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The distribution and behaviour of tar balls along the Israeli coast
Estuarine,
Coastal and Sherf Science (1982) 15, 267-276
The Distribution and Behaviour of Tar Balls Along the Israeli Coast
Abraham Israel National Haifa, Israel
Golik Oceanographic
Institute,
P.O. Box 8030,
Received 15 July 1981
Keywords: tar; oil pollution;
coasts; Israel coast
A fortnightly sampling of tar balls on six beaches along the Israeli coastline between 14 April 1975 and 25 June 1976 showed that the mean content of tar during that period was 3625 g m-i of beach front. The northern and central parts of the coast were significantly more polluted than the southern part. Between July 1975 and February 1976 the mean tar quantity decreased continuously from 5635 to 1344 g m-l. A comparison of tar quantities on the Israeli beaches with those of other beaches in the world showed that the Israeli beaches are more polluted than those of the west Atlantic coast, are as polluted as other beaches on the eastern coast of the Mediterranean Sea, and are less polluted than the beaches of Alexandria, Egypt, and Paphos, Cyprus. It is suggested that the tar content on the beach is related to the degree of oil pollution in the sea. The closer a beach is to an oil shipping lane or an oil dumping site, the heavier it is polluted. During storms, beach tar balls are pushed by the waves to the back of the beach or, in the case of a cliffed coast, are carried along the shore by the longshore current. When the tar balls reach a gap in the cliff (such as an estuary), they are carried inland by the storm waves. There the tar may become buried or dry, shrink and break into small particles which are then dispersed by the wind.
Introduction Tar
ball pollution
on beaches results from discharge
of oil compounds into the sea as bilgewaste from land (Butler eb al., 1973; Nelson-Smith, 1973) and in some cases from oil seepages from the sea bottom (Landes, 1973). As the light fractions of these oil compounds evaporate, the oil viscosity increases
water from vessels,sludgefrom oil tankers, industrial
until tar balls are formed. The tar balls are carried by winds, currents and waves until they are beached. Tar pollution on beacheshasbeen a global phenomenonfor severaldecades.Nevertheless, very little systematicwork hasbeendone on this problem. Most of the researchhasbeendone on the western
beaches of the Atlantic
Ocean. Dennis
(1959) monitored
tar accumulation
on
Golden Beach, Florida; this was repeated, at the samebeach, 13 years later by Curtis & Saner (1974). Butler et al. (1973) studied tar content in Bermuda, and Ray et al. (1974) measuredtar content on the beach at Galveston, Texas. Additional reports on observations of tar pollution on beachesinclude those of Dwivedi & Parulekar (1974) from India and Okera (1974) from Sierra Leone. 267 0272-7714/82/090267
+ I I
803.00/o
@ 1982 Academic Press Inc. (London)
Limited
268
A. Golik
In 1976 a multinational project, designed to study the pollution of the Mediterranean Sea, was launched by the United Nations Environment Programme (UNEP). This project includes, among others, a study of beach pollution by tar balls. Preliminary results were recently issued (UNEP, 1980) including reports of tar ball pollution on the beaches of Cyprus, Egypt, Israel, Lebanon, Malta, Turkey and Yugoslavia. The purpose of this study was to estimate the quantity of tar on the Mediterranean beaches of Israel and to serve as a reference study to which future, similar studies may be compared.
