Royal Swedish Academy of Sciences

Ixtoc I: A Case Study of the World's Largest Oil Spill Author(s): Arne Jernelöv and Olof Lindén Source: Ambio, Vol. 10, No. 6, The (1981), pp. 299-306 Published by: Allen Press on behalf of Royal Swedish Academy of Sciences Stable URL: http://www.jstor.org/stable/4312725 Accessed: 13/05/2010 11:42

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http://www.jstor.org the World'sLargest Oil

SpilleJ||| BY ARNEJERNELOV AND OLOFLINDEN

On June 3, 1979, the Ixtoc I exploratorywell in the Bay of , blew out. It was finally capped on March23, 1980, 290 days later,but during that time 475 000 metric tons of oil were spilled into the watersof the Gulf of . The full extent of the damage is still unknown.

On December 10, 1978,Petr6leos Mexica- Figure 1. Location of the Ixtoc I in the . nos (PEMEX) started to drill the Ixtoc I exploratorywell at longitude92?13'W and latitude 19'24'N, about 80 kilometers north-west of in the Bahia de Campeche(Figure 1). The water depth at the site is about 50 m. The drilling CorpusChristi --- continued through the first part of 1979 /__ and by the end of May a depth of 3600 a- _ meters had been reached. Early on June 2 CoMatasoCh at a depth of 3615 meters, the well started to loose drilling mud; circulation was totally lost about 3625 meters. Several un- as_ Sf /~~~~~ successful attempts were made to regain LaPsca, P rsl = , circulation, but as the well appeared 4t ME X C stable, it was decided to seal it by with- drawingthe drill pipe and insertinga plug TampCo?_ in the empty space. On June 3, duringthe LguaganeMoaleBrs G L attempts to seal the well, the extremely SW / high pressure (about 350 kg/cm2)caused FlF~~~~~~~~~~~~ Progres mud to flow up the drill pipe and onto the & ampico l platform.At 3:30am the well blew out and EHX IfC

caught fire. The explosion and fire des- Laguna de ueboVoioac troyed the platform, which sank to the ^~~~~~~~~ a bottom and damaged the stack and well CoatZacoalCF s~~~~~~~pL na e a ------0cCida = ~ ~~~ra4 lllTh : Ca casing. This allowedthe oil and gas to mix ~~~~~4 \/ zz V _ . u with water close to the floor, begin- -~~~~~~~t cm,~RFLanana>t Ba Ta ina Coa I- ~^i ~ ~~~ ~ ~ ~& ~ ~~~xo $ ning the largest marineoil spill in the his- sqW tory of oil exploration. Initially the spill was estimated to be z~~~A Asof about 4500 metrictons per day. However, by the beginningof August the well had lost over 225 000 metric tons-more oil than had been lost in any previous acci- dent involving offshore drilling or trans- portation. When the well was finally cap- ped on March23, 1980-290 days afterthe blow-out-a total of about 475 000 metric tons of oil had been lost, according to PEMEX estimates (1).

AMBIO, 1981 299 Figures 2a and b. The blowout as seen from a helicopter. Wind and current carried the oil in a north westerly direction. The rig in the foreground (left above) is a relief drilling platform. 2b on opposite page is a close-up of 2a. All photos: Olof Linden.

Figure 3. A thick layer of "chocolate mousse" close to the blowout. The oil that was lost during the blow- out polluted a considerable part of the offshore in the Gulf of Mexico as well as much of the coastal zone, which consists primarilyof sandy beaches and barrierislands often enclosing extensive shallow lagoons. A number of studies were intitiatedto assess the extent of the damage. One of these was set up by the United Nations Environment Program (UNEP) at the request of the Mexican government.A summaryof the results of that study (2), which focussed mainly on the acute impact of the spill, is reported here.

GENERALBEHAVIOR OF THEOIL The oil from Ixtoc I reachedthe at a depth of 51 m and was injected into the water initiallyat a pressureof 350 kg/cm2.

