Oil Pollution Studies on Lake Maracaibo, Venezuela

OIL POLLUTION STUDIES ON LAKE MARACAIBO, VENEZUELA

W.L. Templeton, E.A. Sutton, R.M. Bean, R.C. Arnett J. W. Blaylock, and R.E. Wildung Battelle Memorial Institute Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 Pacific Northwest Laboratories Richland, Washington and H.J. Moore Creole Petroleum Corporation Caracas, Venezuela

ABSTRACT 4. Determination of toxicity of oil on selected aquatic organisms by laboratory bioassay. The results of a 2-year study on the impact of oil discharges on 5. Assessment of the probable and potential impacts of oil, oil the fishery resources of Lake Maracaibo, Venezuela, are presented. compounds, industrial and domestic waters on the fishery The lake system is described, together with relevant water quality, resources of Lake Maracaibo. hydrographic, ecological, and fishery resources data. Sources of Lake Maracaibo (between 9° and 11° north latitude) lies in a other types of pollution, domestic and industrial, are described, and basin surrounded on three sides by mountains which reach a maxi- their potential impact on the system are discussed. Analysis of envi- mum elevation of 5,000 meters. The lake is connected with the sea ronmental samples-water, sediments, and biota-showed low con- through the Straits of Maracaibo. The shores of the lake are low, centrations of oil in lake water and no detectable accumulation of flat, and often swampy. The northern section of the basin is arid petroleum-derived hydrocarbons in muscle tissue of selected com- and is drained by streams which flow only in the wet season. The mercial species. The occurrence of bituminous materials in the sedi- southern section receives heavy rainfall, and a large number of ments, particularly in the oil production area, suggests that the streams drain the low coastal belt. Larger rivers arise in the moun- natural processes of volatilization, biodegradation, and sedimenta- tains and flow through marsh and swamp areas to the lake. tion are the major mechanisms for the removal of oil from the The lake surface is 12,013 km2, about 14% of the basin area. surface waters. Laboratory studies on the toxicity of oil indicate The lake is 150 km long, 110 km in maximum width, and has an that relatively high concentrations of oil are required to cause average depth of 25.9 m (figure 1). The lake bottom is essentially mortality. Extraction of oil with lake water, however, indicated that smooth with maximum depths varying from 24 m to 30 m in a concentrations of total light aromatic fractions were toxic in the central area. The deepest part of the lake lies 13 km off La Ceiba. parts per million range. The rapid loss, in a few hours, of light The annual rainfall varies greatly with distance from the coast, hydrocarbons from surface films of oil to the atmosphere was being about 57 cm at Maracaibo and 257 cm at the Catatumbo shown to reduce the toxicity to organisms significantly. Examina- Valley. The wet season extends from April to November. The tion of the limited fisheries data available does not suggest that the temperature of the lake water is relatively constant. The epilimnion resources are being depleted. However, consideration of the poten- only changes about 1.8°C in the course of a year, ranging from 29°C tial impact of nonpetroleum wastes indicates that they are contrib- in February to 30.8° C in September. The hypolimnion has slightly uting to the degradation of the water quality which, if unchecked, lower temperatures (28.4°C to 29°C). may subsequently reduce the biological resources of the lake. Studies in 1954 [1] indicate a close relationship between the annual cycle of rainfall on the basin and the exchange of water INTRODUCTION between the lake and the sea. It would appear that substantial quantities of seawater enter the lake during the dry season. In 1971 a program was initiated to study the effects of oil discharges on the fishery resources of Lake Maracaibo, Venezuela.1 Since this was the first major ecological and pollution study con- Ecological characteristics of the lake ducted in the lake, an evaluation of the potential impacts of domes- Water quality. tic and industrial wastes were incorporated in this study. The overall The salinity patterns of the lake have been objectives then were: described previously [1,2]. These studies showed that surface salin- ities at that time were about 1-2 parts per thousand (%o). Measure- 1. Acquisition of baseline data on water quality, primary pro- ments in 1973-1974 comfirmed a seasonal cyclic increase in salin- ductivity, macrofauna, sediments, and fishery resources of ities of surface waters from about 2.0 to 3.8 %o from January to the lake to establish the ecological characteristics of the lake. August. 2. Acquisition of data on the major sources of industrial and domestic wastewaters discharged to the lake. Subsurface samples in 1973-1974 confirmed a body of high salinity water greater than 6.0 %o at 25 meters depth, resulting 3. Determination of low levels of oil and oil compounds in from the intrusion of saline water through the straits in the dry water, sediments, and organisms. season (figure 2). Nutrients increased in this layer of dense water from August through November but were slowly eroded by the 1This program was supported by Creole Petroleum Corporation, overlying freshwater. The formation and persistence of this Caracas, Venezuela. hypolimnion apparently varies from year to year and is a function

489 490 CONFERENCE ON PREVENTION AND CONTROL OF OIL POLLUTION

determined by the 14C method indicated that the lake is probably the most productive body of water in the world with values greater than 3 grams carbon fixed per square meter per day. The population and density of the phytoplankton community are lower and less diverse in the summer-fall than during the winter-spring period. The blue-green alga Anacystis cyanea dominated in the 25 species identified. Zooplankton. The species composition of the zooplankton was not rigorously determined, but of the cladocera, the primary orga- nism was Moina spp. The primary copepod in the samples was Acartia tonsa. The primary rotifier was Brachionus spp. with two distinct species occurring. Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021

72°00 71°30 71°00

KHOMETCIS

Figure 1. Map of Lake Maracaibo showing oil producing areas of the seasonal distribution of rainfall in the basin [3,4]. It appears that the nutrients are trapped in this system until late in the year when they are mixed with the epilimnion.

