Baixe Environmental Modeling-Jerald L Schnoor-Chapter 01 e outras Notas de estudo em PDF para Engenharia Ambiental, somente na Docsity! | Environmental - Modeling - ENVIRONMENTA A WILEY-INTERSCIENCE ENVIRONMENTAL SCIENCE AND TECHNOLOGY A Wiley-Interscience Series of Texts and Monographs Edited by JERALD L. SCHNOOR, University of lowa ALEXANDER ZEHNDER, Swiss Federal Institute for Water Resources and Water Pollution Control A complete list of the titles in this series appears at the end of this volume xiv Contents 43 44 4.5 4.6 47 48 4.9 a 5.1 5.2 5.3 54 5.5 5.6 5.7 5.8 5.9 5.10 Numerical Solution Technique . Surface Complexation and Adsorption vei Precipitation and Dissolution in Equilibrium Mo els Redox Reactions in Equilibrium Models Computer Models References Problems . Eutrophication of Lakes Introduction Stoichiometry Phosphorus as a Limiting Nutrient Mass Balance on Total Phosphorus in Lakes Nutrient Loading Criteria Relationship to Standing Crop Land Use and Bioavailability Dynamic Ecosystem Models for Eutrophication Assessments References Problems 6. Conventional Pollutants in Rivers 6.1 6.2 6.3 64 6.5 6.6 6.7 6.8 6.9 Introduction Mass Balance Equation: Plug-Flow System Streeter-Phelps Equation Modifications to Streeter-Phelps Equation Waste Load Allocations Uncertainty Analysis Dissolved Oxygen in Large Rivers and Estuaries References Problems 7. Toxic Organic Chemicals Tl 72 Tl 74 7.5 7.6 Nomenclature Organics Reactions Organic Chemicals in Lakes Organic Chemicals in Rivers and Estuaries References Problems 8. Modeling Trace Metals 8.1 82 83 Introduction Mass Balance and Waste Load Allocation for Rivers Complex Formation and Solubility 145 149 165 166 178 180 182 185 185 187 190 193 195 199 201 203 214 215 221 221 225 232 243 250 259 270 295 295 305 305 307 347 365 376 378 381 381 387 397 8.4 8.5 8.6 8.7 8.8 8.9 810 Contents Surface Complexation/Adsorption Steady-State Model for Metals in Lakes Redox Reactions and Trace Metals Metals Migration in Soils Closure References Problems 9. Groundwater Contamination 10. 11. 9.1 92 9,3 94 9.5 9.6 97 9.8 9.9 9.10 9.11 9.12 9:13 9.14 Introduction Darcy's Law Flow Equations Contaminant Solute Transport Equation Sorption, Retardation, and Reactions Biotransformations Redox Reactions Nonaqueous Phase Liquids Biofilms and Bioavailability Unsaturated Zone Remediation Numerical Methods References Problems Atmospheric Deposition and Biogeochemistry 10.1 10,2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 Genesis of Acid Deposition Acidity and Alkalinity; Neutralizing Capacities Wet and Dry Deposition Processes that Modify the ANC of Soils and Waters Biogeochemical Models Ecological Effects Critical Loads Case Studies Metals Deposition References Global Change and Global Cycles 11 11.2 11.3 11,4 11.5 11.6 Introduction Climate Change and General Circulation Models Global Carbon Box Model Nitrogen Cycle Global Sulfur Cycle Trace Gases Xv 414 423 431 443 449 449 451 455 455 457 466 470 473 484 492 501 509 517 521 523 525 527 531 531 542 547 553 572 579 582 589 595 600 605 605 612 619 637 642 649 xvi Contents 11,7 References 655 11.8 Problems 657 Appendix A. Dissolved Oxygen as à Function of Salinity 660 and Temperature Appendix B. Dimensions, Units, Conversions 661 663 Appendix C. Complementary Error Function Appendix D. Runge Kutta Fourth Order Accurate Numerical Model 664 for PCBs in the Great Lakes gram for Aluminum 667 | Appendix E. Chemical Equilibrium FORTRAN Pro: Raphson Speciation in Natural Waters Using à Newton- Interative Technique Implicit Finite Difference Numerical Technique for sh) Advective-Dispersion Equation in a Vertically Stratified Lake or Reservoir Appendix F. Index 676 1.2 Mass Balances 3 1.2 MASS BALANCES Water quality may be defined as “something inherent or distinctive about water” These distinctive characteristics can be chemical, physical, or biological parame- ters. Most water quality parameters are measured in mass quantities or concentra- tion units (mg, mg L”!, moles liter!). Thus we frequently use a mass balance to de- termine the fate of these parameters in natural waters and to assess degree of pollution expected under various conditions. The fate of chemicals in the aquatic environment is determined by two factors: their reactivity and the rate of their physical transport through the environment. All mathematical models of the fate of chemicals are simply useful accounting proce- dures for the calculation of these processes as they become quite detailed. To