Accidental input of pesticides into the Rhine River Environmental impact and behavior of pollutants discharged during a chemical storehousefire Paul D. Capel U.S. Geological Survey St. Paul, MN 55101
FIGURE 1
Map of the Rhine River with its monitoring statione
Walter Giger Peter Reichert Oskar Wanner Swiss Federal Institute for M e r Resources and M e r Pollution Control (EAWAG) CH-8600Dijbendorf, Switzerland
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Rhine (km)
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The Nov. 1,1986, iire at a Sandoz Ltd. storehouse at Schweizerhalle, an industrial area near Basel, Switzerland, resulted in chemical contamination of the atmosphere, the surrounding soils, and the W e River. The chemicals discharged into the Rhine caused massive kills of benthic organisms and fish (I, 2). The 90 x 50-m storehouse, which was completely destroyed hy the fire, contained pesticides (Table l), solvents, dyes, and various raw and intermediate materials. The majority of the more than 1300 metric tons of stored chemicals (3)was destroyed in the fire, but large quantities were introduced into the atmosphere, into the W i e River through runoff of the fire-fighting water, and into the soil and groundwater at the site. Public and private reaction to the fire and subsequent chemical spill was strong. Even though this was “one of the worst chemical spills the nature of the chemicals ever” (4, and the powerful self-cleansing mechanisms of the river have made the predictions of a long-term “dead” Wine unfounded. The recovery of the Rhine from this accident is well underway, but the problems from chronic chemical contamination still remain.
Importance of the Rhine The Rhiie is one of the most important rivers in Europe, comparable only to the Danube, the Po,and the Rh6ne. It has played an important role in the development of European civilition. 892 Envimn. Sci. Technol., MI. 22,NO. 9, 1988
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Originating in the Swiss Alps, the Rhine flows through Lake Constance and westward to Basel, where it turns north, forming the French-German border (Figure 1). The majority of the navigable portion of the river flows
through the Federal Republic of Germany before it reaches the Netherlands, and finally the North Sea. Its 1320 km of waterway forms the backbone of the central European navigation system and allows Basel, which is about 800
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'Input mass range i?cludes the estimates from the Swiss, German. and French authorities or 1 4 % of the quantity 01 pesticide stored in the warehouse at the time of the fire. aMeasured Water concentrations(meas)are from the sample taken NO". 1, 1986, at 15:15 at Village-Neuf. The other water conCentrationS are calculated (calc) based on the ratio of water Concentration (py/L) to amount stored (metric tons). Eliminating the minimum and maximum vdues, the range of ratios observed is 1.5-6.5. "LC, = lethal concentration for 50% of rainbow trout, except where noted. dDaphnia. *As mercury 'As zinc. QEstuaiinefish. 'Catfis carp.
km from the North Sea, to be the sole port for Switzerland. A series of canals in France between Basel and Strasbourg permits ship traffic in this region. The Rhine River is an extraordinarily important source for drinking water in the Federal Republic of Germany, the Netherlands, France, and Switzerland. Approximately 12 million people use and drink water that has been taken from the Rhine. The raw water is purified by a series of treatment steps, typicaUy involving bank filtration, ozonation, granular activated-carbon filtration, and final disinfection. As with most rivers that drain industrial and agricultural areas, the Rhine suffers considerably from chemical pollution. The large chemical and mining industries located withii the basin contribute significantly to this contamination. The Rhine has had problems for decades with heavy metals, dissolved salts, and organic chemicals. During the past decade, the river's condition has improved as a result of statutory and voluntary controls on industrial inputs. Concentrations of heavy metals' (As, Cd, Cr, Cu,Hg, Pb, and Zn) have
steadiiy decreased between 1975 and 1985 (5).Even though the Rhine's condition has improved considerably, the problem of chemical contamination still exists. Calculations based on average Bow and concentrations (5)show that in 1984, 5700 metric tons of Zn, 700 metric tons of Pb, and 9 metric tons of Hg flowed from the Rhine into the North Sea, whereas in 1985 these quantities were decreased to 2500 metric tons of Zn,270 metric tons of Pb, and 3.1 metric tons of Hg. However, these data must be cautiously interpreted because heavy-metal loads are drastically influencedby the transport behavior of particulate matter. A great effort has been made to assess the organic chemical contamination in the Rhiie by measuring surrogate (collective) parameters such as dissolved organic carbon, biological oxygen demand, and total organic halogen, as well as individualorganic pollutants.During the last several years, levels of many organic contaminants have decreased (6, 3,largely because of the construction of wastewater treatment facilities by the chemical industry. In
addition to the chronic contaminationof the river, there has been a number of isolated incidents of acute organic chemical pollution. A vivid example of this is a 1969 spill of endosulfan,which had severe ecotoxicological consequences (8).
