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46 increased frequency of particle collisions. Thus, shear currents and small-scale turbulence enhance coagulation rates, and high dilution impedes them. Because increased salt concentrations favor coagulation, the dilution of a freshwater waste, such as sewage sludge, with saltwater probably favors coagulation. The distribution of particle sizes is important, with heterogeneous suspensions coagulating faster than homodisperse ones. How these factors interact in the ocean is poorly understood. Nevertheless, coagulation is important in determining the fate of particles because it can accelerate particle sedimentaion. The prediction of sedimentation patterns by computer models (e.g., Hendricks, 1982; Koh, 1982) depends on information of three kinds: (1) the pattern of ocean currents and turbulent diffusion as described in the previous sections; (2) the mass emission rate of waste; and (3) the frequency distribution of fall velocities of waste particles in seawater. Fall-velocity distributions can readily be measured in settling columns by the pipette method. Waste material is diluted with seawater by a factor calculated for the prototype discharge (Brooks et al., 1982; Wang and Koh, 1982). This standard laboratory technique does not reproduce the proper flocculation effects, primarily because the turbulent shear of ocean water is not present. However, it is clear that settling velocities are increased by flocculation, which should cause the sedimentation pattern to exhibit higher fluxes near the discharge point Sediment Resuspension and Bioturbation, Turbidity Currents Sediment resuspension and bioturbation also play important roles as determinants of sediment characteristics in the vicinity of a discharge. Bottom currents at a discharge site can periodically reach speeds capable of resuspending surface sediments in the water. Such events will destroy the chronology of sediment deposition (by winnowing away or redepositing lighter material on the top), oxygenate surface sediments, release interstitial water, deplete dissolved oxygen in bottom water, enhance remobilization, and gradually transport sludge materials away from a dis- charge point. If a waste discharge point is on the continental slope or in (or near) a submarine canyon, sediments may be removed by occasional density or turbidity currents or even sediment slumps. Such removal can carry sediment deposits to deeper water (generally .
47 considered desirable) but may cause sudden release of fine particles and entrapped trace contaminants to the bottom waters. Bioturbation by burrowing animals (except in anoxic sediments) reduces vertical stratification among sediments, moves particles back to the sediment-water interface, and permits sediment oxygenation and other exchanges with the water column by increasing sediment porosity. Together, resuspension and bioturbation may greatly accelerate the release of contaminants from the sediments and the pore water to overlying waters. Most models do not take account of resuspension or bioturbation, but if these factors could be included, the contaminants would be predicted to be generally more widely dispersed in sediments and water. The primary indicator of resuspension is the distribution of grain size in natural sediments at the sediment-water interface. The smallest sizes remaining at a given place are equal to the largest sizes (with their corresponding fall velocities) that are scoured and carried away by strong currents. Light Scattering and Absorption In the case of near- surface discharge of turbid wastes (like sewage sludge), the transmission of light through the water may be significantly reduced by light scattering and absorption. This causes a decrease in the depth of the photic zone. The reduction in light transmissions can be measured in the laboratory with mixtures of waste and seawater at appropriate dilutions. Volatilization Volatilization represents the transfer of volatile chemicals from the water to the atmosphere. To be important in a waste discharge to the coastal sea, particulate and dissolved chemical species must be trans- formed into dissolved, nonassociated chemical species in which the concentration gradient between water and air favors water-to-air transport. Resistance to mass transfer occurs in both the liquid and gas films or on either side of the air-water interface. For most hydrophobic chemical species, resistance to transfer occurs in the liquid phase. Waste disposal that occurs below the thermocline may not allow chemical species to contact the upper mixed zone and to participate in air-water interactions. Waste discharges at depth do not result in losses of volatile components to the atmosphere unless there is significant vertical mixing.