Analyses for phosphorus and nitrogen demonstrated the pres- 0 10 ence of substantial concentrations of both elements in the water KHMKTERS with the highest concentrations in surface waters located near the populated areas. The mean winter values in surface waters were 40 Figure 2. Salinity (%o) at 1 meter above the bottom (September Mg/C phosphate-phosphorous and 180 ng/Q. ammonia-nitrogen. The 1973) phosphorous concentrations in the surface water are several times higher than were measured in the mid-1950s [1]. Benthos. The scarcity of benthic flora and fauna are notable in Lake Maracaibo. Rooted plants and periphyton were not observed Current patterns. In March 1974, current velocities were in the main body of the lake. The benthos is comprised of small measured at 23 stations in the lake with a modified version of the polychaetes and extremely small snails, and at one station three Chesapeake Bay Institute Drag [5]. The magnitude and direction of small clams were found. The paucity of plants and animals is not the current are basically in agreement with previous data [ 1 ]. The surprising since the sedimentary substrate consists of a fine, uncon- rotary circulation of the lake causes the dense water of the hypo- solidated material. limnion to form a cone with its apex at the vortex of the eddy [ 1 ]. This vortex lies east of the geographical center of the lake. While Fisheries. The exploitation of fisheryresource s of Venezuela had previous investigations showed only a two-layered system [ 1 ], later received little study before 1967. By 1972, considerable progress work [3] showed a complete mixing of the system in late winter was made in stock assessment based on the analysis of catch and and spring with the reformation of the hypolimnion in the dry effort data. However, for Lake Maracaibo only total landing data is season upon reentry of salt water. During the present study, a com- available. No effort data, except for the shrimp and crab fishery, pletely mixed lake was found in January 1973 when no evidence of have been collected. a hypolimnion could be found and again on March 28, 1974, when The greatest density of fishingboat s and fishermen in Venezuela the last traces of the hypolimnion were observed. is found on the shores of Lake Maracaibo. The major concentration of fishermenan d boats are in the districts adjacent to the Straits of Plankton. The primary trophic level of this system is comprised Maracaibo [6,7]. About 20 species contribute significantly to the almost entirely of free-floating microscopic algae. The overall landings from the lake itself. abundance of phytoplankton was determined by measuring the Shrimp are the most valuable fishery resource in Venezuela. In chlorophyll-a content. The maximum concentration was observed in Western Venezuela, the white shrimp (P. schmitti) apparently forms January at nearly all stations, with the highest values (>200 vg one stock only, with the juveniles in Lake Maracaibo and the adults chlorophyll-a/C) along the northeast coast in the straits. The in the Gulf of Venezuela. Shrimp catches from the lake constitute timing of the maximum correlates with the period of complete about 15% of the total catch in Western Venezuela. Of the finfish in mixing in the lake; hov/ever, the distribution is also influenced by 1972, about 40% of the finfish landing consisted of lake curvina the overall current flow patterns. Values for primary production (Cynoscion maracaiboensis). Other important commercial species EFFECTS 491 are Manamana (Anodus laticeps), Bocachico (Prochilodus sp.), and the migration of shrimp and other commercially important fish catfish {Pimelodidae). species in the lake. The available fisheries data indicate an overall increase in land- One of the major toxic material discharges was identified at two ings with time; however, with the exception of shrimp and crab, thermoelectric power plants operating on the lakeside. In addition catch effort is not available. to the heated water, a toxic chemical, sodium pentachlorophenate, is discharged. This material is used as a biocide to reduce biological Municipal and industrial wastes fouling in the cooling systems. Toxicity tests conducted with commercial species of fish and shrimp in plant effluent showed this The characteristics and volume of domestic and industrial waste material to be extremely toxic, even after substantial dilution with discharges were evaluated in order to assess the potential impact on lake water. In order to reduce the concentration discharged from a the lake system (figure 3). Domestic wastes from a population of 250-megawatt plant to a nontoxic concentration of 0.2 ppm, a dilu- more than 1.5 million are discharged into the lake, and almost with- tion with 1/10 to 1/20 of the total water passing per day through out exception, no treatment is applied prior to discharge. The the Straits of Maracaibo would be required. Remedial action has population and waste characterization data indicate that substantial already been taken at one of these plants. quantities of nutrients and organic materials are discharged. The Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 approximate annual values may exceed 11,000 tons carbon, 1,400 Fate of oil tons phosphorus, and 5,500 tons of total nitrogen. These large inputs contribute to the extensive algal blooms, the limiting nutrient In the 60 years since commercial petroleum operations in the being nitrogren. Additionally, bacteriological measurements of shore Lake Maracaibo Basin began, Venezuela has become one of the waters of the populated areas show values which exceed accepted world's leading oil producers. The production available from Lake U.S. standards for both total coliform and fecal coliform. Maracaibo alone is estimated to be about 2,500,000 barrels per day. In view of the magnitude of these operations, some discharges of petroleum into the lake waters are inevitable from pipeline breaks and other incidents related to production and transport operations. Data are available regarding the sources, numbers, and volumes of oil spilled or discharged [4], with an estimated 100-120,000 barrels released in 1972. There is no question that large spills of oil into aquatic environments can cause localized adverse effects. This has been well documented by a number of investigations into the