the ex- tent that we can accurately predict the chemical, biological, and physical reactions and transport of chemical substances, we can “model” their fate and persistence and the inevitable exposure to aquatic organisms. Figure 1.1 is a schematic of the mass balance modeling approach to the solution of mass transport problems with chemical reaction. Key elements in a mass balance are defined below: (1) A clearly defined control volume. (11) A knowledge of inputs and outputs that cross the boundary of the control volume. (iii) A knowledge of the transport characteristics within the control volume and across its boundaries. (iv) A knowledge of the reaction kinetics within the control volume. CONTROL VOLUME (Water body) Physical, Chemical, Biological Reactions Transport out MASS OUTFLOW Figure 1,1 Generalized approach for mass balance models utilizing the control-volume concept and transport across boundaries. 4 Introduction A control volume can be as small as an infinitesimal thin slice of water j swiftly flowing stream or as large as the entire body of oceans on the planet Bart The important point is that the boundaries are clearly defined with Tespect to their location (element i) so that the volume is known and mass fluxes across the bound - aries can be determined (element ii). Within the control volume, the transport char. acteristics (degree of mixing) must be known either by measurement or an estimate based on the hydrodynamics of the system. Likewise, the transport in adjacent or surrounding control volumes may contribute mass to the control volume (much as smoke can travel from another room to your room within a house), so transport O the boundaries of the control volume must be known or estimated (element NI). A knowledge of the chemical, biological, and physical reactions that the sub. stance can undergo within the control volume (element iv) is needed. If there were no degradation reactions taking place in aquatic ecosystems, every pollutant that was ever released to the environment would still be here to haunt us. Fortunately, there are natural purification processes that serve to assimilate some wastes and to ameliorate aquatic impacts. We must understand theso reactions from a quantitative viewpoint in order to assess the potential damage to thc environment from pollutant discharges and to allocate allowable limits for these discharges. A mass balance is simply an accounting of mass inputs, outputs, reactions, and accumulation as described by the following equation: Accumulation within Mass Mass . =. - + Reactions (1) the control volume inputs outflows Transport It is the subject of Chapter 2 to describe the mathematical formulation for the “Transport” terms in equation (1), and it is the subject of Chapters 3, 4, and 7 to de- scribe environmental chemical models for the “Reactions” term in equation (1). Mass balances are based on first principles (continuity) and are the foundation for this entire book. Chapters 5-11 are applications and examples of the power and util- ity of this approach. If a chemical is being formed within the control volume (such as the combina- tion of two reactants to form a product, A + B — P), then the algebraic signin fon of the “Reactions” term is positive when writing a mass balance for the produet. | the chemical is being destroyed or degraded within the control volume, then pd gebraic sign of the “Reactions” term is negative. If the chemical is conservatiY (i.e., nonreactive or inert), the “Reactions” term is zero. (2) Accumulation = Inputs — Outflows + Reactions A list of reactive and nonreactive chemicals are provided in Table 1.1, which are considered in later chapters. est to If the system is at steady state (i.e., no change in concentration with resP many of 1.2 Mass Balances 5 Table 1.1 Classification of Substances Relative to Their Reactions in Water (Aqueous Phase) Reaction Formation (+) Reaction Degradation (-) Conservative Substances Products in chemical Reactants in chemical Rhodamine WTº dye reactions reactions Chloride, bromide Algal growth Biochemical oxygen Total dissolved solids (TDS) Bacterial growth demand (BOD) Nonbiodegradable organics Gas absorption Radioisotope decay Total metal Chemical desorption Particle sedimentation Stable isotopes (N, C) Bacteria die-away Organics degradations Gas stripping Chemical adsorption “time, dC/dt = 0), then there is no accumulation in the system and outflows are sim- ply equal to inputs plus or minus reactions. Outflows = Inputs + Reactions The importance of an accurate mass balance for water cannot be overempha- sized. Without a good water balance it is impossible to obtain an accurate mass bal- ance for the aquatic chemical of interest. Water can be viewed as a conservative sub- stance with numerous inputs and outflows from the water body. The accumulation of mass of water is termed the “change in storage” If the system is nearly isother- mal, then the mass of storage is accounted for by the volume of inflows and out- flows. “AStorage = XInflows — * Outflows + Dircct precipitation — Evaporation (4) Inflows may include the volumetric inputs of tributaries and overland flow; out- flows are all discharges from the water body; direct precipitation is the water that falls directly on the surface, while evaporation is the volume of water that leaves the surface of the water body to the atmosphere. AStorage can be measured in lakes or rivers by a change in elevation or stage. Inflows and outflows should be gaged or measured frequently during the period of investigation. Precipitation gages and evaporation pans can be utilized with sufficient accuracy to measure direct precipi- tation and evaporation. If the lake or stream basin is not sufficiently “tight” with re- spect to inputs or outflows to groundwater (GW), the piezometric surface of the groundwater adjacent to the water body must also be measured in order to deter- mine the magnitude of the interaction. AStorage = XInflows + GW Inputs — XOutflows — GW Outseepage + Direct precipitation — Evaporation (5) 8 Introduction 0 px 10º 10 9.87x 108 30 9.70 x 108 50 8.49 x 108 100 4.82 x 108 143 0 Example 1.2 Algebraic Mass Balance on Toxic Chemical in a Lake c chemical in a lake under the fol- Calculate the steady-state concentration of à toxi 0) and constant volume (O; = lowing conditions. Assume steady state (ac/dt = Qou) and a degradation rate of 50 kg d!. Given Cy = 100 pg 1 On = Qou = 10 mº s! “Ran = 50kg d! ake as a control volume [Equa- Solution: Write the mass balance equation for the 1 tion (1)]. Accumulation = Inputs — Outflows = Rxns Accumulation = O at steady state Outflows = Inputs — Rxn (degradation) Oou * Com = Qin X Cin— Rxn (0 mês!) x Cow = (10 mês!) (100 ug L-!)-50 kg d” * 10mê 100pg 1000L 86,400s 8 Oin X Cin> —— 5 L mé d 10º pg — Massperday 36.4 kgd! Dou 10m? si Convert units into ng LD Con=421 pg Lo! Simple mass balance models yield an expected concentration of chemical species. If the model is steady state, the answer is constant with time (e.g. Example 1.2). If the model is time variable, then the predicted state variable changes over 1.3 Model Calibration and Verification 9 time, as in Example 1.1. Spatially, mathematical models of aquatic chemicals may be one-, two-, or three-dimensional. Models can be homogeneous or heterogeneous in terms of the physical setting of the prototype (the natural system being modeled). For example, a groundwater aquifer may consist of sand deposits with a clay lense of different porosity and permeability. Most of the models in this text are deterministic (i.e., they have one expected outcome for a given initial condition and model parameters). However, we will dis- cuss uncertainty analysis using a probabilistic (stochastic) model that will allow prediction of not only the expected outcome (mean or best estimate) but also the variance of that estimate. In the future, mathematical models should provide deci- Sons with a best estimate and a standard deviation (how certain one is of the results). 1.3 MODEL CALIBRATION AND VERIFICATION To perform mathematical modeling of aquatic chemicals, four ingredients are nec- essary: (1) field data on chemical concentrations and mass discharge inputs, (2) a mathematical model formulation, (3) rate constants and equilibrium coefficients for the mathematical model, and (4) some performance criteria with which to judge the model. . Without field data, model calibration and verification are impossible. Depending on the ultimate use of the model, the amount of field reconnaissance varies. If the model is to be used for regulatory purposes, there should be enough field data to be confident of model results. Usually this requires two sets of field measurements, one for model calibration and one for verification under somewhat different circum- stances (a different year of field measurements or an alternate site). Model calibration involves à comparison between simulation results and field measurements. Model coefficients and rate constants should