Methods Sampling design It is of great importance, if possible, to measure the rate at which tar lands on the beach from the sea. However, when an experiment is designed to measure this parameter, it is important to realize that waves cause lateral movement of tar balls along the beach. Therefore, a repeated sampling of a narrow beach strip yields the rate of tar accumulation from both the sea and the beach on either side of the sampling strip. In order to evaluate the importance of the lateral movement of tar, on 22 May 1975 painted tar balls were spread along a line perpendicular to the shoreline of the beach at Atlit. Five days later painted tar balls were found as far as 43 m away from their original position. During these five days, the sea was calm and only those tar balls close to the waterline were moved. Longshore movement of tar balls is, therefore, significant and, depending on the wave conditions, may be scores or even hundreds of meters per day. There are many reports in the literature in which tar accumulation rates are given in units of weight per meter per time. One should be aware that these accumulation rates may be a mixture of onshore and lateral movement of tar balls. In order to measure the true rate of accumulation of tar washed up onto a beach, it is necessary to clean thoroughly a long section of the beach (W IOO m) from tar and then to collect daily the tar balls which accumulate on a narrow strip at the center of that section. Even then, in stormy days, lateral movement will distort the results. Such an experiment is very costly and laborious and could not be carried out in the present study. Therefore, the aim of this study was restricted to measuring the standing crop of tar on the beach, rather than the more desirable rate of accumulation. Accordingly, a new r-m strip of beach was used for sampling each time. Field and laboratory work Six sandy beaches affected by only minor human and vehicular activity were selected for sampling purposes (Figure I). Sampling was carried out between 14 April 1975 and 25 June 1976 at about fortnightly intervals except for El Arish beach, which was sampled only once a month. A total of 225 samples were collected for this study. A sample consisted of the tar balls which were collected from a strip of beach, I m wide, oriented perpendicular to the shoreline from the water line to the foot of the cliff or dune, with length ranging from 5 to 45 m. Two samples, several meters to several scores of meters apart, were taken each time from every beach. Each time a new strip was selected for sampling. Tar was collected by gently brushing the beach surface with a road brush. Piles of tar mixed with sand formed by brushing were put into a box, the walls and bottom of which were made of an iron net with 2 mm hole size. The box was carried to the sea where the water washed out the sand, leaving the tar balls in the box. These were put in bags and sent to the laboratory where the tar was spread on trays to dry. After removal of all foreign
Distribution
and behaviour of tar balls
269
material such aspebbles,wood, shellsetc., the tar wasweighed. The error in weight due to foreign material which was not removed is estimated at no more than ~0% of the sample weight. In addition, the burial processesof tar in the sandwere followed on the beachof Ashqelon between 23 October 1975 and 25 June 1976.A sampler, similar in shapeto a box corer, was used for this purpose. The sampler has two sidesand a back made of stainlesssteel held together by a frame, 20 x 20 cm on the sidesand IO cm high. On the sides,five metal guides are welded at 2 cm vertical spacing.These enablethe metal trays to slide into the samplerin
330
34* Figure
I. Sampling
location
map.
the sameway that drawers slide into a cabinet. In the field, the samplerwas pushed all the way into the sand. Then a shallow trench was dug in front of the sampler. The metal trays were then slid from the front into the sampler. When all five trays were in the sampler, it wastaken out of the sandand the trays carefully removed. Each tray contained a beach sand sampleof 20 x 20 x 2 cm. In the laboratory, the sandwassieved out, leaving the tar particles which were then weighed. This gave the distribution of tar content at z-cm intervals to a depth of IO cm. Sampleswere taken perpendicular to the shorelineat 5-m intervals from the foot of the cliff to the water line.
A. Golik
270
II
f
I
I
I,
I
I
I
I
I
I
I
I
4MJJ4SONDJFMAMJ I975
t976 Month
Mean tar quantity (f4 m-9 Range (g m-l)
Figure
z. Mean
tar ball distribution
TABLE
I. Mean
tar ball auantities
El Arish
Ashqelon
884 30-205.5
3014 391-11 I33
as a function
on six Israeli
Ga’ash
4186 254-12150
of time
of Israel.
beaches
Bet Yannay
4x14 375-14759
Rosh HaNiqra
Atlit
4388 678-13052
3902 481-13 502
foreshore
fomhora 28
for the beaches
33m
2 : 0 IO
26.1.76
23.10.75
9.2.76
22.12.75 3 2 4 6 8 IO
6 13 18 23 28m from the foot of the cliff
13. I .?6 41
l-3
3-77-1515-30~30 g (800 cmW
Figure depth
3, Tar distribution in Ashqelon below the beach surface.