RIO PUEBLO VIEJ0 effects of large oil spills on marine coastal communities in other TIA JUANAX parts of the world. However, the problem of determining the ^CIUDAD 0JEDA long-term effects of petroleum discharges on the overall aquatic RIO MIS0A ecosystem of Lake Maracaibo is more difficult. Long before explora- p BACHAQUER0 tion for oil was contemplated by man, the lake was exposed to "pMENE GRANDE petroleum contamination through natural seeps. In addition, there RI0M0TATAN exists no relevant baseline chemical or biological data from early or RIO BARUA preproduction eras against which to compare present day results. TRUJILL0 Thus, it is not possible to quantitatively relate the influence of petroleum discharges to environmental change. However, it is highly desirable to qualitatively estimate the effects of petroleum on the lake ecosystem and to compare them with other factors only indi- rectly related to the petroleum industry, such as rapid industrial growth and population increase. The studies on the fate of oil were designed to assess the levels of petroleum and petroleum-derived hydrocarbons present in the water column, the sediments, and the biota of Lake Maracaibo. For this purpose, 33 field stations were established along six transects for the ■ 3,000-4.999 INHABITANTS D 5,000-9,999 INHABITANTS collection of samples of water, biota, and sediments (figure 1). O 10,000-24.999 INHABITANTS Concurrent with the analyses of field samples, laboratory studies • 25,000 -99,999 INHABITANTS E3 MORE THAN 100.000 INHABITANTS were undertaken to measure the effects of oil and oil components T INDUSTRIAL ORGANIC DISCHARGES on lake biota of commercial importance. These studies were more a THERMOELECTRIC PLANT DISCHARGES A REFINERY OR PETROCHEMICAL PLANT DISCHARGES comprehensive than standard bioassays. They not only attempted to V ADDITIONAL INDUSTRIAL DISCHARGES quantify, but also to identify and characterize the properties of the toxic components of petroleum in order to obtain an estimate of the probable effects of these on the aquatic environment. The devel- Figure 3. Population centers and important industrial discharge opment of sensitive, highly sophisticated methods for hydrocarbons points in the Lake Maracaibo basin in water, biological tissues, and sediments represented a significant portion of this program. The methodology has been previosuly discussed in detail [8,9], and only the results of the application and Industrial wastes from tanneries, meat rendering plants, brew- their methods will be discussed in this report. eries, distilleries, dairy and food processing plants in the Maracaibo City area discharge substantial quantities of organic material, nutri- Extractable organic material and hydrocarbons in the water ents, and, to a lesser degree, toxic materials into the Straits of column. The waters of Lake Maracaibo were periodically sampled Maracaibo. Data collected in the straits indicated that a substantial over a period of 7 months from September 1973 to March 1974 at portion of the sewage discharge settles toward the bottom into the 27 locations. Samples taken at 1 m depth and 1 m from the lake saline water moving towards the lake. Near anaerobic zones were bottom were initially extracted with carbon tetrachloride, and the detected near the bottom in the straits and the northern part of the total extractable organic material was determined using infrared lake. These oxygen depleted zones persisted during the wet season spectro photometry. despite the net flow out of the lake in the wet season. Anaerobic More than 90% of the samples contained less than 1.0 ppm of areas were also detected offshore in the southeast area of the lake as extractable organic material. Samples taken at 1 m depth and con- a result of indirect discharges, via rivers, of milk processing plants, taining more than 0.5 ppm extractable organics were subjected to agricultural return water, and a sugar processing plant. The presence detailed investigation. The procedure was to chromatograph the ex- of these low-dissolved oxygen zones, particularly in the Straits of tract on deactivated silica gel [10], followed by gas chromatograph Maracaibo, is of particular concern since they may be a barrier to (GC) investigation of the separated fractions. 492 CONFERENCE ON PREVENTION AND CONTROL OF OIL POLLUTION

The data obtained on the water extract fractions indicate that the bulk of the material is more polar than either saturate or aro- • ROBALO matic hydrocarbons since it requires methanol, a very polar solvent, O CURVINA ^ V^ to elute most of it from the gel column. The amount of saturate ■ LISA ^~\^ material recovered was never greater than 15% of the total, and A MANAMANA \ 0.8 there was no GC evidence of any material in the aromatic fraction. 18 SPECIMENS] These results are in agreement with the findings of other investiga- ▲ BOCACHICO NT)*""^ 4.6 av tions which indicate that most extractable organic material in water ► SHRIMP 0-0 ^^3 is not hydrocarbon in nature [11]. (CONCENTRATIONS IN PPM) fu^J