48 2.2.2.2 Chemical Processes The distribution of chemical constituents in a wastefield is determined by the method of discharge and the initial dilution described above in the section on Initial Dilution under Section 2.2.2.1. The initial ambient concentration (CO) of any substance (after rapid dilution but before chemical changes are considered) is given by C0 = Cb + (CW - Cb)/(S + 1), where Cb = background concentration; Cw = concentration in waste stream; S = initial dilution, as parts of seawater per part of waste. The chemical and biological processes discussed below (as well as the physical processes already discussed) cause concentrations and fluxes to change over space and time. Sorption/Desorption The sorption of inorganic and organic components on particles depends on the properties of sorbent, sorbate, and solution: · Sorbent: concentration, surface area, organic carbon content, lipid content, surface properties, particle size, exchange capacity, composition. · Sorbate: concentration, polarity, inorganic versus organic, charge, molecular (ionic) size. · Solution: pa, temperature, ionic strength, total cation and anion concentrations of specific components. For inorganic components (e.g., metals), sorption depends mostly on particle surface charge and area, on speciation in solution, and on concentrations of competing ions. Ion-exchange processes at the solid-solution interface also determine sorption of many inorganic species. For hydrophobic organic compounds, the surface area and organic carbon content of the particles, and the aqueous solubility of the organic component of interest, are probably the most important properties. Desorption of chemical species depends on the same factors.
so results in a precipitate Fe(OH)3(s) that can scavenge metals, organics, and silica from the water. Organisms have the ability to catalyze many chemical transformations. Microbiological catalysis of the oxygenation of manganese (II) to manganese (IV) leads to the precipitation of MnO2(s). Both thermodynamic and kinetic effects govern redox processes in ocean waters. Significant factors include the concentrations of oxidized and reduced species in the waste and the ocean waters, pH, ionic strength, dissolved organic substances, particulate materials, temperature, and light. Thermodynamic calculations of the equilibrium state of the ocean system are feasible for some species (see, e.g., Morel et al., 1975). Reaction rates, which are difficult to predict, can vary widely depending on the substances involved and specific chemical conditions at a disposal site. Photodegradation Photodecomposition of organic species in water depends on the sensitivity of a particular species to photolytic transformations and the availability of light having specific spectral properties at depth. Thus, controlling factors in photodegradation include the following: Light spectrum (especially in the ultraviolet) Light intensity Light attenuation at water depth by water absorption, particle reflectance · Sensitivity of organic species to light of specific spectral properties Efficiency and rate of photon transfer Exposure time of specific light properties In general, photoinduced transformations of organic species are important only in the upper reaches of the euphotic zone. The extent to which these reactions are important depends on the partitioning of photosensitive species between particle and dissolved phases and complexation in solution. Complex Formation Complexes, also referred to as chemical species, are compounds consisting of a metal ion bonded to ligands. Speciation changes frequently result when solutions with different chemical compositions are mixed. Thus, the zone of initial mixing of a waste with seawater is a zone in which complex formation and changes
51 in chemical speciation of trace metals and other con- stituents should occur. Because the reactivity or availability to organisms of a dissolved species is dependent on its speciation, the nature, extent, and rates of chemical transformations subsequent to input of a waste are important. For instance, copper is toxic to organisms as the free ion but is essentially unavailable when complexed with chloride, carbonate, or hydroxide, for example. Thermodynamic considerations indicate that - only a small fraction of copper is uncomplexed in uncontaminated seawater. The complexes/speciation as well as the total amount of the input waste material should be known, but this information is frequently not available. The second major zone in which speciation changes should occur is the sediment-water interface. Redox changes cause changes in ligand concentrations across the boundary and thereby cause speciation changes. For instance, a metal might change from being completed with chloride to being complexed with bisulfide, polysulfides, or organic ligands. - ~ Such changes can result in increased mobility of a complex in sedimentary pore waters or a greater likelihood of its being deposited. Because of the difficulty of analysis, few actual measurements have been made of metal speciation in the natural marine environment and almost none where a waste has been injected. There are thermodynamic models that predict how metal speciation may vary in response to changing ligand concentration. Unfortunately, these have not always agreed with each other. Other Chemical Transformations Chemical transformations - (other than those discussed above) include chemical alterations of organic species by hydrolysis reactions in solution. These chemically induced processes can alter organic pesticides having ester groups as part of their functional components. Hydrolysis rates depend on solution properties (pH; temperature; ionic strength; presence of catalysts, e.g., certain metals) and type of organic compound. General acid- or base-catalyzed hydrolysis of organic esters is common in aqueous environ- ments and is somewhat understood. 2.2.2.3 Biological Processes Pathoqen Mortality _ Historically, one of the principal _ concerns in disposing of sewage wastes has been to make
