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CASPIAN SEA ENVIRONMENTS 311 POCs; proportions and content of POCs in river waters compared with maximum permissible concentration (MPC, for DDT, HCH and PCB, are equal to 100, 20 and 1 ppb correspondingly for water and 100, 100 and 100 for bottom sediments); behavior oftoxiccompoundsinthewaterbody;factorspromotinganincreaseoftheecological risk of polluted riverine input into the Caspian Sea (Figure 4). The interactions of POCs with oil-products and synthetic surfactants in river and marine waters are considered, as well as secondary contamination of waters by POCs from bottom sediments. The “black box” principle was applied to estimating the ecological risk of toxic compounds contamination. 3.1. DDT and HCH Insecticides ThewholeproductionofDDTwasapproximately4.5milliontonsfrom1950to1970 and it is used today in some regions (Zakharenko and Mel’nikov, 1996). The environ-mentalbehaviorofDDT,HCHandotherpesticidesischaracterizedbypartialremoval from the soil with surface runoff and discharge of toxic compounds into the rivers (Galiulin, 1999). Land erosion plays the most important role for soil particles with the adsorbed POCs to enter surface waters (Vrochinskii and Makovskii, 1979). The most intensive removal of pesticide residues occurs in the irrigated agrolandscapes with surface and drainage runoff. Usually the content of pesticides in the drainage discharge is higher than that in the receiving waters. At present, the main source of surface water pollution by DDT and HCH insec-ticides may be related to their loss or leaching from the contaminated regional soils where these chemicals were used to protect agricultural crops and perennial plants from various pests and diseases. These insecticides were stored and accumulated in soils due to their high persistence, forming so-called “regional pedogeochemical anomalies (RPA)” characterized by increased toxic compound content as compared with regional background (Galiulin, 1999). According to Bobovnikova et al. (1980), the loss of DDT and HCH residues from the soil surface is relatively small, annu-ally about 0.1–1.0% from the soil pool. This is an evidence of long-term period for insecticide residues entering into surface waters. ThehighercontentofDDTmetabolites(DDE+DDD)comparedwithDDTitself (i.e., (DDE +DDD)/DDT >1) in surface waters indicates a high degree of microbial transformation of the initial compound in the soil. The DDE and DDD are formed by DDTdehydrochlorinationanddechlorination,respectively.Onthewholeitmeansthat loss or leaching of toxic compounds take place from RPA formed some decades ago. It is known that HCH preparation is as the eight isomers mixture (α, β, γ, δ, etc.), and therefore the detection of two and more of its isomers in water testifies on its regional usage (Figure 5). A detection of β-isomer HCH in water in relatively larger quantities in compari-son with other isomers shows a high degree of insecticide transformation in the soil (mainly by microorganisms), and hence loss or leaching of insecticide residues de-positedsomedecadesago.Itisknownthatβ-isomerHCHisthemoststablecompound among others of HCH isomers, i.e., it is not or very weakly exposed to elimination reaction—dehydrochlorination (Cristol, 1947). High persistence of HCH β-isomer is 312 CHAPTER 16 Figure 5. Isomers of HCH. Orientation of chlorine atoms in molecules of different isomers of HCH. α—aaeeee; β—eeeeee; γ—aaaeee; δ—aeeeee; ε—aeeaee; ξ—aaeaee; η—aeaaee; θ—aeaeee (Mel’nikov, 1974). connected with its chlorine atoms, equatorial conformation, which provides the most energetically favorable configuration of the substance (Chessells et al., 1988). The detection of DDT in surface waters as (DDE + DDD)/DDT < 1 reflects mi-nor transformation of the initial insecticide in the soil and hence the toxicants loss or leaching from recently formed RPA or so-called local pedogeochemical anomalies, LPA (former action zone of plants for DDT preparations production; places of acci-dental spillage or output of the preparations; areas of storage or burial—tombs, etc. thatarecharacterizedbyextremelyhighcontaminationlevel(Lunev,1997;Silowiecki et al., 1998). Meanwhile,thedetectionofα-orγ-isomerHCHinrelativelyhighconcentrations when compared with other isomers suggest relatively little transformation of HCH or lindane, which are known to include up to 70% of α-isomer and no less than 99% of γ-isomer, respectively. On the whole this would suggest a loss or leaching from recently formed RPA or LPA. ThemonitoredproportionsofDDT((DDE+DDD)/DDT>1or<1),HCH(β > α,β > γ,β > δ, etc.; α > β,α > γ,α > δ, etc.) and lindane (γ > α,γ > β,γ > δ,etc.)maybeconsideredforinterpretingtheirbehavior,inparticular,transformation in bottom