300 AMBIO VOL 10 NO. 6 LW I< f- JTI J

Figure 4. Booms and skimmers in operation. In the background can be seen another relief drilling platform. The oil was saturated with gas and conse- quently hit the surface as a three-phase t:~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ emulsion, water droplets and gas bubbles in oil, with a water content of about 50 percent. Due to the high pressure at which the emulsion was formed the droplets were small. Most of the gas was burned as it emerged but only a very small fraction of the emulsified oil was actually burned (Figure 2 a, b). The oil was of a light type. Thus, a high proportion consisted of straight-chain and cyclic hydrocarbons with less than sixteen carbon atoms, both comparatively vola- tile and water-soluble. During the first part of the blow-out, the emulsified oil formed a surface layer 1-4 cm-thick, 0.7-5 km wide and about 60 km long (see Figure 3). The initial formation of an emulsion re- sulted in the oil from the blow-out having

AMBIO, 1981 301 less contact surface with the atmosphere well. However PEMEX estimates that ab- early October. The theoretical pick-up and more contact surface with the ocean out 50 percent of the spilled oil burnedat capacity of the equipmentused was about water, compared with oil discharged on the well site (3). 20 percentof the total outflow, but a num- the water surface. Thus, considering its Mechanicalrecovery in the Ixtoc zone ber of obstacles meant that only 4-5 per- chemical composition, a largerpart of the removed 10000 metric tons, about 4-5 cent of the oil was actually recovered. Ixtoc oil was dissolved in the water and a percent (3). Evaporation,judging by data One major problem was the weather. At smallerpart evaporated to the atmosphere in the literatureand experimentswith the wave heights higherthan 3 to 4 meters the when comparedto other spills. actual oil which took into account its equipmentwas not operableat all; and the As the lighter fractions of the oil were physical and chemical characteristics, wind speed during the fall and winter in lost throughevaporation and dissolution, could have removed 45-70 percent. The particularfrequently caused wave heights and as the gas bubbles left the emulsion, initialemulsification was likely to result in higher than that. Another majorproblem the remaining part gradually became an actualfigure in the very low partof that was that it was not consideredfeasible to heavier. As more and more water was in- range. operatethe system at night. A thirdlimita- corporated in the emulsion, it gradually The fraction that went into solution in tion was the difficulty of rearrangingthe changedfrom water dropletsemulsified in sea water was generallyconsidered small. barges and booms as winds and currents oil to oil dropletsemulsified in water. Ow- It seems likely that less than 100ppm was changed. This caused part of the oil to ing to their surface stickiness, the oil actually dissolved and therefore the total driftpast each side of the boom configura- droplets accumulated particles from the amountis insignificantin this context. tions. And finally, the oil-collectingequip- water and thus gradually increased in Again taking data in the literatureas a ment used broke down on a number of density. Micro-organismsattached them- basis, it is thoughtthat biologicaldegrada- occasions. selves to the droplets and zooplanktonfil- tion, together with photochemical and In order to protect the lagoons from ter-feeders consumed both the droplets chemical breakdown during the acute being contaminatedby oil, booms were and the microorganisms, incorporating phase of the spill, would accountfor 10-15 placed across most of the inlets along the the oil residues in faecal pellets that in- percent of the oil. coast. Because of the way the booms were creased the sinkingrate of the oil. As the The oil on Mexican beaches that the deployed, however, they were seldom droplets increased in density, they gra- authors observed in early Septemberwas effective (Figure 5). Frequently the cur- dually sank throughthe water column. In calculated to be about 6000 metric tons. rent passing