52 sure that bacteria, viruses, and parasites present in the waste do not reinfect people. Control of human exposure to pathogens is accomplished either by disinfection of the waste stream or by discharge of the waste far enough from shore or deep enough to achieve sufficient bacterial (or viral) die-off or sedimentation before possible transport to shore. Chapter 3. Pathogen mortality is discussed in Biodegradation/Biochemical Transformation Organic compounds in the aquatic environment may be biodegraded to carbon dioxide, water, and other compounds or trans- formed to other forms (e.g., DOT to DOE). The biochemical degradation/transformation of organics depends on the concentration of viable bacterial populations having the ability to perform the transformation. In addition, low ambient substrate concentrations, low environmental temperatures, and nonnatural organic structures greatly affect whether organics are transformed. Although microorganisms can be grown in culture to degrade/ transform all or most recalcitrant compounds, low substrate concentration and low temperatures in the aquatic environment make such transformations difficult to assess. Bioconcentration/Bioaccumulation The partitioning of dissolved inorganic (e.g., trace metal) and organic species (e.g., tPCBs) into living organisms is referred to as bioconcentration. Trace elements exhibit a bioconcentration factor (BCF) of 10,000 or even higher, depending on mode of metal uptake, surface properties of the organism, and chemical speciation of the metal. The partitioning of organics into organisms depends on the lipid content of the organism, the water solubility of the organic, and the rate of organic transfer across the membrane surface. BCFs for typical nonionizable organics vary from 103 to 106. BCFS are proportional to the octanol-water partition coefficient (KoW) and inversely related to aqueous solubility. The relationship of KoW to BCF is: log BCF = 0.79 log KoW ~ 0~40 (Veith and Kosian, 1983). For many organisms, we can accurately estimate bioconcentration from knowledge of chemical concentrations (activity) in water and the BCF for organics that enter the organism primarily by par
53 titioning across the membrane surface into the lipid pool. When ingestion of food is the dominant pathway, less success has been achieved in estimating bioconcentration. Photosynthesis and Chemosynthesis Photosynthesis and chemosynthesis are the processes by which organisms take dissolved matter from solution to form particulate biological matter. Substances incorporated into organisms can become more concentrated than in solution. The energy to drive this process comes from light absorption (photosynthesis) or chemical transformations (chemo- synthesis). Because biological material is composed of chemical elements that occur in relatively fixed ratios to each other, biomass production can be controlled by that element which is least available. Of the three major elements of phytoplankton biomass, nitrogen and phosphorus are relatively less abundant in oceanic surface waters than is carbon. AS a result, their availability frequently determines the concentrations and growth rates of phytoplankton. The processes of concentration into biological particles near the surface, the settling of these particles, and subsequent dissolving determine the oceanic distribution of many elements. These range from those depleted at the surface--including such nutrients as nitrogen and phosphorus and such trace metals as copper, cadmium, and zinc--to those substances depleted at depth, such as oxygen. Officer and Ryther (1977) noted that nutrient enrichment of surface waters in the New York Bight caused the production of plant matter at the surface and a subsequent settling of this organic matter to the bottom. The decay of this organic matter was responsible, they suggested, for the depletion of oxygen in near-bottom waters there. The relatively fixed ratio of major chemical elements in organisms makes it possible to relate changes in oxygen, carbon dioxide, nitrogen, and phosphorus concentrations in solution to changes in phytoplankton biomass. The extent to which the approach involving fixed elemental ratios can be extended to estimate biomass concentrations of other elements and compounds is not clear. For some compounds, such as synthetic organics, there are chemical equilibrium relationships that make it possible to predict concentrations in organisms such as phytoplankton. Thus, our knowledge of the extent to which a substance is incorporated in new biological material depends on the material.