sediments as an accumulating compartment of an aquatic ecosystem. The pesticide residues entering receiving waters are transported as water soluble, adsorbed on suspended particles and colloidal forms. Here, they are subjected to different processes like deposition, volatilization, hydrolysis, microbiological and photochemical transformation (Mel’nikov et al., 1977; Vrochinskii and Makovskii, 1979; Allan, 1994). According to Komarovskii et al. (1981), in running water the deposition of DDT and HCH to bottom sediments is minimal. Another situation is observed at slow current when the vast silting zones begin to form and the movement of water masses along the riverbed is hampered or stopped. Under these conditions the pesticide residues, being absorbed to suspended particles, are removed from the water mass and, due to sedimentation, precipitate and accumulate on the bottom. Shcherbakov(1981)hasalsoconcludedthataccumulationofresidualDDTandHCH in the bottom sediments of reservoirs was strongly affected by the velocity of the water current and the type of sediment. In flowing water bodies, the pesticides are CASPIAN SEA ENVIRONMENTS 313 removed almost completely near the river mouth. Therefore, their residual amounts are minor in the places of entry, where the current velocity is higher. This fact allows us to explain the non-uniform distribution of organochlorinated pesticides in bottom sediments of reservoirs. The content of pesticides in the sandy sediments is lower than that in the silted ones, and much lower compared to the clay sediments. Bottom sediments in water bodies accumulate various toxic compounds due to theirhighadsorptionrateontheparticlesurface(thisvarieswithparticletype)andlow temperature of the bottom layer, which reduces the transformation rates. The largest amount of toxic compounds is accumulated in the subsurface silt or clay layers with anaerobicconditions(Rheeetal.,1989).AtpresentahundredthousandstonsofPOCs have been “stored” in the bottom sediments, and their continued input into the water column adds to present contamination (Afanasiev et al., 1989). Persistent organochlorinated pesticides entering with surface discharge into a wa-terbodymayenterintothebiogeochemicalfoodwebofaquaticecosystems:water → bottom sediments → invertebrates → vertebrates (Shcherbakov, 1981; Bashkin, 2003). In contaminated fresh and salt waters, pesticides are prone to bioaccumulation in bottom sediments, water plants, phyto- and zooplankton, and benthic organisms, fishandotheraquaticorganisms,andeventuallymaybetransferredviathefoodchain to humans. For example, Komarovskii et al. (1981) showed that distribution of DDT between the elements of biota occurred according to the principle of biological inten-sification,i.e.,oneorderofmagnitudehigherconcentrationineverylinkofthetrophic (food) chain in accordance to biomagnification. The increase of concentration is dis-tinctlyobservedbythevalueofaccumulationcoefficientsofinsecticideresiduesinthe trophic chains: “zooplankton–planktonivorous fishes–piscivorous fishes–mammals– silt–zoobentos–bentosivorous fishes”. The simplest model used in aquatic ecosystems is based on the simplified food chain: water → fish or mussel → fish or mussel eating birds/mammals. Assuming that the mammals or birds feed on fish or mussels, the simplest model to calculate an MPC based on this food web is: MPCwater = NOECspecies of concern/BCFfood species of concern where:MPCwater isMaximumPermissibleConcentrationofachemicalinwater,ppb; NOECspecies of concern is No Observed Effect Concentration of the food (invertebrate) corrected for the species of concern (mammals or birds, ppb); BCFfood species of concern is Bioconcentration Factor, representing the ratio between the concentration in the invertebrate, being the food of the species of concern, and the concentration in water. A simplified scheme of a POC’s transformation in a biogeochemical food web in an aquatic ecosystem is shown in Figure 6. Histologicalresearchesshowedthatpersistentorganochlorinatedpesticidesfound infishorganshadexertedapolytrophicaction,i.e.,affectedthecentralnervoussystem, 314 CHAPTER 16 Figure 6. Simplified scheme of a POC’s transformation in a biogeochemical food web in an aquatic ecosystem. I—receptor, II—compartment. liver, gills, kidneys, spleen and digestion tract (Shcherbakov, 1981). Changes of fish organsmanifestedfromminordisorderofbloodcirculationanddystrophicchangesup to formation of necrosis and necrotic centers. Accumulated in gonads the pesticides affect not only the individual, but also their offspring. This may facilitate various lethal and chronic effects, such as lethal mutations deformity, stop the processes of individual evolution, provoke mortality at the early stages of the caviar