throughthe inlets either rup- the Gulf of Mexico there is a stratification Most of it had landed duringthe preceding turedthe booms or pressed them underor in the watermassdue to temperatureand/ four or five days. Based on reports from over the water. As a boom is normallyan or salinity. This stratification is partly various groups and individuals,five times effective barrieronly at velocities below caused by the influx of fresh water via that figure is thought to represent a fair 0.7 knots at rightangles to the boom skirt, rivers and lagoons. There are indications estimate of what had landed on Mexican the only way to use booms in most of the that partsof the Ixtoc I oil sank in droplets beaches. inlets would have been as deflectors throughthe less dense surface water and Investigations along the coast placed at a comparatively narrow angle temporarilyaccumulated and floated on show that approximately4000 metrictons againstthe driftingdirection. And the con- the stratawith higher density. Eventually of oil or less than 1 percent was deposited fined oil would have needed to be re- the oil increased in density and sank there (4). The rest of the oil, about 120000 covered using pumps or skimmers, with- through the denser water strata. If the metrictons or 25 percent, sank to the bot- out too much delay. This was not done. stratificationwas broken up due to wave tom of the Gulf. On June 9 large-scale dispersant action or changes in temperature,oil float- spraying commenced using specialized ing on the sub-surface layer could again fixed-wing aircraft.The dispersantswere reach the surface. THECLEAN-UP initially sprayed in a zone 10 to 25 miles When it reached a beach, the oil was off the coast, but later, during the fall, either deposited there, or made to sink in Ixtoc area dispersantswere also sprayedclose to the the shallow water, weighed down by the Operationsto combat the oil within the beaches, near the mouths of the lagunas, particulatematter in the zone where the Ixtoc I area were conducted from several and aroundthe well site. From late Octo- waves broke. The oil on the beach was auxiliary ships and barges. For confine- ber dispersant spraying from boats gra- exposed to sunlightthat raised its temper- ment of the oil, high sea booms were duallyreplaced sprayingfrom aeroplanes. ature and intensified weathering. It anchoredin fixed positions attachedto the The exact quantity of dispersantused in formed tarlike balls or cakes with little barges (Figure4). For recovery of the oil, the clean-up is not known. However, stickiness. skimmers and absorbent devices were according to information received by used (see Figure4). PEMEX (3), at least 9000 metric tons The recovery operations started in the were used. Of this, at least 6750 metric FATEOF THEOIL late part of June and were cancelled in tons were Corexit products (5). This From the start of the blow-out on June 3, 1979, to the final capping on March 23, 1980, a total of about 475 000 metric tons of oil was lost (1). Various attempts were made to stop the blow-out, and they grad- Table 2. Fate of the Ixtoc I oil during the acute ually reduced the flow-rate of oil (Table phase. 1). Percent Metric Based on data from the Ixtoc I case, Table 1. Oil released from Ixtoc I. Tons analogies with other oil spills and data in Period Daily Total Burnedat well site 1 5 000 the literature,an attempt has been made loss accumu- Mechanicallyremoved at (metric lated well site 5 23 000 to estimate the fate of the oil from Ixtoc I tons) loss Evaporatedto the atmos- (Table 2). The emulsification brought phere 50 238 000 down the amountof oil that was burnedat 3 June-12 August 4 400 300 000 Degraded biologically and 13August-15 November 1 500 438 000 (photo) chemically 12 57 000 the well site. The authors estimate that 16 November-30 November 600 447 000 Landedon Mexican beaches 6 29 000 only a very small fractionof the oil, prob- 1 December-5 March 300 475 500 Landedon Texas beaches < 1 4 000 6 March-14 March 60 476 000 ably less than 1 percent, was actually dis- Sank to the bottom 25 120 000 posed of when the gas was burned at the SOURCE:Reference 2. SOURCE:Ref. 2.