55 Incorporation of small particles into large fecal pellets can affect the fate of discharged particulate matter by increasing vertical transport rates. Decreased rate of dissolution may result from decreased area/unit weight rates of the particles. Important questions still unanswered concern how significant this process is for the sedimentation of domestic or industrial waste components. Critical unknowns are the extent to which animal feeders can or will feed on discharged material and the importance of filter-feeding in subsurface waters. 2.2.3 Predictions of Concentrations and Fluxes 2.2.3.1 Basis for Prediction The basis for predicting concentrations and fluxes is mass balance, or material accounting. The mass balance is usually represented by a model or group of models. ~ I_ _ _ _ ~ ~ ~ ~ ~ ~ ~ _ _ J (Model is used here in the broadest sense or the wore ana includes conceptual, mathematical, and physical models.) There are few problems in marine waste disposal for which a single model is adequate. No one model can be univer- sally applicable to the variety of existing wastes, sites, and disposal systems that exist. Rather, the present practice of employing a hierarchy or suite of predictive models will continue. The essential ingredient in the development of the group of models to be used for concentration and flux Predictions is identification of the processes that are important for the various predic- tions. Experience gained from other marine disposal activities and examinations of the chemical, physical, and biological processes may serve as an early screening tool in the identification of appropriate models. Order-of-magnitude analysis using waste, site, and system characteristics and knowledge of processes may further sharpen the focus on the important processes. Numerical models that include components representing the important physical, chemical, and biological processes provide the opportunity to link (mathematically) these processes to yield an integrated response in terms of concentrations and fluxes. Unfortunately, the more complex the model the more difficult it is to gain insight from the model results. Consequently, numerical models may be developed to handle only portions of the predic- tions, and results from one model may be used as input or
56 design guidance for another model. Time and space scales of physical, chemical, and biological processes often provide natural divisions in such modeling. Near-field and far-field models, and local and regional models, are examples of multimodal coupling. Several models have been used in ocean waste disposal assessments to predict concentrations of substances. Transport trajectories and dilutions for the near-field and far-field behavior of buoyant waste discharges can be found from integral models described in Fischer et al. (1979). Koh (1982) has coupled sedimentation effects with the behavior of submerged sewage sludge plumes to predict waste-particle distribution on the ocean bottom in the vicinity of an outfall. Jackson (1982) employed a one-dimensional (vertical) model of transport processes to examine the impact on water-column chemical con- stituents of sludge injection at various depths in the Santa Monica-San Pedro Basin. He combined estimates of horizontally averaged physical transport processes in the basin with oxygen and nitrate demands of sediments and suspended sludge particles to predict vertical concentra- tion distributions of oxygen, nitrate, particulate organic matter, and oxidized organic matter in the water column. Csanady et al. (1979) provided models of large gyre circulation interactions with waste dumping near the surface at the 106-Mile Ocean Waste Disposal Site (Dumpsite 106). 2.2.3.2 Information Needs for Prediction The information needs for physical, chemical, and biological processes have been discussed in the preceding sections. There are, however, additional needs in the assembly of a prediction. The primary requirement is compatibility among the ingredients in the mass balance in terms of time and space scales. That is, chemical processes that have time scales of days should be matched with physical processes, such as transport by residual currents, having comparable scales. The determination of currents averaged over days may involve a different measurement strategy from that required for currents with shorter time scales. This emphasizes the importance of planning the prediction process before undertaking major measurement programs. Examination of the dominant processes may show that the region of interest can be modeled by assuming a one-dimensional geometry. Lumped