The chromatograms of polar fractions generally show the pres- SKI •K ence of a variety of high-boiling material. The data obtained on the polar material does not permit a definite conclusion as to its compo- [3 SAMPLES] "^■"x/ °^V v 1.4 av sition, other than that it consists of a multiplicity of high-boiling, y polar components. Due to the high primary productivity of the lake, it is reasonable to presume that much of it is not bituminous, but 2.8 \J Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 rather is composed mainly of plant-derived pigments and lipids. This \ [2 SAMPLES] is consistent with observed carbonyl absorption in extracts. The 69av 1 \ A FISH FROM OUTSIDE LAKE MARACAIBO presence of some petroleum material in the extracts cannot be ruled \ ▲ out, particularly in view of the frequent observation of bituminous ^ 384 TROUT (MERIDA HATCHERY, VEN) particles floating in the water column. ^W 2 SAMPLES 2.3 ppm av In a related study, two samples of the blue-green algae Anacystis ^V PERCH (GRAYS HARBOR, USA) <^fS [4 SAMPLES] 2 SAMPLES 1.1 ppm av cyanea, which is a predominant species in the lake, were analyzed 04av for hydrocarbon content. One sample was taken from an oil pro- 1 •* ;( SEA TROUT (GALVASTON BEACH, USA) 2 SAMPLES 2.0 ppm av ducing area and the other from a non-oil-producing area. The hydro- CT^ carbon compounds found in both samples were similar. The few ) ^^ bOCACHICO (LOCAL POND) 2 SAMPLES 11.8 ppm av hydrocarbons detected had properties consistent with alkanes which are normally found in these kinds of plants and which are believed to be formed biosynthetically. No other alkanes or naphthalenes of Figure 4. Analysis of tissue samples for total hydrocarbon (gas chro- petroleum origin were found. matography) These studies thus suggest that the bulk of the extractable organic material is not hydrocarbon in nature. There has been no evidence of the lighter aromatic hydrocarbons (naphthalenes) which contained 0.18 and 0.13 /ug/g tissue of total n-alkanes. In addition, are typical of petroleum and have a higher degree of water solubility the total hydrocarbon content of the lisa samples was approxi- than other constituents of oil. The rate of disappearance of light mately 3 to 20 times higher than the total hydrocarbons found in hydrocarbons introduced into the waters of Lake Maracaibo from the curvina. Samples of lisa from areas free from oil production oil discharges is probably very high with respect to other bodies of could not be obtained. water because of the elevated temperature (30°C) and the high The highest concentrations of hydrocarbons from fish tissue potential for microbial activity in these waters. analyzed were found in the bocachico (38.4 jug/g) and manamana (11.3 Mg/g) which are restricted to the south end of Lake Maracaibo Hydrocarbon content of fish and other organisms. Samples of because of a low salinity preference. Because of the very high value commercially important species were examined for hydrocarbon for total hydrocarbons found in the bocachico, two samples were contents with two principal objectives: first, to determine if petro- obtained from a pond fed from waters having no relation to those of leum hydrocarbons were accumulated in the tissues of fish obtained Lake Maracaibo and having no contact with petroleum. Again the from the lake; and second, to identify the types of hydrocarbons in total amount of hydrocarbons found in these species of fish was the fish tissues. Samples of fish muscle tissue representing 6 dif- quite high with respect to other species analyzed (11.1 and 12.5 ferent species from the lake were analyzed for n-alkanes, methylnaph- Mg/g). Although the total quantities of hydrocarbons in each of the thalenes, total saturate hydrocarbons, and total aromatic hydrocar- samples from the pond were less than those found in the lake bons. The results were compared with analyses of fish samples from sample, the content of saturate hydrocarbons corresponding in re- other Venezuelan waters and from North American waters. tention time to n-pentadecane and phytane were higher for the Twenty-four fish from the lake were compared with 8 fish obtained pond samples than the lake sample. from other areas which were relatively oil free. The fish samples obtained from Puget Sound, Washington, Curvina (Cynoscion maracaiboensis) was intensively studied Galveston Beach, Texas, and the Merida fish hatchery, Venezuela, because of its relative abundance and commercial importance. This did not contain detectable concentrations of n-alkanes or meth- species had the lowest hydrocarbon content, averaging less than 1.0 ylnaphthalenes. The two trout contained larger concentrations of ppm total recoverable hydrocarbons. Other species from the laker total hydrocarbons than the curvina and robalo. listed in order of increasing hydrocarbon content of the muscle The individual alkane compounds found in tissue samples in- tissue, were robalo {Centropomus ensiferus), lisa (Mugil curema), cluded the naturally occurring pristane, and possibly phytane. white shrimp {Penaeus schmitti), manamana (Anodus laticeps), and Previous investigations conducted by Battelle-Northwest dealing bocachico (Prochilodus r. reticulatus). It was anticipated at the with exposure of fish to crude oil and refined products have shown outset that the hydroairbon levels present in Lake Maracaibo that tissue uptake of hydrocarbons from crude oils include both environmental samples would be considerably lower than in samples n-alkanes and methylnaphthalenes [12]. It is, therefore, significant subjected to lethal concentrations of petroleum hydrocarbons. that no detectable amounts of methylnaphthalenes have been found Therefore, rather elaborate methodology was developed during the in any Lake Maracaibo fish analyzed to date. Failure to detect course of this program which permitted the detection and quantita- methylnaphthalenes in fish samples containing paraffins suggests tion of h-alkanes and methylnaphthalenes at levels of about 7 and 4 that n-alkanes arise in the lipid pool as a result of normal metabolic ppb, respectively, representing an extension of previously reported processes rather than exposure to petroleum. work [12]. The map (figure 4) summarizes the results of analyses An interesting characteristic of gas chromatographic scans of the obtained in terms of species studied, location of catch, and total tissue samples is the similarity of patterns obtained on samples ex- quantities of hydrocarbons detected. tracted from the same species of fish, while larger differences were The total hydrocarbon concentration in curvina tissue from observed when the same fraction from different species are com- seven different stations did not indicate any trend that would corre- pared. Each species examined gave a characteristic and reproducible late with the oil-producing areas. There were no detectable concen- chromatographic "fingerprint," regardless of the location of sample trations of n-alkanes or methylnaphthalenes in any of the curvina or origin. The differences in scans obtained among different species robalo samples ai ed. Lisa obtained from the oil-producing area were likely a result of differences in diet and metabolism. EFFECTS 493