be chosen initially from literature or laboratory studies. Flow discharge rates are also needed as input to drive the model. After you run the model, a statistical comparison is made be- tween model results for the state variables (chemical concentrations) and field mea- surements. If errors are within an acceptable tolerance level, the model is consid- ered calibrated. If errors are not acceptable, rate constants and coefficients must be systematically varied (tuning the model) to obtain an acceptable simulation. The pa- rameters should not be “tuned” outside the range of experimentally determined val- ves reported in the literature. Thus the model is calibrated. A few definitions may be helpful relating to model calibration and verification. Mathematical model—a quantitative formulation of chemical, physical, and bio- logical processes that simulates the system. State variable—the dependent variable that is being modeled (in this context, usually a chemical concentration). Model parameters—coefficients in the model that are used to formulate the mass 10 Introduction balance equation (e.g., rate constants, equilibrium constants, Stoichiometrie ratios). Model inputs—forcing functions or const flowrate, input chemical concentrations, temf Calibration—a statistically acceptable comparison between model results and field measurements; adjustment or “tuning of model parameters IS allowed within the range of experimentally determined values reported in the litera. ture. Verification—a statistically acceptable comparison between model results and à second (independent) set of field data for another year or at an alternate site; model parameters are fixed and no further adjustment is allowed after the ca]. ibration step. Simulation—use of the model with any input data set (even hypothetical input) and not requiring calibration or verification with field data. Validation—scientific acceptance that (1) the model includes all major and salient processes, (2) the processes are formulated correctly, and (3) the mod- el suitably describes observed phenomena for the use intended. Robustness—utility of the model established after repeated applications under different circumstances and at different sites. ants required to run the mode] . (e. temperature, sunlight). 8 Post audit—a comparison of model predictions to future field measurements at that time. Sensitivity analysis —determination of the effect of a small change in model pa- rameters on the results (state variable), either by numerical simulation or mathematical techniques. Uncertainty analysis—determination of the uncertainty (standard deviation) of the state variable expected value (mean) due to uncertainty in model parame- ters, inputs, or initial state via stochastic modeling techniques. Statistical criteria for acceptance of model calibration and verification should be established a priori, before the simulations are begun. How “good” the model re- sults are depends on desired use of the model or predictions. Likewise, criteria for acceptance of a calibration or verification depend on the intended usc of the model. For example, a criterion for accept might be: be within + 0.5 mg L”! in at least 9 o oe “ceptance of a dissolved oxygen model calibration The prediction of dissolved oxygen concentration in the stream should 0% of the observations” There are several other types of statistical criteria that can be established. . Statistical “goodness of fit” criteria Using chi-square or Kolmogorov- Smirnov tests (tests of the sampling distribution of the variance). * Paired t-tests of model results and fi a . eld observ: e (a test of the means). ations at the same time ( º Linear regression of paired data fo icti d ob: à r model pri i rvations ita fame tio, predictions and fiel se! 1.3 Model Calibration and Verification 13 3 (observed value, — expected value; Ms x 1 expected value í where the observed values are the D.O. field data, and the expected values are the D.O. model results. In order to accept the model results as a good fit, PO sx)=1-a where a is the confidence level and = xg is the chi-square distribution value for n — 1 degrees of freedom. The criterion for the D.O. modeling effort is Pb? = 4.17)=0.10 where x2 = 4.17 for n = 10 and « = 0.9. The value for xg = 4.17 was determined from a statistical table for the chi-square distribution with 9 degrees of freedom (n— 1) and P=0.10, The table below shows that 0.1254 < 4.17 Therefore the model passes the goodness of fit test at a 0.10 