57 or spatially integrated versions of connected processes and of substance concentrations are required for the predictions. For example, descriptions of "patchy" processes that are driven by local concentrations must be made compatible, if possible, with a model framework that uses spatially averaged concentrations. Special informa- tion needs regarding boundary conditions for several substances often result from the combination of various processes in a prediction of temporally or spatially averaged concentrations and fluxes. For instance, the prediction of the flux of a substance may require informa- tion on the concentration of the substance and the current at contemporary times. The mix of information needs may change with each different kind of prediction for the same overall problem as a different process becomes the focus of the predic- tion. The prediction of the sedimentation of sludge in the local vicinity of a sludge outfall, for example, will require different kinds of information about physical transport than will a prediction of basinwide oxygen distribution in the water column as the result of the outfall. Formation of a prediction framework thus involves a reconsideration of physical, chemical, and biological processes, with an emphasis on the relationships among them in a context of common time and space scales. 2.3 CASE STUDY: PROPOSED DEEP-OCEAN DISCHARGE OF SEWAGE SLUDGE The preceding sections indicate the existence of a wide range of waste and site characteristics, discharge systems, and physical, chemical, and biological processes Figure 2.1 indicates that an analysis can be made for each pollutant of any given discharge at a particular site. To arrive at an engineering design, we must con- sider a range of sites, discharge techniques, and possibly predischarge treatment to modify the waste. The resulting matrix is huge. In real engineering cases, however, it is quickly found that there are usually only a few critical requirements and analyses that determine the acceptable choices and rule out the unacceptable ones. In other words, when the critical design requirements are satisfied, other require- ments may be met within a large margin. Thus, efforts in data gathering and research can be focused on the critical
58 areas. Experience and engineering judgment are exercised at the beginning in reducing design options and planning oceanographic surveys. This brief case study illustrates the application of the processes and modeling techniques described in Section 2.2. ~ ~ The case chosen is the proposed deep-ocean discharge of sewage sludge by the Orange County Sanitation District through a special outfall pipe terminating at 400-m depth about 12 km off Orange County in southern California. This project is not allowable under current state and federal laws and regulations and has been proposed as an experiment. A comprehensive research plan was prepared by the Environmental Quality Laboratory (EQL) of the California Institute of Technology to study the transport, fate, and effects of the discharge (Brooks et al., 1982). The EQL report gives the basic information currently available on waste characteristics, site characteristics, and the engineering system (open-ended outfall pipe). Although the report describes extensive additional measurement and research needs, there is a sufficient base for the following discussion. This chapter carries the analysis only up to determination of concentrations and fluxes. These results can be used to analyze biological effects. n~uelonment of an ocean disposal option for sewage sludge, as in this case, is iterative. If some effects are predicted or subsequently observed to be unacceptable, the plan will be adjusted or even abandoned. ~ _ ,= _ ~ Adjustments can be made in the characteristics of the waste (more treatment or pretreatment), the site, or the method of discharge. The characteristics of the sludge stream are given in Table 2.1. A 1:1 mixture of sludge and secondary effluent would be discharged from a pipe lying on the bottom 400 m below the ocean's surface. The warm, low-salinity mixture would rise in the denser seawater, mixing with seawater until it forms a sludge-seawater mixture with the density of the surrounding ocean. The height of rise and the initial dilution of this sewage plume vary with the currents. Rise height is expected to range between 50 and 110 m above the bottom and the initial dilution to vary between 450-700:1, seawater: sludge. The values used for this case study are a 50-m rise height and a 500:1 dilution. When the predilution of sludge with effluent is included as part of the dilution process, the initial dilution would be 1000:1.