Summary nf the accident The Sandoz storehouse contained at least 90 different chemicals, including 20 pesticides (Table I), which caused the greatest concern for the environment after the accident. Many of the pesticides were thiophosphoric acid ester insecticides; disulfoton and thiometon were the most abundant (Table 1; see Figure 2 for chemical structures). The fire, which probably started in a lot of Prussian blue dye that had been packaged the previous day, was discovered at about W 3 0 on Nov. 1, 1986, and was extinguished by 6:00 a.m. The iirt-fighting water (10,ooO-l5,ooOm3) was discharged into the Rhine, carrying contaminantsinto the river at Rhine km 159.1.Some of the chemical load entered the water column directly; some fell to the river bottom as dense, immisEnvimn. Sci.Technol..Val. 22, NO. 9, I988 993
Disulfoton, thiometon, and etrimfos were detected in the sediments after the accident (9),but their presence was not caused by sorption and subsequent sedimentation because they have only a weak tendency to sorb (disulfoton, K, 1600 mL/gOC; thiometon, K, -340 mWgOC; etrimfos, KO, -570 mL/gOC). Given these K , values and the concentration of particulate organic carbon that was present in the river, it was estimated that less than 0.5% of these compounds would be associated with particles. On the river bottom close to the discharge point, large masses of the pollutants had fallen directly to the sediments in the form of dense, immiscible globules. Such chemical globules probably had been carried down the river by current action and were deposited in the zones of low turbulence above the many dams located between Basel and Strasbourg.
-
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cible globules that consisted of mixtures of pesticides, dyes, solvents, and pyrolytic products. The exact mass of the chemicals that entered the Rhine is unknown. Estimates have been made for a few of the pesticides by the German, Swiss, and French authorities based on measured water concentrations (3, 9, 10). Probably between 1% and 3% of the mass stored entered the river water o b l e 1). The plume of chemicals, intensely colored because of its Rhodamin B dye content, hugged the south shore of the river until it reached the dam of a hydroelectric power plant 4.7 km downstream. By the time the plume had passed the dam, transverse mixing of the chemicals was nearly complete (11).
The concentrations of pesticides in the river were first measured at 1515 on Nov. 1 at Village-Neuf (km 173, Table I). These measurements can be used to estimate the concentrations of other chemicals in the same parcel of water. The ratio of the water concentration of pesticides &g/L) to the amount stored (metric tons) was calculated for seven pesticides. The highest and lowest ratios were eliminated, and the remaining five averaged -3.5, with a minimum of 1.5 and a maximum of -6.5. Assuming that all the chemicals were introduced in about the same ratios (proportional to the amount stored), the concentrations of the remaining pesticides can be estimated (Table 1) (12). From the measured and estimated chemical concentrations at VillageNeuf, a prediction can be made as to which chemicals most likely killed the fish and other aquatic life. Table 1 includes the ECso (the concentration that elicits an effective response by 50% of the population for some predetermined criteria) for Daphnia and Es0 (the lethal concentration for 50% of the population) for fish. Even though only a few Daphnia live in the flowing waters of
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994 Environ. Sci. Technol.. Vol. 22. No 9, 1988
the Rhine, the ECSDvalues provide an estimation of the chemical’s toxicity to sensitive organisms. A comparison of water concentrations to the ECso and LCso values suggests that endosulfan, formothion, and etrimfos were prohably responsible for the damage to biota. Mercury, dinitro-o-cresol (DNOC), fenitrothion, and parathion could have also contributed. Cumulative or possibly even synergistic toxic effects Esulted from the mixture of pesticides. A strong correlation was observed at Bad Honnef (km 640)between the sum of the water concentration of the major organophosphorouspesticides (disulfoton and thiometon) and the measured Daphnia toxicity (9). The minor chemicals, contained in the same parcel of water as the disulfoton and thiometon, were probably primarily responsible for these toxic effects. Following the accident the biota in the Rhine was heavily damaged for several hundred kilometers ( I , 2). Most strongly affected were the benthic organisms and the eels, which were completely eradicated for a distance of about 400 km. It is estimated by German fishery experts that 220,000 kg of eels were killed (see cover). Microorganisms, crucial to the self-cleansing activity of the river and the bank-filtration process for water purification, were not affected (3). The wave of chemicals in the river was monitored as it flowed downstream. Figure 3 presents the measured concentration vs. time profile of disulfoton as it passed four German monitoring stations (9). The other pesticides also were contained in this same parcel of water and probably had similar concentration-time profiles. The water concentration of disulfoton diminished because of dilution and elimination. The maximum concentration of the chemical wave exited the Rhine about 12 days after the accident, which is the residence time of water between Basel and the North Sea.