significance level. Distance x d; (obs, — expect,) 2 0 0 0 0 5 0.0143 03 0.09 10 0.0019 01 0.01 20 0.0071 —0.18 0.0324 30 0.0003 —0.04 0.0016 40 0.0706 -0,6 0.36 50 0.0164 -03 0.09 60 0 0 0 80 0.0134 03 0.09 100 0.0014 01 0.01 0.1254 -032 0.684 b. The paired t-test is used to test the difference between pairs of data at a speci- fied confidence limit. The test statistic is - dVn 5 t 14 Introduction where + pá q= é n d; = difference between values in data pair; Sd nº q Sy= Sd E) n-1 n-1 The acceptance criterion for the i-test is Pl =i)=p forn— 1 degrees of freedom. The criterion for the D.O. model is P(t < 1.833)= 0.10 The value 1.833 was determined from a table of t-values with 9 degrees of freedom and P=0.10. The table above shows Zd=-0.32 and Sdf=0.684 The test statistic can be calculated: d= -0.32 = 0.032 10 0.684 10 Sy= “o To (0.032)? = 0.2736 9 0.032 410 t= = 02736 — 03699 The model results are found to be indistinguishable from the field data at a sig- nificance level of 0.10 from the paired r-test because 0.3699 = 1.833 There is less than a 10% probability that these two populations of data (model and field observations) could have been selected randomly from different distribu- tions. The model meets the statistical criteria selected for means c. Perfect model predictions would yield , »=10x+0 1.3 Model Calibration and Verification 15 Table 1.2 Table of Significant Reactions for Selected Priority Pollutant Organic Chemicals in Natural Waters? Sorption/ Biotrans- Chemical Chemical Phototrans- Volatili- Bioconcen- formations -Hydrolysis Oxidation formations zation tration Pesticides Acrolein x x DDT--chlorinated x x x hydrocarbon Parathion-organo- x x x P ester TCDD—tetra- x x chlorodibenzo- p-dioxin Polychlorinated biphenyls (PCBs) Aroclor 1248 x x x Halogenated aliphatic hydrocarbons Chloroform x x x Halogenated ethers 2-Chloroethyl x x x x vinyl ether Monocyclic aromatics 2,4-Dimethylphenol x Pentachlorophenol x x Phthalate esters Bis(2-ethyl- x x x x hexylDphthalate Polycyclic aromatic hydrocarbons Anthracene x x x x x Benzo[alpyrene x x x Nitrosamines and miscellaneous Benzidine x x x x Dimethyl x x nitrosamine 18 Introduction continue to cause the eutrophication of surface waters, oxygen eia Of sedi. ments, habitat alteration, and ecological changes in the nd and function of the ecosystem that are often difficult to detect, quantify, an oa 4 E The ability of a trace element to pose an environmental hazar epends Not on on its enrichment in the atmosphere or hydrosphere but also on its chemical specia. tion (form of occurrence) and the details of its biochemical cycling. Bioavailabiliy and toxicity depend strongly on the chemical species. For algae and lower organ. isms, the free metal aquo ions often determine the physiological and ecological re. sponse.?4-26 o. Particles are scavengers for reactive chemical species in transport from land ty rivers and from continents to the ocean floor. Hydrous oxide surfaces, as well as or. ganically coated surfaces, contain functional surface groups that act as coordinating sites for reactive elements. Metals and adsorption to hydrous oxides are discussed in Chapters 4 and 8. At present the open ocean and many lakes are more affected by pollution impacts through tropospheric transport than through riverine transport. Elements are termed atmophile when their mass transport to the sea is greater from the atmosphere than from transport by streams. This is the case for Cd, Hg, As, Se, Cu, Zn, Sn, and Pb, Atmophile elements are either volatile, or their oxides or other compounds have low boiling points. The elements Hg, As, Se, Sn, and perhaps Pb can also become methylated and are released in gaseous form into the atmosphere. The elements Al, Ti, Mn, Co, Cr, V, and Ni are termed lithophiles because their mass transport to the ocean occurs primarily by streams. Soft Lewis acids, metals such as Cu*, Ag, Cd?*, Zn?*, Hg?*, and Pb?*, and the transition metal cations (Mn?*, Fe?*, Ni?*, Cu?