An additional study was conducted to evaluate the possibility of using mass spectrometry as a tool to identify polynuclear aromatic hydrocarbons in the tissue extracts. The results were disappointing in that limits of detectablility for individual compounds were found to be in the vicinity of 0.25 Mg- Considering that recoveries of polynuclear aromatic hydrocarbon from tissue samples were found to range from 20% to 50%, a reasonable estimate for the minimum detectable amount of an individual polynuclear hydrocarbon compound would be on the order of 0.1 to 0.25 parts per million. This value is rather high when compared to other methods for detecting specific polynuclear hydrocarbons; hence, only seven samples of aromatics fractions extracted from tissue were analyzed. These samples represented carbon tetrachloride extracts from robalo, lisa, perch, and Merida trout, and hexane extracts from manamana, bocachico, and shrimp. No molecular ions corresponding to molecu- Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 lar structures of polynuclear aromatic compounds were found in the mass spectra of any of the samples analyzed. The type and amount of total hydrocarbons found in the tissue samples appears to be more a function of the species of fish than the location from which they were obtained. This is in agreement with measurement of stable carbon isotope ratios. The relative abundance of carbon-13 in the samples was more closely related to the species of fish than sample origin, again suggesting that carbon derived from petroleum has contributed little to the carbon cycle of the aquatic population. Organic composition and hydrocarbon content of the sediments. Oil discharged into Lake Maracaibo is dissipated through evapora- tion, solubilization, and bacterial degradation. However, bituminous residues of petroleum discharges may eventually become part of the organic materials in the lake bottom. It is therefore not surprising that observations of bituminous particles in the sediments of the lake were a frequent occurrence. In 15 dredge samples subjected to chemical characterization, two taken off the northeast shore were 72°00 71°30 71°00 found to contain numerous bituminous particles ranging from 2-4 0 10 mm in diameter. KILOMETERS Lake Maracaibo sediments are rich in organic material. Samples Figure 5. Precent extractable organic material in Maracaibo core have been examined which have extractable organic contents as high sediment samples as 3% of the dry weight of the sediment, although may samples have lower amounts on the order of about 1%. It is, however, difficult to saturate fractions of crude oils, it is apparent that any organic mate- assess the relative contribution of petroleum discharges to the total rial in the sediment samples arising from petroleum has been exten- organic content of the lake sediment because it is the areas of in- sively altered. There was reasonable agreement between gravimetric tense oil production that also are affected by heavy plankton loads and gas chromatographic determinations of the saturate and and by large volumes of industrial and domestic wastes. aromatic fractions investigated, indicating that little nonvolatile In order to assess the contribution of petroleum hydrocarbons to material was present in these samples. the organic composition of the sediments, over 40 lake sediment Saturate and aromatic fractions from core and dredge sediments core and dredge samples were taken from widely separated geograph- were analyzed for hydrocarbon types using a high voltage technique. ical locations. Both types of samples were frozen at the site of Saturate hydrocarbons are identified according to number of collection and maintained in a frozen state until they were freeze- naphthenic rings, and aromatic hydrocarbons are identified accord- dried prior to analysis. The total organic extract (benzene-methanol) ing to the number and arrangement of aromatic nuclei. Analyses was obtained, and was further divided by solvent treatments into were performed by Petroleum Analytical Research Corporation, asphaltene-free extract and benzene-soluble asphaltenes. The Houston. Although there are several potential sources of error using asphaltene-free material was further separated by liquid chromatog- this technique [13], the aromatics analyses for the sediment frac- raphy into saturates, aromatics, and polar (NSO). tions appear to be consistent with that for crude oil residue. There The quantity of organic material extracted from the sediment are very low relative values for naphthalene types in most of the core samples indicated a general trend toward higher organic con- samples analyzed, including the South Tia Juana medium crude oil tent in the northern sampling areas. Statistical analysis of the data residuum. Naphthalenes are usually a predominant compound type from the set of core samples taken at stations above the dashed line in most petroleums. The surprisingly high relative values for benzo- in figure 5 were different from the rest of the samples with respect thiophenes and dibenzothiophenes in the South Tia Juana residue to total organic extract, benzene-soluble asphaltenes, and the per- indicate that the relative values reported for the aromatic compound centage of saturates in the asphaltene-free extract. types may be somewhat in error. Despite apparent difficulties, the The data also shows that the quantity of organic material ex- data obtained give at least a qualitative picture of the aromatic tracted, as represented by the benzene soluble asphaltenes and composition of the organic material in Maracaibo sediments, and asphaltene-free extract, tends to increase in this region, as does also suggest a close similiarity in composition to the compounds percentage of saturates in the asphaltene-free extract. The average found in petroleum bitumens. molecular weights of saturate, aromatic, and polar fractions all in- Graphical presentation of the saturate compound-type distri- crease in the oil-producing zone. The relative amount of sulfur butions determined for the sediment dredge samples is given in decreases in the aromatics fraction and increases in the NSO fraction figure 6. Of the 10 core samples, 6 have a predominance of 2-ring as the distance from the oil-producing zone is decreased. compounds; for the dredge samples, 7 out of 15 have this pattern. A These trends are consistent with the observations of an increase less frequently occurring pattern is that in which 1-ring compounds in both the absolute and relative amounts of bituminous residues in predominate; 2 core and 2 dredge samples have this compound type sediment samples taken during the benthic surveys. Using gas preference. Interestingly, only 3 of 25 samples had a clear pre- chromatography, n-alkanes were not detected in any of the saturate dominance of paraffins (no rings), particularly since the saturate fractions examined. Since these compounds predominate in the pattern determined for South Tia Juana medium residue, in which 494 CONFERENCE ON PREVENTION AND CONTROL OF OIL POLLUTION