302 AMBIO VOL 10 NO. 6 t~~ ~ ~~~~~''I

Figure 5. Attempts to prevent the oil from entering the lagunas using booms often failed because of strong currents.

means that the use of dispersant during a weight of 1-2 kilogramseach. The balls cember. However, it was necessary to the Ixtoc I blow-out was one of the largest were forced into the well head but the high complete the other relief well before the in history. pressureof the leaking oil and gas ejected pressure was relieved. The Ixtoc IA About 30 000 metric tons, or about 6 them. However, using this method a sub- reached the Ixtoc I formation in the percent of the oil from Ixtoc I, landed on stantial reduction of the oil and gas flow second week of February. On March 23 the Mexican beaches of the Gulf (7). No was obtained in the middle of August the pressure of the mud that was pumped clean-up at all was carried out over large when the flow rate decreased from 10 000 through the relief wells and into the areas. Here, the oil was left for natural metric tons per day to about 4000 metric formation finally reduced the flow of oil degradation. However in some areas a tons per day, accordingto PEMEX (4). and gas to zero through the Ixtoc I well type of clean-up technique was used that Next a funnel-shapedoil collection de- head. After this was done, the well was involved covering the contaminatedsand vice a "sombrero", was placed over the sealed with several cement plugs. with clean sand; bulldozers dug a trench well in anotherattempt to reduce the flow some 1.0 to 1.5 meters deep and the oily of oil. The Sombrero weighed about 310 sand was then shovelled into the trench tons in the air, was 12 meters wide and 6 EXPOSEDOR THREATENED and buried. meters high. It was positioned with its ECOSYSTEMS wide end down above the well head in the middle of October. The oil and gas con- Offshore EFFORTSTO STOP THEFLOW OF OIL tained under it was pumped through a The continentalshelf, extending from the In late June, about three weeks after the flexible hose at the top to a platform. wide Campeche Bank in the east to the Ixtoc I blow-out, an unsuccessful capping However due to logistic problems at the narrowerbut longer shelf in the west and attemptwas made. The so-called blow-out platform,only a minor part of the oil that north,is flat and covered by fairlyuniform preventer, which consists of valves situ- could be recovered via the Sombrerowas sediments. These bottom areas form high- ated on the well pipe over the sea floor, actually disposed of. In the early part of ly favorableenvironments for diverse spe- was closed. The valves were situated Decemberrough damagedthe device cies of demersal fish, shrimps, molluscs, under the rupturedpart of the pipe and and it was removed from the well site. crabs and other invertebrates. had not been damaged by the blow-out. The measure that finally capped the Little study has been devoted to the fish However, the capping failed due to the well on March23 was the pumpingof mud populations but it is believed that they high pressurein the well, which caused oil into the relief wells Ixtoc IA and IB. The have a commercialpotential (biomass > 8 and gas to leak outside the well casing drillingof these relief wells was started in kg/hectare).However, at present they are below the blow-out preventer. the middle of June and the middle of July not being exploited to a very great extent. Several attempts were made to de- respectively. The first to be completed The shrimp populations on the con- crease the flow of oil from the well using was the Ixtoc IB. A link between the relief tinental shelf are large and commercially large numbersof steel and lead balls with well and Ixtoc I was established in De- very important, especially on the Cam-

AMBIO, 1981 303 Figure 6. The crab populations along several hundred kms of coastline were almost totally wiped out by the lxtoc I oil.

peche Bank and in the area of Tampico. The three major species are the pink shrimp, Penaeus duorarum, the white shrimp,Penaeus setiferus, and the brown shrimp,Penaeus aztecus. The total biomass of shrimp on the Campeche Bank was measured in one area near the Ixtoc I well at about 4 kg/ hectare. Of this, the white and pink shrimpcomprised approximately 37.5 per- cent each, while the pink shrimpmade up the remaining25 pecent, thoughin fishery statistics the latter account for 80-90 per- cent of the catch on the bank. Since 1964, the actual catch has been close to 15000 metrictons per year. Less is known about the shrimpstocks in the area of Tampico, but the present catch (1979/80) has been roughly calcu- lated by Pesca, the Mexican Department of Fisheries, at 6000 metric tons per year. Here the mainspecies is Penaeus aztecus. The pelagic ecology of the Gulf of Mex- ico is markedby high primaryproductiv- ity caused by nutrientinput from a num- ber of large rivers discharginginto it, and by upwelling that occurs in a number of places. Primaryproduction near has been measuredat as high as 5 g C/M2/ day. Pelagic fish stocks are thought to be considerable, although only a few are fished commercially: bonito, mackerel, sardineand other clupeids.