*) are of environmental concern, both from a point of view of anthropogenic emissions as well as hazard to ecosystems and human health (chemical reactivity with biomolecules).?” Of special concem are organometallic compounds such as organotin compounds.28.29 Considering the schematic reaction, Igneous rock + Volatile substances = Air + Seawater + Sediments reacted in a gigantic acid-base reaction with the bases of the rocks (silicates, car- bonates, oxides). Similarly, he calculated ftom a model system the quantities of re- duction and oxidation components that have Participated in a redox titration. On the global average, the environment with Tegard to a proton and electron balance is in 3 pi pe which reflects the Present-day atmosphere (20.9% O», 0.03% 2 12:L% No), an ocean pH of -8, and à . Naa ar- tial pressure of O, equal to 0.21 atm, Tedox potential corresponding to à P ciiliatioa (Cia is tir markedly at least locally and regionally by OU » n local environ - up- set and significant variations in ments KH? and e- balances may become UP PH and pe occur. In the present competition be- 1.4 Enviromental Modeling and Ecotoxicology 19 tween anthropogenic, geochemical, and biochemical processes, redox conditions in the atmosphere are disturbed by enhanced rates of artificial weathering of fossil fuel?! The combustion of these fuels leads to a disturbance in the electron (reduc- tion-oxidation) balance, The reactions of the oxidation of C, S, and N exceed reduc- tion reactions in these elemental cycles. A net production of hydrogen ions (acids) in atmospheric precipitation is a necessary consequence.*? Furthermore, many more potential atmospheric pollutants (photooxidants, polyeyclic aromatic hydrocarbons, smog particles, etc.) are formed under the influence of photochemically induced in- teractions with OH radicals, H,0,, ozone, and hydrocarbons with fossil fuel com- bustion products. The disturbance is transferred to the terrestrial, aquatic (mostly freshwater), estuarine, or coastal marine environment. Atmospheric acid deposition creates an additional input of hydrogen ions and sulfate and nitrate (sulfuric and ni- tric acid) to terrestrial and aquatic ecosystems. The atmosphere has become an important conveyor belt for many potential aquatic pollutants. Many persistent pollutants are present in a vapor phase during transport from land to fresh water and from continent to ocean. Even substances with vapor pressures as low as 107!º atm are released into the atmosphere. These substances include many pesticides, such as DDT, more volatile metals (Hg), metal- loids (As, Se), or their compounds. At present the open ocean is probably more af- fected by metal pollution inputs through tropospheric transport than through river transport (Pb). The hydrogeochemical cycles couple land, water, and air and make these reservoirs interdependent (Figure 1.6). In Figure 1.6 the sizes of the various reservoirs, measured in number of mole- cules or atoms, are compared. The mean residence time of the molecules in these reservoits is also indicated. The smaller the relative reservoir size and residence time, the more sensitive the reservoir toward perturbation. Obviously, the atmos- phere, living biomass (mostly forests), and ground and surface fresh waters are most sensitive to perturbation. The anthropogenic exploitation of the larger sedi- mentary organic carbon reservoir (fossil fuels and by-products of their combustion such as oxides and heavy metals and the synthetic chemicals derived from organic carbon) can above all affect the small reservoirs. Over the past years we have started to recognize that biosphere processes play an important role in coupling the cycles of essential elements and in regulating the chemistry and physics of our environ- ment, The living biomass (Figure 1.6) is a relatively small reservoir and thus subject to human interference; each species forming the biosphere requires specific envi- ronmental conditions for sustenance and survival Transport of pollutants from air to water and ftom land to water have become in- creasingly important pathways for the occurrence of water pollution (Figure 1.7). Degradation of groundwater from soil pollution is a major environmental problem (e.g., infiltration of pesticides from agricultural applications or leachate from haz- ardous waste landfills). Also, impacts of acid deposition on surface waters and oxi- dants on forests and soils illustrate the importance of transport through the air- water interface. We need to know about the aquatic chemistry of these pollutants to estimate their speciation and fate in the environment, and we need to know how to 8 3 E 8 AS = 8 Em 4é Sã 5 it & E E Z 1097 4 H,0 Oceans 1=4x10 e 1046 SiO2 in sediments 1=5x 108 = 108 C Organic carbon in sediments t= 10 FT Atmosphere No + 02 + C0z No Atmosphere t=5x107 q O» Atmosphere T=7x105 H5 O Fresh surface waters t=l To Organic C (biomass) t=5 Living 8 Da biomass Forests, plants, co, Atmosphere 1=6 pm, ” o 16 animals Ra Organic N (biomass) t=10 3 10 10 38 CH T=9 10 101! ” 10 ; 3 Organic C Anthroposphere ——— ho ! 