Effects of oil Toxic effects of oil on fish, shrimp, and plankton. The toxicity studies conducted at the Las Morochas Laboratory were designed to 0 12 3 4 5 6 0 12 3 4 5 6 0 12 3 4 5 6 answer a number of questions regarding the toxicity of petroleum to NAPHTHENIC RINGS NAPHTHENIC RINGS NAPHTHENIC RINGS the aquatic biota of Lake Maracaibo. Initially, the determination of concentration levels of crude oil was required to induce mortality in commercially important species. It was also important to describe the factors which contribute to acute toxic effects and assess the relative importance of these factors when actual discharges of oil into the lake occur. Thus, experiments designed to evaluate 24-hour median tolerance limits (TLm24) of Lake Maracaibo organisms were accompanied by studies to determine the effects of "weathering" of crude oils on the resulting toxicity of the oil. In addition, laboratory comparisons between the toxicities of light and heavy crudes were Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 made, and the long-term effects of repeated exposures to crude oil studied. The oils used were from Lake Maracaibo. An important variable influencing the toxicity of oil in water was the type of agitation used to mix the oil with the water. Thus, a gentle agitation of an oil-water mixture at 10,000 ppm induced no toxicity, whereas an identical mixture was highly toxic when agitated for 10 minutes with a magnetic stirrer. The viscosity of the test oil was also an important variable under the experimental conditions used. Tia Juana light crude was mixed poorly with lake water, resulting in erratic toxic responses and no evident correlation between the amount of oil added and toxicity. Tia Juana heavy crude mixed well with water but imparted less toxicity than Tia Juana medium crude. Most of the acute toxicity experiments were conducted using a static bioassay procedure. A given amount of oil was agitated with lake water for 10 minutes using a magnetic stirrer, and the water phase was used as the test medium following separation. Thus, the values for oil toxicity are calculated on the amount of oil added to IIL, water rather than the concentration of oil in the water column. 0 1 2 3 4 5 6 0 1 2 3 4 5 6 Using this procedure, a 24-hour median tolerance limit (TLm24) of NAPHTHENIC RINGS NAPHTHENIC RINGS white shrimp (Penaeus schmitti) for South Tia Juana medium crude was 15,000 ppm. For lisa (Mugil curema) the value was 2,400 Figure 6. Saturate compound-type distribution in Lake Maracaibo (figure 7). Robalo (Centropomus ensiferus) was about 10 times sediment dredge samples (numbers on map refer to station numbers)

EXP65 f / 37.2% of the saturate hydrocarbons were found to be paraffinic H20 ' .a. 1/ / compounds. None of the three dredge samples containing bitumi- / X 0 ppm nous particles (stations 2, 12, and 31) showed a predominance of A 1667 ppm paraffins. • 3333 ppm The relative deficiency of paraffinic hydrocarbons in the saturate O 6666 ppm fractions of most of the sediment samples examined results from -if / ■ 13.333 ppm selective microbial oxidation of these compound types. Saturate hydrocarbons are attacked by more microbial species, and more rapidly, than either naphthenic or aromatic compounds [14]. This : tl i being the case, a direct comparison of the saturate patterns of crude t J; -r-r-i-rrrr oil residues with those of the sediment organic extracts would 100 1000 provide little evidence for or against the presence of petroleum TIME, MINUTES bitumen in the sediments. A more productive approach might be one in which the saturate patterns of sediments known to contain bitumen are compared with those from other sediments. Qualita- tively, it would appear that over one-half of the samples have saturate patterns similar to the sample taken near Lagunillas (station 2) or Ule (station 13); i.e., a predominance of 2- and 3-ring naph- thenes. The results of distance correlation studies, and the mass spec- trometric analyses of saturate and aromatic fractions of sediment organic extracts, indicate that bituminous material is present in the sediments of most regions in the lake. The results further suggest that on the average, there is more bitumen present in sediments from the oil-producing areas than in those from other areas. Consid- ering the long history of intensive oil production in Lake Maracaibo, this trend is not particularly surprising. In addition to residue de- 1000 2000 3000 'C00 5000 6000 7000 riving from oil discharges, bituminous residues in sediments arise PARTS PER MILLION OF OIL ADDED from the numerous natural seeps that are present in almost every region of the lake. Due to the rapid rate of sedimentation in the lake Figure 7. (a) Mortality rates of lisa, Mugil curema, in concentrations system and the generally anoxic conditions of the lake bottom, it of 0 to 13,333 ppm of South Tia Juana medium crude oil. (b) would appear that the sediments probably represent a relatively Relationship between percent mortality (24 hours) and South Tia permanent repository for the insoluble nonvolatile portions of Juana medium crude oil concentration in water for lisa, Mugil petroleum discharged into the lake waters. curema. TLm24 is equal to 2,400 ppm. EFFECTS 495 more resistant than white shrimp to the toxic effects of South Tia Juana medium. The TLm values determined indicate the relative 100 sensitivity of the organisms. Under the same experimental conditions for each of the oil-water mixtures, there was a good correlation between mortality and the total crude oil added to the system. A dehydration chemical commonly employed in the processing of 80 the crude oil did not increase the toxicty of oil, but apparently decreased the induction time for the toxic response. V 24-HOUR MORTALITY Observations indicated that most of the mortality took place in N 60 the first 2 hours of exposure, in the experimental system, with little mortality thereafter, suggesting that the toxic components, primar- ily the low-boiling aromatics, were rapidly removed through aeration. Studies indicated that there was a marked reduction in K 40 2i= toxicity when organisms were exposed to the test medium following periods of aeration and exposure to sunlight. Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 In order to examine how these factors may influence the toxicity of surface films of oil on water, a series of experiments were 20 conducted in open tanks with oil without agitation. Samples of oil were extracted following "weathering," and organisms were exposed in the hypophase. The data showed that the mortality was significantly reduced by weathering. Oil spilled on the surface of Lake Maracaibo might possibly lose about one-half of its toxicity in less 0 120 240 360 than 1 hour. Analyses of the test medium showed that the concentration of monocyclic aromatics also diminishes with the time of WEATHERING TIME, MINUTES exposure of the oil film (figure 8). Figure 9 indicates the relationship between mortality, weathering time, and light aromatic concen- Figure 9. Relationship of weathering and concentration of light aro- tration in the water. Further investigations of the effect of the loss matics to shrimp mortality (same experiment as in figure 8) of the light aromatic fraction on mortality were conducted with Table 1. Hydrocarbon analysis of lisa exposed to daily spills of oil shrimp. These organisms were found to have a TLm24 of 1.36 ppm (0.65-2.9 ppm), total light aromatic fraction expressed at time zero, MllHHters of 011 Saturate Hydrocarbons Aromatic Hydrocarbons Total as compared with a TLm24 of 0.54 ppm (0.38-0.78), total light Spilled per Day Found (yg/g) ftfuhd (ug/g) (pg/g) aromatic fraction at 2 hours. 69.1 31.3 100.4