59 TABLE 2.1 Characteristics of Projected Orange County Sanitation District Sludge Stream Constituent Concentration Mass Emission Rate Volume Total suspended solids Volatile suspended solids Biological oxygen demand Silver Cadmium Chromium Copper Nickel Lead Zinc PCB CHC pesticides . 3eO MOD (11~4 x 10 L/day) 11~500 mg/L 1 e 33 x 10 3 kg/day 7~000 mg/L 1~700 mg/L 0.8 mg/L le 4 mg/L 5. mg/L 16. mg/L 1~5 mg/L 6. mg/L 20. mg/L 50. ug/L 4. PSI/L 73 x 10 3 kg/day 17 x 10 3 kg/day 9 x 103 kg/day 16 x 103 kg/day 62 x 103 kg/day 190 x 103 kg/day 17 x 10 3 kg/day 70 x 10 3 kg/day 240 x 103 kg/day 0.5 kg/day 0.045 kg/day . SOURCE: Brooks et al., 1982. Following plume rise, further mixing occurs as the plume drifts with the current. We expect the motion to be largely horizontal and parallel to local bottom contours. Turbulent diffusion is likely to be slower at those depths than near the surface. If we assume that the horizontal diffusion coefficient at depth is 10 percent of surface values, then, using results from Brooks (1960), turbulent mixing will provide additional dilution by a factor of 2 or 3 within 12 h. 2.3.1 Suspended Solids Direct effects of sludge particles include turbidity in the water column and the formation of deposits on the ocean bed. Pollutants associated with sludge solids include pathogenic organisms and many toxic metals and synthetic organic substances.
62 Bight suggests that 85 percent of the discharged tPCBs cannot be accounted for by sedimentation in the region of the outfalls. It is likely that the water column is a major reservoir for them. Assuming a water residence time of 100 days and a plume thickness of ~40 m would give an average effluent dilution of 24,000:1. Thus, the initial sludge stream concentration of 50,000 ng/L will be diluted far field to a concentration of -2 ug/L. Assuming sedimentation and other removal processes, far-field tPCB concentrations of several nanograms per liter are possible. Of this amount, -70 to 80 percent will be in the dissolved phase because of the low particle concentrations of less than 0.5 mg/L. 2.3.1.2 Dissolved Oxygen/Biochemical Oxygen Demand If we assume that secondary effluent mixed with the sludge stream has negligible biochemical oxygen demand (BOD), then the BOD in the layer due to the sludge discharge would be 1.7 mg/L--(-l mL/L). Turbulent mixing would further reduce this to 0.5-0.7 mg/L within 12 h. Total oxygen consumption given unlimited time might be 50 percent greater, or 2.1 mg/L (1.5 mL/L). The dissolved oxygen (DO) content at those depths has the same approximate magnitude, indicating that local impacts might be significant. Jackson et al. (1979) estimated sludge degradation rates under these temperature conditions as 1 percent/ day. If the ambient oxygen concentration is 0.5 mL/L, total BOD is 1.5 mL/L, and no mixing occurs subsequent to initial dilution, biological degradation would halve the oxygen concentration of the sludge-seawater mixture in 18 days. Particle removal by settling and mixing processes will decrease this impact on oxygen concentrations. On the basis of these calculations, it seems possible that the naturally low ambient DO concentrations will be slightly depressed locally in the diluted sludge field near the discharge point. However, the sludge discharge system will be specifically designed to prevent signifi- cant oxygen depletion by various methods as more pre- discharge oceanographic information becomes available. Among methods of controlling DO depletion are (1) reducing the BOD mass emission rate by digesting the waste-activated sludge component, (2) reducing outfall depth to get the plume into water with more dissolved oxygen, and (3) employing larger predilutions of sludge with effluent.