10º NO ;+ HNO3 Atmosphere 7=0.1 NHs +NH$ Atmosphere 7=001 HS + 502 + H9S04 Atmosphere 7=0.02 MM Figure 1.6 Comparison of global reservoirs. The Feservoi ing biomass are significantly smaller than the pipas groundwater reservoir may be twice that of fresh wat A (7 = respective residence time [years] of molecule [atom s Of atmosphere, surface fresh waters, s of sediment and marine waters. However, groundwater is much less s].)35 1.4 Enviromental Modeling and Ecotoxicology 23 served in laboratory experiments to organisms in nature, from one organism to an- other or to humans. The natural distribution of organisms depends primarily on their ability to com- pete under given conditions and not merely on their ability to survive the physical and chemical environment. A population will be eliminated when its competitive power is reduced to such an extent that it can be replaced by another species. The competitive abilities of an organism are based on its reproductive rate (which is re- lated to food and physiological potential), and the mortality rate from all causes, in- cluding predation and imposed toxicity. There are many ways in which an organism can die, but there is only a very narrow range of ways in which it can survive and leave offspring. Thus, in an ecosystem, a population may be eliminated by the pres- ence of pollutants even at apparently trivial toxicity levels if its competitive ability is marginal, or if it is the most sensitive of the competitors. Often, contaminants at very low concentrations cause changes in the structure of the population by interfering through chemotaxis with interorganismic communica- tion. For example, the survival of a fish population may be rendered impossible by a pollutant (even if it exhibits neither acute nor chronic toxicity to the particular species of fish) if it impairs the food source (zooplankton) or disturbs chemotactical stimuli or mimics wrong signals (and thus, for example, interferes with food find- ing). As a conseguence of the many microhabitats (niches) that are typically present in a “healthy” water, many species can survive. Because of interspecies competition, most species are present in a low population density. Pollution destroys microhabi- tats, diminishes the chance of survival for some of the species, and thus in turn re- duces the competition; the more tolerant species become more numerous. This shift in the frequency distribution of the species toward a lower diversity of the ecosys- tem is a general consequence of the chemical impact on waters by substances not indigenous to nature. An understanding of the interaction of chemical compounds in the natural sys- tem hinges on the recognition of the compositional complexity of the environment. This requires an adequate analytical methodology, especially the ability to predict individual components (chemical species) selectively, to measure them accurately and with sensitivity, and to forecast their fate with environmental models. Table 1.3 lists water quality criteria toxicity thresholds, carcinogenicity, and maximum conta- minant levels (M.C.L.) for many toxic chemicals discharged to natural waters. It was updated by EPA in 1994. Water quality criteria are the best scientific infor- mation from toxicological studies of the maximum concentration allowable that will not cause an observable biological effect. Water quality standards are enforceable by law; they include the water quality criteria, a designated use for the water body, and a nondegradation clause. As ecotoxicology becomes more sophisticated as a science, the list of chemicals will grow and species specific criteria will be promul- gated under various environmental conditions. » Table 1.3 Water Quality Criteria and Acute and Chronic Threshold Levels for Various Toxicants!? WQ Criteria, Concentrations in gg L”! Human Health Criteria, units per liter Number Fresh Fresh Marine Marine Water Drinking of States Priority Carci Acute Chronic Acute Chronic and Organisms Water Date/ with Aquatic Pollutant nogen Criteria Criteria Criteria Criteria Organisms Only MCL Reference” Life Standard Acenapthene Y N 1,700” 520º 9704 no 1980/FR 1 Acrolein Y N 684 at. 55* 320. neo 780.ng 1980/FR 1 Acrylonitrile Y Yo 7,5508 2,600 0058ug” 0.65ug 1980/FR Aldrin Y Y 30 13 0.074ng” 0.079ngº 1980/FR 16 Alkalinity N N 20,000. 1976/RB Ammonia N N 1985/FR 24 Antimony Y N 88» 304 1,500 500 — 146.pg 45,000.pg 1980/FR 1 Arsenic Y Y 22ng 17.5ng” 005mg 1980/FR 2a Arsenic (pent) Y Y 850.» 