development, and lead to the birth of nonviable youth (Braginskii, 1972). Meanwhile, in Russia and Kazakhstan the complete absence of DDT and HCH isomersresiduesisrequiredforwaterofthefishfarmingwaterbodies(Afanasievetal., 1989; Korotova et al., 1998). An acute toxic effect of DDT and HCH insecticides and other organochlorinated preparations on the most sensitive organisms ranges within concentrations of 0.001–1,000,000 ppb (Braginskii, 1972). Such high sensitivity to these concentrations is determined, on the one hand, by extraordinary toxicity of the substances, and on the other hand, by specific character of their effect on vitally important functions, which is common for insects and many water animals. The toxicity range is wide: they easily affect many representatives of Arthropoda, in particular Crustacea, which are the major part of sea and fresh water zooplankton. Therefore, the concentration of pesticides found in water deserves comparison with the so-called toxic quantities for organisms or NOEC values. 3.2. Substances for Industrial Use—PCBs PCBs represent chlorine derivatives of biphenyl, containing from 1 to 10 atoms of chlorineinamoleculethatisexpressedas10differenthomologues(Figure2).Having noethanebridgebetweenthearomaticrings,asopposedtoDDT,PCBsaremorestable CASPIAN SEA ENVIRONMENTS 315 in the environment (Surnina and Tarasov, 1992). According to the data of Samson et al. (1990), the T50 value of highly chlorinated PCBs can be up to a few decades. The main source of environmental pollution with PCBs is industrial and waste inputs. PCBs enter into the environment due to the leakage from transformers, con-densers, heat exchangers or hydraulic systems, leaching and evaporation from differ-ent technical devices, disposal of liquid waste waters, as well as owing to application of PCBs as filler for pesticide preparations (Tyteliyan and Lashneva, 1988). The direct disposal from ships of used hydraulic liquids and greases is of local impor-tance. From 35% (Surnina and Tarasov, 1992) to 80% (Tuteliyan and Lashneva, 1988; Bunce, 1994) of global PCB production was discarded into the environment with other wastes. Meanwhile a great part of these toxic compounds entered into sur-face and marine waters. In recent decades 1.1–1.2 million tons of these preparations have been globally produced (Surnina and Tarasov, 1992; Amend and Lederman, 1992). The contamination of bottom sediments in the world reservoirs, including a number of Volga river reservoirs, by PCBs is higher than by persistent organochlo-rinated pesticides (Afanasiev et al., 1991; Khadjibaeva et al., 1996). Both PCBs and organochlorinated pesticides are transported in water-soluble form, adsorbed on the particles and colloidal forms (Allan, 1994). The water organisms enable accumu-lation of PCBs, and their concentrations in algae, plankton and fish are positively correlated with concentrations in bottom sediments (Tuteliyan and Lashneva, 1988). A single contamination of silts by PCBs may result in constant local uptake by water organisms for a long time (up to several years), once the incident has occurred. The effect of PCBs, for example, on fish has a cumulative character and their toxicity increases with decreasing degree of chlorination of the compound (Polychlorinated, 1980; Bashkin, 2003a). It should be noted that in Russia PCBs are not allowed in water of fish farming water bodies (Ecological Herald of Russia, 2002). 3.3. Other Factors Increasing POCS Environmental Risk Interaction of POCs with Oil-Products and Synthetic Surfactants The oil-products (fuel, petrol oils and solvents, illuminating kerosene, etc.) and syn-theticsurfactantsinriverwatersenteringtheCaspianSeamayinteractwithPOCsand enhance the toxic effect of these compounds. It is known that synthetic surfactants are used in production of detergents, pesticides and also oil-processing and petro-chemical industries. Therefore synthetic surfactants may increase the ecological risk of contamination by POCs. Organochlorinated insecticides, brought into the sea as suspended particles by the rivers, can be dissolved in oil-products of contaminated seawaters. These combined pollutants can suppress photosynthesis of phytoplankton byupto95%,underconcentrationsofabout1μg/l.Thisleadstoadecreaseofprimary production in vast areas of the sea (Braginskii, 1972). The following mechanism may be suggested. The formation of POCs–oil complexes will be inevitably accompanied by decreasing photosynthetic re-aeration and weakening oxidative function of water plants,oneofthemainfactorsofself-purificationofreservoirfrompetrolcontamina-tion.Ontheotherhand,thecomplexofunsaturatedcompoundsandoil-products(like ... - tailieumienphi.vn
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