64 inorganic phosphate, and smaller quantities of organic phosphates. Nitrogen will be in the form of NH3 (or N at), NO3, and organic nitrogen. Upon decomposition/ mineralization of the sludge particles, P and N will be released in biologically available forms. In the Southern California Bight, nutrient concentra- tions are lowest in the surface waters owing to biological utilization, peak at -100- to 300-m depth owing to microbially mediated decomposition of settling particles (see table below), and generally decrease downward to the sediments. Surface Water Middepth Water (0 to 60 m) (100 to 300 m) Nutrient uM uM Phosphate 0.2 2-3 Nitrate ~0 30-40 Ammonia 0.3 0.1 Expected concentrations will be Nutrient Discharge Stream 1:1,000 Wastefield TP 4-12 me 4-12 uM TN 17-43 me 17-43 AM TOC 250-300 me 250-300 uM Thus 1:1,000 of the discharge stream will perhaps double or triple the ambient concentrations at depths of 300 m. Far-field dilutions of an additional factor of 10 to 100 lead to additions much below ambient levels. It is possible that >50 percent of the nutrients in the discharge stream will be in soluble form. Assuming that only 10 percent of the P. N. and OC in the initial sludge stream is deposited in the sediments within the ~100 km2 predicted by Koh (1982), then P. N. and OC fluxes are as follows: TP: 0.1-0.4 g/m2 yr TN: 0.2-0.6 g/m2 yr TOC: 2.5-3.0 g/m2 yr These data should be compared to natural nutrient fluxes to the sediments.
66 seawater. Jackson (1982) calculated the increased metal concentrations in seawater, assuming that the metals are released in proportion to the dissolution of organic matter. Such a calculation has been adapted to the proposed Orange County outfall (Table 2.2). Compared with the uncontaminated levels of cadmium, chromium, copper, lead, nickel, silver, and zinc, sewage disposal will not increase the ambient levels by more than a factor of 3. Further release of metals to seawater could occur from remineralization at the sediment-water interface where organic compounds produced during the degradation of the sedimented organic-rich sludge could complex metals associated with the naturally occurring sedimentary material. These could be either resedimented, diffuse out, or released during sediment resuspension events. Pseudomonas bacteria extracted from Chesapeake Bay sediments have been found to be capable of alkylating tin and may be able to alkylate other metalloids. Such organotins are much more toxic to organisms than is inorganic tin. The extent to which metalloids become alkylated in sludge-rich sediments is not known. Many trace metals have high concentrations in sewage sludge. It is not feasible to monitor all of them through the many possible chemical reactions that can occur after sludge discharge. Judgments must be made as to which metals and metalloids are more likely to affect public health or ecological communities. One possible way to eliminate some metals is to be found by looking at the areas around pre-existing sludge inputs. The Southern California Coastal Water Research Project (1982) has demonstrated that even though concentrations of cadmium, copper, and zinc are elevated in sediments and organisms adjacent to outfalls, the presence of a detoxifying completing agent (metallothionen) in sea urchins and croaker fish enables these species to prevent concen- trations of uncompleted, toxic cadmium, copper, and zinc in their surroundings from entering sensitive cellular sites. In fact, less than 2 percent of the capacity of the metallothionen pool in animals near existing outfalls has been utilized. This has been interpreted as indicating that cadmium, copper, and zinc could be considered nonproblems .