Coastal Coral Reefs There are two clusters of coral reefs along the western Gulf of Mexico, one situated north and east of Tuxpan, and the other east of Veracruz. The Tuxpan reefs form the most northerlycluster of reefs in the western part of the Gulf and are situated some 10-20 km from the coast. The Tuxpanreefs generallyhave a semi- lunar shape, with their major axes orien- tated north-south. Maximum develop- ment of the reefs occurs in the south-east sections, suggestinga strong influence by

Figure 7. Large and frequent plankton blooms occurredafter the blowout both off-shore and close to the beaches.

**,.

304 AMBIO VOL 10 NO. 6 the dominantcurrents from the south-east poorly sorted calcareous sediments and about 1800 km2 and two openings to the and by the periodic destructive cyclones shells. They are frequentlyinterrupted by sea. Brown and white shrimp from the from the north. The reefs rise from a rocky headlands and are much narrower Campeche Bank spend the early part of depth of some 25 m to not more than 1.5 m than the barrierbeaches. Prominentsand their life cycle in this lagoon andjuveniles and some have sandy bays rising above dunes are also absent. The fauna of these are fished commercially. There are large the water level. The average tides are beaches is also poorly developed. populationsof the oyster, Crassostreavir- approximately0.5 m and the maximum Human activity on the beaches varies ginica and the clam, Rangia cuneata, and 1.0 m. The Veracruz reefs have more or with the natureof the beach and its prox- both are exploited for commercial pur- less the same configurationas those near imity to towns and fishing areas. Along poses. It is clear that the lagoon is of great Tuxpan but occur in two distinct barrier the western shore, the barrierbeaches are importance to the shrimp stocks of the formationsaway from the coast: an inner used extensively for recreationnear major Campeche Bank and has a high potential and an outer. populationcenters (eg Veracruz,Tuxpan, for furtherfishery development. The structure of the reefs is roughly Tampico). However, away from these The Lagunade Tamiahuahas an area of similarto that found throughoutthe trop- centers, the beaches are generally de- about 700 km2with one opening to the sea ical Atlantic, and the communitiesassoci- serted, except for some fishing activity. at its southernmostpoint (Barrade Villar- ated with them are the same. Ernesto rea). It harborsdense populationsof Cras- Chavez has described the communities sostrea virginica, of which, according to occurring at Lobos reef, located 65 km Rockyshores the Pesca authorities, 25000-30000 met- north-eastof Tuxpan (6). Usually associ- Rocky shores are not very common along ric tons are harvested annually by 3000 ated with the reefs are seagrass beds the Gulf of Mexico and are found chiefly oyster fishermen.This lagoon is the major which harborextremely rich and produc- in the area south of Campechewhere they producer of oysters in Mexico and may tive communities on the leeward side, are formed from raised reefs and are ex- also be its most productive.In additionto protected against the open sea. These posed to the open sea. The fauna and flora oysters, juvenile white shrimp and two seagrass beds, dominatedby Thalassia or of these rocky headlandsare not very rich species of Mugil are fished. turtle grass, act as nurseriesfor commer- because of the high solar heat burdens. The Laguna Madre is a large complex cially importantspecies of fish and crusta- They are dominatedby small gastropods system of inlets, enclosed or semi-en- ceans. For example, the pink shrimp and encrusting algae. Subtidally, the di- closed lagoons, tidal flats, marshes and (Penaeus duorarum), the grass shrimp versity increases greatly. islands. Its total area is estimated at (Palemouetes pugio), the spiny lobster, approximately3200 km2. Productivity is the mud crab (Neopanope sp), and mol- high and oysters and shrimpare fished by luscs such as Lucina spp and Chione spp, Mangroves more than a thousandfishermen from vil- aboundin this area. Mangrove forests occur along the coast lages and towns scattered