as a function
of position
on the beach
and
Distribution
and behaviour of tar balls
271
Results Between 14 April 1975 and 25 June 1976the mean tar quantity found on the Israeli beaches was 3625 g m-l of beach front from the waterline to the foot of the cliff or dune with a standard deviation of 2834 and a range of 30-14 759 g. The distribution of tar quantity as a function of time is given in Figure 2, where it can be seenthat from spring 1975 to midwinter 1976 there was a decreasein the mean tar quantity from 6107 to 1344g m-l. This decreasefollows a regressionline with a correlation value Y = 0.509, having a significance value of 0.01. From mid-winter to spring 1976the tar quantity increasedto 4361 g m-l and from then on a decreaseis indicated. The geographicaldistribution of tar is given in Table I, where it can be seenthat the northern and central beachesare the most polluted oneswhereasthe southernmostbeach is the cleanest.A t-test revealed no significant difference between the tar quantities of Rosh HaNiqra, Atlit, Bet Yannay and Ga’ash, but there is a significant difference (0.05 level) between these beachesand Ashqelon and an even more significant difference (
Discussion Comparison
of tar quantity
on the Israeli beach with other beaches
A comparison of tar quantities on the Israeli beacheswith those reported in studies from other beachesin the world is rather difficult becauseof differencesin methodsemployed in various studies. Many workers who studied tar content on the beach were not aware of the differences between rate of tar accumulation and standing crop of tar. In many studies (UNEP, 1980) tar was collected from a narrow strip (I or 2 m of frontal beach) with a samplinginterval of IO-IS days. The results of studiessuch as theserepresentthe standing crop rather than the rate of accumulation. In other studies(Dennis, 1959; Curtis & Saner, 1974; Ray et al, 1974) relatively long sectionsof frontal beach were sampleddaily or once in 2 days. The results of thesestudiesare closerto the true rate of tar accumulation. Table 2 summarizesthe findings of tar content on various Mediterranean beaches(UNEP, 1980) and comparesthem with the results of this study. All these studies are basedon tar which was collected from narrow strips of beach at sampling intervals ranging between IO and 15 days. They therefore representa parameter which is very closeto the standing crop of tar, The results of our study were converted from units of g m-l to g m- 2 (IS days)-’ to permit comparison. The only difference between our study and the studies reported in UNEP (1980) is that in our study a new strip of beachwasselectedat eachsampling,whereas in the UNEP (1980) studies the samestrip was apparently used each time. This difference should causea slight bias towards higher values for the Israeli beach. Examination of Table 2 shows that the beachesof Paphos, Cyprus, and Alexandria, Egypt (seeFigure 4) are the most polluted ones. It is interesting to note that the beach of Limassol,Cyprus, is an order of magnitude lesspolluted than that of Paphos. In the same way, the beachesof Israel, Lebanon and Turkey are significantly lesspolluted than those of Paphos and Alexandria. A plausible explanation for this pattern may be found in the location in which it is legitimate to dispose of sludge and other oil compounds in the
A. Golik
T-LB
2. Tar
Country Malta Malta Cypl-US CYPrEiwt Lebanon Lebanon Turkey Israelb
quantities
on various
Beach
Period
Anchor Bay Marsaxlokk Bay Limassol Paphos Alexandria Ramlet Sidar Erdemli mean of six beaches
beaches
Sampling
of study
Apr 77-Sep Apr ‘n-Sep Nov 77-Nov Nov 77-Nov Apr @-May Apr 77-b Apr 77-Jun Icm-I978 Apr 75-Jun
“Values are reported as g rn-% day-l days -I) to permit comparison. *Reported in the present study.
$2; - -
Mediterranean
78 78 78 78 79 78 78 76 and
Tests
3. Tar
Beach Florida Florida Texas Bermda Israel “See comments
quantities
recalculated
Dennis Curtis W et Butler present
A 0
(wsg) & Saner (1974) aI. (1974) et aI. (1973) study
on the tar quantities
rate
Mean tar quantity 63 m-9
here
62.3” 6.3” 31’5 360.3 132.0 4’0 3’8 24’3 14.6 back
to g me2
6.1-12 w 1-l 124-2opg 1“
site for oil and sludge and concentrations found by Oren (personal communication)
on some beaches
Reference
x980)
every 15 days every 15 days every g days every g days every 15 days monthly monthly only 3 samplings every 15 days
Dump sih tar ail cornpods Oil traffic routes
Figure 4. Oil shipping lanes, dump dissolved petroleum hydrocarbons between 1977 and 197%
(UNEP,
in North
America
Quantity
of tar”
and in Israel
534gm-‘year-’ 2005 g m-i year-r 1606 g m-l year-’ Igo g m-l 3625 g m-l of this table
in the Discussion.