Environmental fate processes As illustrated in Figure 1 for disulfw ton, the total mass of many of the monitored chemicals diminished as they flowed down the Rhine (3, 9), indicating the presence of strong environmental removal processes (physical, chemical, biological, or a combination). A finite number of processes must be considered to describe or predict a chemical’s environmental fate. After a chemical substance enters the water, a number of processes will act to decrease its concentration. Besides dispersion and diffusion, chemical and microbiological transformations can occur. The substance can be transferred to the atmosphere via volatilization, to the sediments via sorption and subsequent particle deposition, or to the macrohiota via accumulation of the chemical within the organisms’ tissues. Water chemistry, sunlight intensity, air and water temperatures, biota, and residence times of the chemicals in the water all can have a significant impact on the chemical fate processes. The influence of the environmental removal processes can be illustrated by a few representative examples. A couple of the pesticides were immediately lost from the water. Among them, dichlorvos, which has a hydrolysis half-life of 0.25 days at the pH of the Rhine (pH7.4). Others, such as oxadixyl, were transported intact through the length of the river; the fastest removal process for oxadixyl is indirect photolysis (tla > 400 days). Most of the pesticides underwent partial transformation in the river via one or more of these environmental processes. The organophosphorous pesticides were significantly biodegraded. According to what is known from soil studies, the biotransformation of thiometon and
disulfoton primarily results in metabclites in which the aliphatic dialkyl sulfur atom has been oxidized (sulfoxides and sulfones). These metabolites are generally more toxic than the parent chemicals. Endosulfan probably was subject to a combination of biodegradation, sorption-sedimentation, hydrolysis, and volatilization at varying degrees. The sum of all the processes determined the fate of pesticides in the river. The hydraulic characteristics of the Rhine River contribute an important self-cleansing mechanism from chemical contamination. The residence time of water from Base1 to the North Sea is about 12 days. In the upper part of the Rhine, water currents scour the river bed, eliminating significant long-term sedimentation of fine particles in the
main channel, except in areas behind many of the dams in the upper stretches of the river. .This scouring action and the short water residence time continually purge contaminants from the river into the North Sea. If a chemical is not strongly sorbed, is nonvolatile, and is biologically and chemically persistent, it remains unchanged in the water column, undergoes dilution, and is discharged from the river at a rate equal to the water residence time. A chemical that is strongly sorbed has a longer residence time in the river; its transport is influenced by sedimentationto the river bed, resuspension, and subsequent particle transport down the river.