around the la- from the town of Campeche to north of goon. Birdlife in the LagunaMadre seems Celestun. They are comprisedof the com- the most abundantof all the lagoons, and Sandybeaches mon western Atlantic species, Rhi- several water birds (especially terns, gulls The Gulfof Mexico has two characteristic zophora mangle (red), Avicennia nitida and the endangered brown pelican) nest types of sandy beaches. The first type (black), Laguncularia racemosa (white) and feed within the system. along the entire western shore, are gener- and Conocarous erectus (button). The ally long and wide stretches of beach com- mangrovescover a wide zone inlandfrom posed of fine- to medium-grainedsedi- the water's edge (up to 30 km) and show Rivers ments of mixed calcareous origin. These the characteristic zonation pattern of In additionto the Lagunas, which tend to are exposed to the open sea and are these species. There is very little human be estuarine,there are several reasonably poundedby heavy waves. There are wide, penetration into these mangrove forests large rivers that discharge directly to the active surf zones and gently sloping swash and thus it is suspected that the stands are sea and have estuarine conditions near zones. The fauna of these sandy beaches mature and free from any destruction. their mouths. is fairly constant in species composition Althoughthe mangrove'sfauna could not The interrelationships between the but highly variablein numbers.The char- be carefullyobserved, it is safe to assume differentoffshore and coastal ecosystems acteristic species is the beach clam Donax that their primaryand secondary produc- are very important,as can be seen, espe- that makes its burrow above the swash tivity is very high indeed and that migrat- cially for freshwater run-off and lagoon zone but is active in both the swash and ing fauna, such as shrimpand finfish, use hydrology,nutrient condition and produc- surf zones, especially during the night. it as feeding grounds for part of their life tivity in the Lagunade Terminos. Similar- Other species were present duringthe in- cycle. ly, freshwaterrun-off directly by the riv- vestigations but only Donax occurred in ers and through the lagoons affects sur- very large numbers (approximately face sea currents and productivityin the 10000/M2 near Rio Bravo). It is well Coastallagoons Campeche area and plays an important known that the Kemp Ridly turtle, which The entire Mexican coast from Carmento role in determiningshrimp (and possibly may be on the verge of extinction, has one Rio Bravo is punctuatedby a number of some fish) migratorypatterns. In addition of its few remainingnesting sites along the coastal lagoons of which the three largest the dependence of the commercially im- barrierbeach at RanchoNuevo near Tam- and most important are the Laguna de portantbrown and white shrimp, at diffe- pico. In 1979, approximately10000 baby Terminos (Carmen), the Laguna de rent stages of their life cycles, on the turtles were removed from their nests Tamiahua(between Tuxpan and Tampico) marine and lagoonal systems is well near the high-tidemark by conservation- and the LagunaMadre (between Tampico known and demonstratethe integratedna- ists and transportedto the open sea to and Matamoros).These lagoons are char- ture of these coastal ecosystems. avoid the possibility of contaminationby acterizedby tWo features:each has one or oil. more corridorsto the sea through a nar- The second major sand beach type row openingacross the barrierbeach, and BIOLOGICALIMPACTS OF THEOIL occurs along shorter stretches of the each is relatively shallow (only a few In general, the oil from the Ixtoc I blow- coastline, especially in the area between meters at most). In some there are exten- out acutely affected the species and Ciudaddel Carmenand Campeche. Here sive intertidalmud and sand flats and all ecosystems in the Campeche Bay area the beaches tend to be shorter, more cus- are biologicallyvery productive. throughits chemical toxicity (in the vicin- pate, partly sheltered and composed of The Lagunade Terminoshas an area of ity of the well) and through its physical

