction of primary cosmic rays with matter in the atmosphere and on the surface of the earth. The collision of high energy particles (cosmic radiation) with nitrogen, oxygen, argon, and other atoms in the upper atmosphere produces secondary particles, primarily neutrons and protons. Secondary cosmic radiation accounts for nearly all cosmic rays impinging on the sea surface. Primordial radio nuclides are those that were generated at the time of formation of the earth. ii. Anthropogenic Sources Since 1944, artificial radioactivity has entered estuarine and marine environments from several major anthropogenic sources, namely nuclear weapons testing. The relative importance of these anthropogenic sources of radionuclide has changed over the past 50 years. Between 1945 and 1980, most artificial radionuclide entering the sea originated from nuclear weapons testing. More than 1200 nuclear weapons tests were conducted throughout the world during these 35 years, with the major bomb testing programs conducted between 1954 and 1962. After the Partial Nuclear Test Ban Treaty of 1963, underground nuclear weapons testing became most important, and atmospheric weapons fallout to the sea diminished substantially. Atmospheric fallout of radionuclides from nuclear weapons testing has been about four times greater in the northern hemisphere than in the southern hemisphere. A number of fission products of nuclear detonations in the atmosphere are biologically significant in the sea, notably carbon (14C), cesium (137Cs), strontium(89Sr, 90Sr), and iodine (131I) isotopes. Anthropogenic sources of radioactive materials in the sea have become important, particularly those associated with the nuclear fuel cycle. Radioactive waste is produced at various stages of the nuclear fuel cycle (i.e., mining, milling, conversion, isotopic enrichment, fuel element fabrication, reactor operation, and fuel reprocessing) (Figure 14). Major accidents at nuclear power plants, such as at the Three Mile Island in Pennsylvania and Chernobyl in the Ukraine, release considerable activity that may be detected in seawater samples. In the case of Chernobyl, radio sink levels in muscle of fish fro the southern Baltic Sea increased three- to four-fold, and Cs, 134 Cs, and 137 106 Ru in fish in the Danube River increased five-fold. The disposal of radioactive materials in the sea has been restricted to low level wastes released via discharges from landbased sources or direct dumping of packaged wastes.