(I 5
30.
of
Distribution
and behaviour of tar balls
273
Mediterranean Sea (Figure 4). The beachesof Paphosand Alexandria are the closestto one of these disposalareasand therefore are greatly affected by it. The beach of Limassolis on the opposite side of Cyprus relative to the disposalarea and therefore suffers lessfrom tar pollution. Similarly, the beachesof Israel, Lebanon and Turkey are at a greater distance from the dump site than those of Cyprus and Egypt and are therefore lesspolluted. Table 3 gives the tar quantities reported from various beacheson the Atlantic side of North America and those found in Israel. In the studies of Dennis (1959), Curtis & Saner ar was sampled daily or once in 2 days from beach sections (1974) and Ray et d (r974), t ranging in frontal length from 6.6 to 48.6 m year round. The valuesgiven (g m-l year-l) are the sum of all the tar collections during a year adjusted to I m of beachfront. These values, therefore, closely represent the rate of tar accumulation. The study of Butler et al. (1973) and the presentstudy are basedon weekly and fortnightly sampling,respectively, of only I m of beachfront. The valuesin Table 3 for thesetwo studiesare the meantar quantity, and they represent the standing crop of tar. It is impossibleto make a direct and accurate comparison between the values given in Table 3 becausethey are not the sameparameter. However, if we make the assumptionthat it takes I year of tar accumulation until the tar reachesa steady-state condition (which is equivalent to standing crop), then the Israeli beachesare 1.8-68 times more polluted than those of Florida and Texas and 19 times more than those of Bermuda. Basedon field observations,the author is of the opinion that it takes lessthan a year for the tar quantity on the beach to get to a steady-state condition. Therefore, the above assumptionwould distort the comparison so that the tar quantity on the Israeli beaches would be smaller in that comparison. The conclusion is, therefore, that the Israeli beaches are much more polluted than the beacheslisted in Table 3. The large quantity of tar on Israeli beachesis undoubtedly due to the heavy pollution of the Mediterranean with oil. Horn et al. (1970) report on an averageof 20 mg mW2of pelagic tar on the surface of the Mediterranean with a maximum of 540mg mR2. According to Butler et al. (1973)~ this is the highest concentration of pelagic tar in the world, the global averagebeing 3 mg m- 2. Quantitative
distribution
of tar in space and time
The results of this study do not provide a clear explanation of the fluctuation of tar quantity in space and time. We can, however, examine some of the factors which influence tar distribution in light of our results. OiZ trufic. Figure 4 showsthe lanes of oil trafhc in the Mediterranean. During the first 2 months of this study, as well as 8 years before it started, the Suez Canal was closed. The quantity of oil shipped through the canal immediately after its opening wasvery small. The influence of this lane on the Israeli coast during our study must therefore have been very limited. The only oil trafhc lane that could causepollution to the southern part of the Israeli coastis the one connecting the terminal of the Elat-Ashqelon oil pipeline with Europe. The heavy transport of oil in the East Mediterranean is along the routes betweenthe oil terminals of Syria and Lebanon and Europe. This heavier oil traffic in the northern part of the eastern Mediterranean is reflected in the heavier pollution of tar balls on the central and northern beachesof Israel. Distribution of tar balls in the sea.Oren (personalcommunication, 1970)collected tar during four cruises in the eastern Mediterranean in 1970 and 1971. He reported his findings in
274
A. Golik
relative rather than absolute terms. In all these cruises, high concentrations of tar balls were found between Cyprus and the Lebanese coastline. Oren (1970) relates these concentrations to the geostrophic currents which prevail in this area. They form a gyre with a no-motion area between Cyprus and Lebanon, and in this no-motion area the tar is concentrated. During storms, this area feeds the Syrian, Lebanese and northern Israeli coasts with tar. Distribution of dissolved and dispersed petroleum hydrocarbons in the sea. High concentrations of dissolved and dispersed petroleum hydrocarbons in the sea should indicate loci of oil spillage9 and hence loci of tar ball origin. Between 1977 and 1979, Oren & Ravid (in preparation) conducted six cruises to the eastern Mediterranean during