AMBIO, 1981 305 properties (stickiness) in a larger area pact on the littoral crab and on the mol- affected the figures for landingsof fish in offshore and along the coast. Thorough lusc faunaof the beaches which were con- Mexican harbors, and therefore conclu- studies of the long-termbiological effects taminated. The populations of crabs, eg sive judgements based on statistics alone of the spill have either not been carried the ghost crab Ocypode quadrata, were cannot be made. The actual extent of the out in Mexican waters, or the results of almost totally eliminatedover a wide area damage caused by the world's biggest oil such studies are not yet available. A re- (Figure 6). The crab populations on cor- spill has yet to be determined. cently publishedstudy of the spill (8) does al islands along the coast were also re- not provide any answers to this question duced to only a few percent of normal either. Thereforewe will discuss some of about nine months after the spill. The the effects the spill could theoretically abundantbeach clams (Donax) as well as References and Notes have caused and give examples of direct other molluscs of the sand beaches did not 1. According to Petroleos Mexicanos (PEMEX) offi- observations of effects made by the au- exhibit any drasticmortality following the cial daily flow rate estimates, the total amount of oil lost from Ixtoc I was about 476 000 metric tons. thors in the field. spill. The figures are quoted eg in Oil Spill Intelligence The commercially important species In several places in the Veracruz area, Report, March 28, 1980. However, after the final capping of the well, another figure (430 000 metric and ecosystems affected by the chemical such as on the coral island Isla Verde, tons) was released by PEMEX as the total amount toxicity of the oil were mainlythe offshore dense mats of green algae were observed of lost oil. 2. This report is based on the findings of a mission to shrimp and fish populations. Shrimp covering hard substrates such as corals Mexico by the United Nations Environment Pro- spawning in Campeche Bay may have and rock formationsabout 10 monthsafter gram (UNEP) with the co-operation of FAO, been particularlyaffected. The pink and the blow-out. It seems likely that these IMCO and IUCN. The mission had the following composition: A Jernelov (Mission leader, UNEP), brown shrimps (Penaeus duorarum, P effects were caused by repeatedexposure R Engdahl (IMCO), 0 Lind6n (FAO), C Rees aztecus) have important spawning to the oil, but it is still questionable (UNEP) and B Wade (IUCN). The views express- ed in this report are not necessarily shared by grounds south and east of Ixtoc I. The whether they resulted from effects on the UNEP or the other UN agencies, nor by any of the eggs, and more particularlythe larvae, are herbivores (mainly gastropods) or governments involved. 3. Ing Garcia-Lara, Jefe de la oficina de Proteccion known to be sensitive to petroleumhydro- whetherthe sensitive balancebetween the Ambiental, PEMEX, private communication. carbons. When wind and currentpatterns algae and the coral polypes had been dis- 4. E R Gundlach, K J Finkelstein, and J L Sadd. changed in October, the oil slick moved rupted in some way. In the off-shore re- Impact and persistence of Ixtoc I oil on the south Texas coast. In Proceedings of the 1981 Oil Spill south and south-east, thereby increasing gion there have been indications of an Conference, American Institute, the threatto these stages and possibly also adverse impact on the base of the marine Washington DC, 1981, p 477-485. 5. Information given by G Lindblom in connection to juveniles and adults. Laboratory ex- food-chains. Unusually large plankton with the presentation of his paper at the 1981 Oil periments exposing larvae and adults of blooms have been observed in the con- Spill Conference in Atlanta, Georgia, March 2-5, 1981. other crustaceans, including shrimp, to taminated areas, possibly indicating eut- 6. Dr Ernesto Chavez, Jefe de Departamento de crude oil show that the acute toxicity rophicationeffects or that the zoo-plank- Ecologia, Escuela Nacional de Ciencias Biol6gi- levels are in the range of 0.1-10 ppm total ton communities might have been dam- cas, Instituto Polit6cnico Nacional, Mexico . 