Fate of pesticides in the Rhine A mathematical model (11)was used to interpret the measured concentra-
tion-time series of disulfoton and thiometon and to predict the fate of the other pesticides discharged to the Rhine River. Based on discharge, water depth, and flow velocity, this one-dimensiod model calculates concentrations of chemicals in the river as a function of time and space. It incorporates advective and dispersive transport, exchange zones of stagnant water, transfer to the atmosphere and to the sediments, and transformation of the chemicals in the water body. An important feature of the model is its ability to consider every chemical, physical, or biological transformation process and its respective reaction rate. Disulfoton and thiometon have been used to validate the model because the greatest number of field measurements were made for these two compounds. For both compounds the chemical removal processes are much slower than biodegradation. A zero-order decay constant of 1.5 x 1W g m-3 sec-' for disulfoton best fits the observed Rhine data (11). This calculated disappearance rate in the Rhine is in fair agreement with the biode radation rate of 1.3 x 1W8g m3s e 3 obtained in subsequent laboratory experiments in Rhine water at 10 "C (11, 12). The measured and model concentration ro files for four Rhine stations are iius; trated for disulfoton (Figure 3). Both the loss of chemical mass and the observed tailing of the concentration-time profiles of disulfoton and thiometon are adequately described by the model. The tailing is caused both by the convective period (initial spreading) and by the exchange of water between zones of flowing and stagnant water in the river. Retainment of the chemicals in the areas of s t a p t water (11) diminished the concentration in the maximum wave. These retained chemicals, which slowly bleed out of the stagnant areas, added to the observed tailing and were eventually flushed to the North Sea. The net result was a longer residence time of the chemicals in the river. This strong confirmation of the model allows predictions to be made for the other chemicals. The concentration profiles for 11 of the organic pesticides have been calculated. Figure 4 shows the concentration profiles normalized to the respective estimated input mass, as they are modeled for the fifth monitoring site at Lobith (km 862). The elimination of the pesticides from water was described by a firstorder rate law based on environmental half-lives of biodegradation, hydrolysis, photolysis, and volatilization, which were obtained from literature, from Sandoz reprts, or by calculation. Sorption and subsequent sedimentation were determined to be unimportant for Environ. sci. Technol.. Vol. 22. No. 9,1988 995
the 11 pesticides. Figure 4 illustrates that some chemicals were completely lost within the river, whereas others were totally recalcitrant. AU of the nonmetal-based pesticides, except those that were completely removed, were predicted to have concentration-time prosles of essentially the same shape as disulfoton. The general fate of each of the 20 pesticides in the river is described in the box. Interest in the chemicals that passed out of the Rhine primarily focused on their impact on the North Sea, but this impact is still poorly understood. The weakness of these estimates lies in the accuracy of the environmental rate constants. Usually the rate of biodegradation, which can vary greatly between ecosystems, is known with the least degree of certainty. The four metal-bad pesticides must be considered separately from the organic ones. The two zinc-bad pesticides hydrolyzed very quickly. The mass of zinc resulting from the accident was unimportant compared with the typical daily load that passes Basel; the accident probably contributed less than 3% of a daily load. The two mercury compounds were of more concern, as both dissociate in water, exist as organomercuric cations (phenylmercuric and ethoxyethylmercuric cations), and strongly sorb to particles and to humic material. The strong sorption is confirmed by observations of mercury levels in the sediments near Basel, which were about twice the normal background concentrations of Rhine sediments (9). The mercury should have a relatively long residence time in the sediments, but eventually will be transported down river by current action or biologically transformed to neutral organomercury compounds (i.e., methylmercury), which have the potential to be transferred to the water and to be bioconcenaated.
Current condition and conclusions Fortunately, this accident has not proved to be the long-term ecological disaster that was originally feared by some. However, problems of chronic chemical inputs remain and need to be examined and dealt with in a continuous and systematic manner. Within a few weeks or months the Rhine River had purged itself of all the pesticides from the fire (with the possible excep tions of mercury and endosulfan). There should be no residuals of these chemicals in the water, fish, or sediments. Some fish started to return to the Rhine at Basel in the spring of 1987. In the fall of that same yea-one year after the catastrophic accidentthe benthic fauna had recovered. With the exception of eels, the fish had reS96 Environ. Sci. Technd., MI. 22. No. 9,1988
NrIIed to even the
most affected places.
This quick recovery has brought the ecosystem nearly back to the situation that existed before the accident. However, the preaccident ecosystem was not highly &versified, for it was already severely affected by chronic chemical contamination. We need to learn from the Rhine River tragedy and uy to avoid other accidents that may have longer lasting effects. The suddenness and severity of chemical spills should be countered with fast reaction and remediation by environmental scientists. The ability to understand and predict the environmental behavior of a chemical is crucial to positive action and must be based on quantitative data (physical, chemical, and biological) describing environmental processes. Unfortunately, these data contain tremendous gaps, and much of the necessary information on the 20 Rhine River pesticides and a myriad of other toxic chemicals are not available in the literature. The data that do exist ax,at best, difficult to obtain and are often inadequate, incomplete, or conEicting. A data bank that stores environmentally useful information on anthropogenic chemicals should be made accessible so we would be better prepared to contend with and predict the outcome of the next ecological disaster and assess the impact of the chronic chemical pollution. Acknowledgment This article was reviewed for suitability as an ES&T feature by Richard G. Zepp, EPA Environmental Research Laboratories, Athens, GA 30613; and by James Leckie, Stanford University. Stanford. CA 94305.