20 75.4 33.1 108.5 MINUTES AGING A 0 control 94.6 37.0 131.6 O 120 V 240 Table 2. Crude oil toxicity studies. Correlation of oil content D 480 • CONTROL variables with 24-hour mortality (values given are correlation -A coefficients).

Correlation of Quantity Correlation of Total Correlation of the Concentration x / 3.62 ppm Experiment of 011 Extracted 011 Concentration of Total Monoaromatlcs (GC) A AROMATICS Number with Mortality (IR) with Mortality with Mortality ~d?u 44 .963 .920 .805 49 .816 .356 .823 A O. ,o-°- 0.98 ppm ^J?V fo \ AROMATICS*^ ^ 50 .956 -.80 .810

^ 2.36 ppm ,V D' 53 .156 .963 .945 V AROMATICS <" J& 55 .387 -.394 .897 S?& rCP ^—-.0.61 ppm 57 .990 .364 .968 „^8 rQ AROMATICS 62 .927 .723 .913 D( ■ ***rrf\ ■ Q< ?«,+,I , , , i 63 .884 -.217 .869 10 100 1000 10.000

MINUTLS TO DtrtTH Table 3. Weathering studies. Correlation of oil content variables with 24-hour mortality (values given are correlation coefficients). Figure 8. Mortality of P. schmitti in aged water. Data shown for Correlation of Quantity Correlation of Total Correlation of the Concentration aromatics refers to initial concentrations of monocyclic aromatics Experiment of 011 Extracted 011 Concentration of Total Monoaromatlcs (GC) Number with Mortality (IR) with Mortality with Mortality found in toxicity test water. 46 -.915 .008 .804 To determine the effect on growth and the accumulation of hydro- 48 -.961 .143 .953 carbons, populations of lisa were subjected to daily exposures of oil 54 -.450 -.607 .868 in a flow-through system. Selected samples of water were analyzed for monocyclic aromatics in the initial period and low concentrations were observed. The fish were counted and weighed weekly. The correlation coefficients were determined between acute Mortality was insignificant over the 11 weeks. Average weight per toxicity of test medium and the physical/chemical parameters of the exposure was determined with no evidence for a significant differ- experiments. The data in table 2 show the correlation between the ence in the growth rates. The fish were analyzed at the termination quantity of crude oil extracted, oil in test medium by IR analysis, of the experiment. The data (table 1) indicate no significant differ- and total monocyclic aromatics of the test medium with mortality ence between the hydrocarbon content of the fish exposed to oil results. The data of table 3 gives the correlations with mortality for and the control fish. the weathering time, oil by IR, and aromatics. The results of the correlation of mortality with the oil concen- The correlation coefficients given in the tables are measures of tration of laboratory experiments may permit assessment of the the repeatability of the experimental results; thus, a coefficient of toxic potential of the hydrocarbon concentrations in the Lake unity indicates the experiments are repeated, the relationship Maracaibo ecosystem. Chemical analytical data for selected bioassay between two variables will always be the same. The closer to unity experiments were subjected to statistical correlation tests (tables 2 then, the more "perfect" the relationship between experimental and 3). variable and experimental results. 496 CONFERENCE ON PREVENTION AND CONTROL OF OIL POLLUTION