7. In early November, a covering of oil between 15 oil. If we assume that 0.1 ppm was the aged (Figure 7). This would very likely and 30 cm deep was reported from the western acute toxic concentration (Ixtoc I oil is affect the exploitable populations of fish shore of the Yucatan from Ciudad del Carmen to Progresso. The report was made by the US Coast particularlyrich in the highly toxic, low and shellfish. Guard (Oil Spill Intelligence Report, November boiling aromaticfraction); a mixing depth Such large plankton blooms were 16, 1979). 8. Informe de los trabajos realizados para el control of 25 m; a five-day persistency of the toxic observed north and west of Tampico in del Pozo Ixtoc I el combate del derrame de pet- oil fractions in the water solution; and a September 1979 and were very frequent roleo i determinasi6n de sus efectos sobre el required concentration of 0.1 ppm to on and aroundthe CampecheBank in the ambiente marino. Programa Coordinado de Estu- dios Ecological a la Sonda de Campeche 1980. cause damage to shrimps, as well as to beginningof 1980. 9. Oil Spill Intelligence Report, January 4, 1980. planktonor other pelagic organisms;then Fishing was bannedor restrictedby the 10. Dr Carranza-Frazer, Director General del Institu- an area of 15000 km2 can be regardedas Mexican authorities in several severely to Nacional de Pesca, private communication. poisoned by the Ixtoc I oil. This is equal contaminated areas north and south of to 2.5 percent of the Mexican part of the Tampico in September. Fish and octopus Gulf. catches reportedlydropped by 50-70 per- The amountof oil that reached the bot- cent from the 1978 levels off Port Mans- Olof Linden,Ph D in Zoological Ecolo- tom sediments of the Gulf is estimated to field and Port Isabel, Texas, and off the gy from the University of Stockholm, be of the order of 120000 metric tons (see Mexican coast from the US border south is responsible for the marine biology Table 2). Offshore, this oil was mostly in to La Pesca (9). The overall statistics for and oil pollution research programs the form of small droplets, with larger landingfigures for 1979 and 1980 indicate at the Swedish Water and Air Pollu- aggregates sometimes forming nearer the that no decrease in the amountof fish and tion Research Institute (IVL). He is shore. The averageconcentration over the shellfish landed in Mexican harbors consultant to the United Nations entire area would have been below 1 g/m2, occurred, compared to figures for 1979 agencies FAOand UNEP on environ- which is not considered high enough to (10). However the fishery statistics are mental impact of oil and heavy metal cause substantial damage to the benthic not a reliable indicator of damage to the pollution. His address: Swedish Wa- ter and Air Pollution Research Insti- ecosystem. The shrimps'habit of burrow- fish populations. Shifts in landing places tute (IVL),Utovagen 5, S-371 37 Karl- ing in sediments and consuming them by individualboats, which are impossible skrona, Sweden. could have resulted in the uptake of pet- to see in the statistics, may have drastic Professor Arne Jernelov was born roleum hydrocarbonsand tainting of the effects on the landingfigures, and changes in 1941 and received his Ph D at the shrimps. in foreign nations' fishery concessions University of Stockholm in 1966. He There was a lot of concern about the would distort the figures on total catches. came to the Swedish Water and Air damagethe oil might cause to the ecology For example, Mexico excluded foreign Pollution Research Institute (IVL)in of the shallow coastal lagoons. As it fishing over her shrimpfishing groundsin 1967, where he became its chief turned out however, very little oil was 1979. Another shortcoming is that new biologist. For a couple of years he actually spread into the lagoons. It was was a senior scientist at WHO in species, previously not included in the Copenhagen. In 1975 he returned to preventedmainly by the waterflowing out statistics, may affect the total figures. For IVL to become its director of re- of them; a flow that was increased by the instance, octopus landingswere included search. His address: IVL,Box 21060, unusuallyheavy rains duringthis particu- in the catch figuresfor the first time in the S-100 31 Stockholm, Sweden. lar winter. years following the blow-out. There are It is clear that the oil had a drastic im- indications that all these factors have

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