23194 1985/FR un Arsenio (tri) Y Y 360. 190. 69. 36. 1985/FR a Asbestos Y Y 30kf Lic 7mfL 1980FR Bacteria N N <1/100ml 1986/FR 56 Barium N N Lmg 20mg 197%6/RB 8 Benzene Y Y 5,300. 5,100” 700. 066 ng 40.pngo Spg! I980FR 1 Benzidine Y Y 2,500,2 0.12 ng” 0.53 ng” 1980/FR 6 Beryllium Y Y 130.4 53º 3.7 ng” 64. ngº 4pg —1980FR 8 BHC Y N 100.+ 034" 1980/FR Cadmium Y N 3.94 14 43. 93 10. ng 0.005 mg 1985/FR 2 Carbon tetrachloride Y Y 35,200? 50,000.» 04 pe” 694ug” Sug” 1980FR 1 Chlordane Y Y 24 0.0043 0.09 0004 046ngº 048ng” 2pg” I9B0/FR 12 Chiorinated benzenes Y Y 2504 E 160 129. 488.pg” 75-100 pg! 1980/FR 1 Chiorinated naphthalenes x E 16002 n 1 15 / LSseR E Chtorine st Chloroalkyl ethers Chloroethyl ether (bis-2) Chloroform Chlorophenol, 2- Chlorophenol, 4- Chlorophenoxy herbicides (2, Chlorophenoxy herbicides (2,.4-D) Chioropyrifos Chloro-4 methyI-3 phenot Chromium (hex) Chromium (tri) Color Copper Cyanide DDT DDT metabolite (DDE) DDT metabolite (LDF) Demeton Dibutylphthalate Dichlorobenzenes Dichlorobenzidine Dichloroethane 1,2 Dichloroethylenes Dichloropheno! 2,4 Dichloropropane Dichloropropene Dieldrin TP) ZZMmM MA z KHZ dd dA A Md rd 7 Zzz4<47 z tZEZZ4ANZZZAEA ZA 238,000.* 28,900 1,240º 4380.» 29,700º 0083 0041 001] 304 16. 1,100. 17007 2107 10,300 181 nf 2.9 22 52 L 1 0001 013 1,050.» 144 0.6º 36 01 1,120º 7634 19704 118,000! 20,000º 113,04 11,600.º 2240008 2,020º — 365+ 23,000º 5,700º 10,304 6060.” 2442 7904 25 0.0019 0.71 0.0056 so. 0.001 01 3,040+ 019 0.03 pg 0.19 ngr 10. pg 100. ng 50. ng 170.mg 200. ng 0.024 ngº 35.mg 400. pg 0.01 ug 0.94 pg” 0.033 pgs 309mg 87. ug 0.071 ng 1980/FR 1980/FR 1980/FR 1980/FR 1980/FR 1980/FR 136 pg” 15.7ug 100 pg! 50 pe” 70 ng” 1976RB 1986/FR 1980/FR 1985/FR 1985/FR 1976/RB 1985/FR 1985/FR 1980/FR 1980/FR 1980/FR 1976/RB 154. mg 1980/FR 2.6mg 0.075-0.6 mg?1980/FR 0.020 pg” 1980/FR 243. ug” Sug! 1980FR 185ug” 7-100 pg” 1980/FR 1980/FR 1980/FR 1980/FR 1980/FR 0.10 mg 3433. mg 0.10mg 13mg 02mg 0.024 ng” Sung! 14.1 mg 0.76 ng 24 24 20 23 16 1 1 1 1 1 1 1 16 (continued) st Table 1.3 (Contimued) WQ Criteria, Concentrations in pg L-! Human Health Criteria, units per liter Number Fresh Fresh Marine Marine Water Drinking of States Priority Carci Acute Chronic Acute Chronic and Organisms Water Date” with Aquatic Pollutant nogen Criteria Criteria Criteria Criteria Organisis Only MCL Reference” Life Standard Oil and grease N N 1976/RB 56 Oxygen dissolved N N 5,000 4,000 1986/FR 56 Parathion N N 0065 0.013 1986/FR 8 PCBs Y Y 20 0.014 10. 003 007ng 007ng” 0.5pg” 1980/FR 16 Pentachlorinated ethane | N No 72408 1,100" 390% 2814 1980/FR 1 Pentachlorobenzene N N 74. 48 85. pg 1980/FR Pentachlorophenol Y N 208 38 13. 798 — 10lmg 10 pg” 1986/FR 2 pH N N 659 6585 5-9 1976/RB 56 Phenol Y N 10,200” 2,560º 5,800” 3.5me 1980/FR 23 Phosphorus elemental N N 0.1 1976/RB Polynuclear aromatic Y Y 300» 28ng 3LI ng 1980/FR 1 bydrocasbons Selenium Y N 20. 50 300. mn. 10. pg 50. ug 1980/FR 15 Silver Y N sv 012 23 092ug 50. pg 1980/FR 14 Solids dissolved and N N 250. mg 1976/RB 56 salâmity Solids suspended and N N 1976/RB 44 turbidity 6 Sulfide-hydrogen sulfide N N 2 2 1976RB Temperature N N | SPECIES-DEPENDENT CRITERIA 1976/RB 56 Tetrachlorobenzenc 1,2,4,5 N N 38. ug 48. ng 1980/FR Tetrachloroethane 1,1,2,2 Y Y 2,400 9,0204 0.17 pg” 10.7 pao 1980/FR 1 Tetrachlorocihanes Y Nº 93204 1980/FR t Tetrachloroethylene Y Yo 5280” 8408 102008 450 OBug 885pg Spg! I9S0FR 1 Tetrachlorophenol 2,3,5,6 N N 440. 1980/FR Thallium Y N 1400” 40! 21304 13.pg 48.pg 2pg 1980FR 2 Toluene Y No 175004 6300» 5000” 143mg 424mg 1Omg” 1980/FR 1 Toxaphene Y Y 0.73 00002 0.21 0.0002 0.7 ng 0.73 ng” Sung” I986FR 17 Trichlorinated ethanes Y Y 18,000 1980/FR Trichloroethane 1,1,1 Y N 31,200 184mg 103g — O2mg” 1980/FR 1 Trichloroethane 1,1,2 Y Y 9,400.4 O6ugo ALBng Spg I9SOFR 1 Trichloroethylene Y Yo 450008 21,900! 2,000 2748 BOTuE Sug” I980FR 1 Trichloropheno! 2,4,5 N N 100. 63. 240. 1. 2,600. pg 1980/FR Trichlorophenol 2.4.6 Y Y 9704 12pg 3.6 nge 1980/FR Vinyl chloride Y Y Zug 525pgº 2hg! I9BOFR Zine Y N 1207 O 95 86 1987/FR 19 &, grams; mg, miligrams; pg, micrograms; ng, nanograms; f, fibers; Y, Yes; N, No; MCL, “ FR, Federal Register; RB, Quality Criteria for Water, 1976 (Redbook). PImsufficient data to develop criteria, Value presented is the LOEL—Lowest observed effect level. “Human health criteria for carcinogens reported for three risk levels. 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