References (I) Rich, V. Nature 1986,324,201. (2) Deininger, R. L. 1.Am. Water Wrkr As-
SOC. 1987, 79, 78-83. (3) First Report on the Ecological AssessmentandRecomrnendations for Measures and Funre Investigations Afer the Sandoz Accident in the Rhine River 01 Base1 (in German): Swiss Pederal InstiNte for Water Resources and Water Pollution Control: Diibendorf, Switzerland, 1986. (4) Anon. Environ. Sci. 2chnol. 1967, 21, c _I_
(5) hrermrionafCommission for the Proteetion of the Rhine against Conlaminarion-1985 Activig Report (in German); International Organization for the Protection of the River Rhine Against Pollution: Koblenz 2, Federal Republic of Germany.
(6) Meijers, A. P. In 2nrh Workshop of the Inrernarional WareRvorkr Association of the Rhine Warershed (in German); International Association of Waterworks in the River Rhine Against Pollution: Koblenz, Federal Republic of Germany, 1985; pp. (7)
97-117. Kiihn, W.: Clifford, D. Proceedings of the Wter Quofig 2chMfogy Confir-
ence; American Water Works Association: Denver, CO, 1985; p. 353. (8) Oreve, P. A,; Wit, S. L. J. Wter Poffur. Control Fed. 1971.43, 233848.
German Commission for Water Pollution Conlrol o f lhe Rhine River; German Repori m fhc Sondoz Accidcnf with Anolyticol Results (in German): International Organization for the Proteclion of the River Rhine Against Pollution: Koblenz, Federal Rcpubk o f Germany. 1986 The Rhrnr R ~ b r AJitr r rhc Pollution Evmr bv Gndoz 10" French). Counsel1 S u m r;eur de la 'Pkhe: Mbntinny les M k . France, 1987. Reichert. R; Wanner, 0. In Proceedings of the TwelJih Congress o the lnterna fionol Associalion of Ifydrnulic Re: search: Water Resources: Linleton, CO. 1987; pp. 239-44. Second Rcporf on the Behavior of the Chemicals in rhe Rhine River. Biolonicol Ccrndirions and R c c o w v of the thine Riitr A f i ~ the r Fire or Schveizerhallc (in German): S u i s Federal lnrlitute for Water Rebourccr and Water Pollution Control: Dbbendorf. Suitzerland. 1987
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Theory Paul D.&pel (1) is a chemisf wifh the U.S. Geological Survey k M e r Resources Division. He received his Ph.D. in environmental engineeringfrom fhe University of Minnesota in 1986and was a posfdocroml fellow at the Swiss Federal Institutefor Water Resources and Water Pollution Control (EAWAC).His research and reaching interests lie in fhe environmentalfate and transporf processes of contaminants and environmental chemodymics.
lihllrr Giger (r) holds a Ph.D. degree in chemisrryfrom the Swiss Federal Instifufe of Technology (ETH). He leads an EAWAC research group involved in environmental analysis and fare assessment of organic pollutants. Ciger teaches organic geochemistry and environmental chemistry af ETH and fhe University of Zurich.
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Peter ReicheH (1). a member of the system analysis group 01 EAWAC, received his Ph.D. in theoretical physicsfrom the Universify of Basel, Swifzerland. His research concentrates on fhe analysis of mixing ana fransport phenomena in rivers and on mathemnticai modeling of river quality. Oskar Wanner (r) is an engineer at EAWAG specializing in systems analysis and mathematical modeling. He holds a Ph.D. in nafural sciencesfrom fhe Swiss Federal Instilute of Technology in Zurich. His research topics include mixed population biofilm and river quality modeling.
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