67 U] o .,, a, o o C Pi o o C) · - 1 Sat En Go g a) O A: U] ~5 ~ O ~ W ·,1 sat O hi: .,. 3 o m o U] a, Id o 0 a) P U. - 0 o o w Al ~ W J:: 0 t) 0 U] a ~ ~ g 0 0 0 ~ ~ 0 UD o .,, o Cal o U] ~ ~ a, · - X ~ 0 a ~ 0 it; O or 1 0 o as anon ~ co ~ Do 1 1 1 1 1 1 1 O O O 0 0 0 0 X X X X ~ x kg 0D u~ a~ ~ · c e c c c c kg O O ~1 CO ~1 CO 1 1 1 1 1 1 1 O O O O O O O - 1 ~1 ~1 ~1 ~1 ~1 ~1 X X X X X X U~ ~ L~ C C C C C C C 0o ~ CO ~ U~ O O a, ~ cn _I cc' ~I CO 1 1 1 1 1 1 1 O O O O O O O ~1 ~1 - 1 ~ X X X X X X X U~ ~ O ~ ~ U~ c c c c ~ c c 0h 0 ~ 0D ~ U~ ~ ~C ~ ~mm a) c · - 1 1 1 1 1 1 1t- O ~O O O O O O O - a) ~ ~ ~ ~ ~ ~ ~ ~= ~_ 3 ~X X X X X X X O ~ ~C co ~n e C C C C C C C C C .< ~ O C 1 0 \9 ~ ~ - ·,' O X 0 ~ ~ .. C =-- .- ~ O a, ~ ~ ~ ~ ~ ~ c 0 a) ·- ~ .,' 0 C) O ~ Z U] ~U]
68 2.4 ULTIMATE FATE Present studies of the fate and effects of contaminants rarely extend to-spatial scales larger than several kilometers. Such scales are not always large enough to determine either fate or effects. For example, less than 10 percent of the trace metals that have been discharged from one southern California sewage outfall has been found in nearby sediments (Bering and Abati, 1978; Morel et al., 1975). Discharged substances presumably stay with the water after discharge, either on slowly settling particles or in solution. They will travel with the different plank- tonic organisms in the water. There is little information on their interaction with these plankton. We can infer from the ability of DDT to accumulate in pelicans that there may be interactions. DDT was discharged for several years through a Los Angeles County Sanitation District outfall off Palos Verdes. Pelicans throughout the Southern California Bight accumulated it, and as a consequence were unable to maintain their population levels. Eggshell thinning and subsequent reproductive failures implicated the DDT from the outfall. This accumulation by pelicans implies that the sewage effluent was interacting with planktonic organisms because (1) pelicans must have derived their ODT from the surface fishes (such as anchovy and sardines) that they eat, and (2) surface fish accumulated DDT from the plankton in their diets or directly from the water. Thus, discharged waste can be in contact with plankton long enough to have an impact on these higher-trophic-level organisms. The waste/seawater mixture created by a discharge does not simply drift into oblivion. In coastal areas such as the Southern California Bight, circulation and exchange with the open ocean can be inhibited by subsurface topography. Large-scale circulation rates as well as local advection determine contaminant concentrations over large areas. We expect slower water exchange in deeper waters because topographical constraints also increase with depth. Trace-metal concentration measurements in more than 500 m of water off the southern California coast by Barcelona et al. (1982) suggest that regional near-surface discharge has increased copper concentrations two to five times. This was in areas more than 15 km from the nearest major sewage outfall. Thus, far-field processes are important aspects of waste disposal. The spatial scale over which this occurs implies that releases
70 2.5.1 Assessment of Capabilities Predictive capabilities exist now to provide first approximations in many cases of the concentrations and fluxes of substances critical to the examination of impacts of ocean disposal systems. Specific combinations of waste, site, and disposal system characteristics result in predictions with greater certainty than do other combinations. For example, predictions of transport and dispersion of wastes in the immediate vicinity of most discharge devices (near-field region) are generally well in hand, while predictions involving larger time and space scales are often less certain. Dissolved oxygen concentrations can be predicted with confidence in some cases, but knowledge of the processes governing the fate of synthetic organics is limited. 2.5.2 Information Needs Resulting from Prediction In addition to the information needed for developing predictions of concentrations and fluxes, including model calibration, information needs are created by the pre- diction process itself. The primary purpose of a prediction is to link or integrate processes affecting concentrations in ways not obvious from independent consideration of each process. Examination of the responses of the linked system to variations in inputs (site, waste, and discharge system), as well as to the representations of the processes themselves, create new information requirements. Response and sensitivity studies provide insight into those data that appear most critical in the determination of concentrations and fluxes. Early evaluation of predictions allows the collection of additional data to reduce uncertainty. Early prediction exercises are important to the design of programs for monitoring and assessing postconstruction performance. REFERENCES Barcelona, M. J., L. C. Cummings, S. H. Lieberman, H. S. Fastenau, and W. J. North. 1982. Marine farming in the coastal zone: chemical and hydrographic considerations. Calif. Cdop. Fish. Invest. Rep. 23:180-187.