A general observation of the results in tables 2 and 3 is that the the degradation of the water quality which, consequently, may total oil concentration in the bioassay test media as measured by reduce the biological resources of the lake. infrared spectrophotometry is poorly related to toxicity. In 4 of the 11 tests studied the correlation is negative, while in only 2 tests the REFERENCES total oil content was positively correlated at the 95% level of confidence. Since gravimetric studies have shown that IR is a good 1. Redfield, A.C.; Ketchem, B.H.; and Bumpus, D.F. 1955. The indicator of oil concentration, the total oil content of lake water is hydrography of Lake Maracaibo, Ref. 55-9. Unpublished poorly related to the 24-hour mortality induced. report. Available from Creole Petroleum Corporation, In contrast, the total monocyclic aromatics concentration in the Caracas, Venezuela. test media appears to be consistently related to mortality. In each of 2. Gesener, F. von. 1956. Das plankton des Lago Maracaibo. In the 22 experiments studied, the correlation of aromatics with Ergebnisse der Deutschen Limnologischen Venezuela Espedi- induced mortality has a coefficient of 0.8 or greater. Five out of 22 tion, 1952, eds. F. von Gessner and Vereschi. Vol. 1, pp. experiments are correlated at the 95% confidence level. The total 67-92. aromatics concentration also appears to be a good indicator of tox- 3. Redfield, A.C. and Doe, L.A.E. 1964. Lake Maracaibo. Interna- icant concentration. For the experiments listed in table 2, the aro- tional Verein. Limnol 15:100-111. Downloaded from http://meridian.allenpress.com/iosc/article-pdf/1975/1/489/1738795/2169-3358-1975-1-489.pdf by guest on 29 September 2021 matics correlated strongly with quantity of oil extracted with only 4. Comision Coordinadore de los Programas de Estudio, Conser- two exceptions: experiments 53 and 55. The failure of oil extracted vacion y Aprovechamiento Integral, de la Cuenca Hidrologica to correlate with aromatiics concentrations in these experiments del Lago de Maracaibo. 1973. Informe de los Programas de tends to verify this analysis as a means of indicating the amount of Estudio, Conservacion y Aprovechamiento Integral, del Lago toxicant present, since the aromatics analyses relate very well to de Maracaibo. Presented at IX Congreso Venezulano de mortality for these two tests. Ingenieria, May 1974. The relationships among weathering time, analytical data, and 5. Pritchard, O.W., and Burt, W.V. 1951. An inexpensive and rapid mortality are particularly interesting (table 3). There was no correla- method for obtaining current profiles in estuarine waters. tion between total oil concentration and toxicity. However, there Chesapeake Bay Institute, John Hopkins University, Technical was a correlation between total aromatics and mortality. When Report No. 1 (unpublished manuscript). coupled with the observation that the aromatics concentration 6. Nemoto, T. 1971. La Pesca en El Lago de Maracaibo. Informe decreases significantly as weathering time continues, the data sug- Technico No. 24. Proyecto de Investigacion y Desarrollo gest that the "light ends," as represented in part by monocyclic Pesquaro (MAC-PNUD-FAO). Oficina Nacional de Pesca, aromatics, are significant contributors to toxicity of bioassay test Ministerio de Agricultura y Cria. Venezuela. media. The fairly rapid loss of these volatiles when exposed to 7. Griffiths, R.C., and Simpson, J.G. 1972. An evaluation of the "weathering" indicates that once spilled on water, these oils lose present levels of exploitation of the fishery resources of their potential for imparting acute toxicity to biota. This is due to Venezuela. Series Recusos y Explotacion Pesqueros. Vol. 2, volatilization of light components within a relatively short time. No. 5. Oficina Nacional de Pesca, Ministerio de Agricultura y Although the relationship between monocyclic aromatics and Cria. Venezuela. 24-hour mortality appears to be firmly established, the analytical 8. Templeton, W.L., ed. 1974. Study of effects of oil discharges results represent only a partial determination of the total hydrocar- and domestic and industrial wastewaters on the fisheries of bon contents of bioassay water. Other unidentified oil components, Lake Maracaibo. Vol. I. Ecological Characterization and such as saturates and rnercaptans, may also have substantial in- Domestic and Industrial Wastes. Battelle-Northwest, fluence on toxic response;. Thus, until more detailed information is Richland, Washington. available concerning the composition of lake extractions of crude 9. Templeton, W.L., ed. 1974. Study of effects of oil discharges oils, the data on aromatics are best considered as an indicator of and domestic and industrial wastewaters on the fisheries of total toxicant concentrations. Lake Maracaibo. Vol. II. Fate and Effects of Oil. Battelle- Northwest, Richland, Washington. CONCLUSIONS 10. Blumer, M. 1970. Dissolved organic compounds in sea water. Saturated and olefinic hydrocarbons and singly branched There is no question that significant discharges of oil and oil fatty Acids. In Organic Matter in Natural Waters, ed. D.W. compounds incidental to the production of petroleum in the Lake Hood. Institute of Marine Science Occasional Publication No. Maracaibo Basin have occurred over the last 4 decades in addition to 1, University of Alaska, June 1970:153. that material from natural seeps. However, the data obtained during 11. Brown, R.A.; Elliott, J.J.; and Searle, T.D. 1974. Measurement the course of this program from both laboratory and field studies and characterization of nonvolatile hydrocarbons in ocean would indicate that present operations have not caused discernible water. Proceedings, Marine Pollution Monitoring (Petroleum) damage. The rapid loss, in a few hours, of light hydrocarbons from Symposium and Workshop, May 13-17, 1974. Gaithersburg, surface films of oil to the atmosphere has been shown to reduce the Md.: National Bureau of Standards (in press). toxicity to organisms significantly. The low concentrations of oil 12. Blaylock, J.W.; O'Keefe, P.W.; Roehm, J.N.;and Wildung, R.E. measured in lake water have not contributed to a detectable buildup 1973. Determination of n-alkane and methylnaphthalene of hydrocarbons in the muscle tissue of selected commercial species. compounds in shellfish. Proceedings of Joint Conference on The occurrence of bitum inous residues in the sediments, particularly Prevention and Control of Oil Spills, March 13-15, 1973, p. in the production areas, would suggest that the natural processes of 173. Washington, D.C.: American Petroleum Institute. volatilization, biodegradation, and sedimentation are the major 13. Zo Bell, C.E. 1969. Microbial modification of crude oil in the mechanisms for removing weathered oil from the biologically pro- sea. Proceedings of Joint Conference on Prevention and Con- ductive zone. Examination of the limited fisheries data available does trol of Oil Spills, Dec. 1969, p. 317. Washington, D.C.: Amer- not suggest that the resources are being depleted. Consideration of ican Petroleum Institute. the potential impact of nonpetroleum wastes, both domestic and 14. Dixon, W.J., and Massey, F.J., Jr. 1951. An introduction to industrial, indicates that nonpetroleum materials are contributing to statistical analysis. New York: McGraw-Hill.