which dissolved oil compounds were measured. High concentrations were found in two areas: between Cyprus and the Israeli-Lebanese coastline and west of Cyprus (Figure 4). The first location is identical to the area in which a high concentration of tar balls was found, and the other is in the area where discharge of oil into the sea is permitted. Sources of tar. Shekel & Ravid (1977) studied the sources of tar balls on the Israeli beaches based on the chemical composition of the tar balls. These workers analysed 788 tar balls which were collected fortnightly between 1973 and 1975 from eight stations along the Israeli beach. It was found that 76% of the tar balls were formed from crude oil and crude oil sludge, and 22% from fuel oil. Furthermore, on the basis of the nickel : vanadium ratio and sulfur content of the tar balls, it was found that practically all of the tar (96%) was formed from oil of the Persian Gulf or from the Gulf of Suez. No tar balls with the chemical composition characteristic of Libyan oil were found. The distribution of tar balls and dissolved oil compounds in the sea, the routes of oil transport in the eastern Mediterranean, and the origin of the tar balls which pollute the Israeli coastline indicate that the source for most of the tar pollution is between Cyprus and the Israeli-Lebanese coast. It is harder to explain the fluctuation of tar concentration as a function of time. The continuous decrease in tar quantity from 5635 g m-l in July 1975 to 1344 g m-1 in February 1976 could be a result of an event occurring at that time (reduction on oil shipment I, enforcement of regulations against oil spillages 7) which caused this decrease. Alternatively, this may be a phenomenon which repeats itself every year, causing cycles in tar quantity. A longer period of sampling is required to find whether such a cycle indeed exists. Tar behaviour and fate on the beach On the basis of data collected and observations made during this study, the processes which control tar ball distribution on the beach may be described as follows. Tar balls are formed by the evaporation of the light fractions of oil compounds which were spilled into the sea. The floating tar balls are driven by the winds, waves and currents onshore. Once landed on the beach, sand grains, shells and beach pebbles are attached to the tar ball, increasing its specific gravity. Therefore, tar balls which land on the beach can no longer float and may be found either in the water column or on the bottom. The hydrodynamic characteristics of the tar balls are such that the waves force them back to the shore. Searches for tar balls on the sea bottom beyond the breaker zone were conducted several times by divers and only very rarely was a tar ball found on the sea bottom. It may therefore be concluded that the eventual fate of the tar balls is to land and remain on the beach. Once on the beach, tar balls concentrate along the swash marks and move landward with the rising tide. Each successive higher tide, wave or storm causes a further landward move-
Distribution
and behaviour of tar balls
275
ment of the tar towardsthe backshore.The result is the concentration of tar on the backshore asseenin Figure 3. Occasionally, tar may be found on or near the waterline, indicating that its landing occurred just a short time previously. In the courseof this study, a large concentration of tar balls wasfound on the waterline on 12 May 1976.Thesetar ballswere very soft, uniform in shapeand size and created a continuous line of tar balls more than 50 km long north of Tel-Aviv. This undoubtedly resulted from an event of tar pollution by a ship or oil tanker that spilled its bilge water or oil sludgewhile passingalong the coast a few hours earlier. Indeed, chemical analysesof this tar showedthat it still contained paraffins down to C,, which normally evaporate within a day after spillage. On the next day, the sametar was still distinguishableas a continuous line of tar balls. It had, however, already moved several meters landward, was partly covered with sand, and had started to be incorporated into the rest of the tar population. On the beach, in the foreshore zone, the tar cannot be buried becauseeach time a wave runs up the beach it stirs up the beach material. The tar, being lighter than the sand, settles after the sandand remainson the beachsurface. Beyond the foreshore,the tar may be buried by the sandwhich is blown on the beach. The burial is to a depth of 50-70 cm but not for an extended period of time. During the winter, when storms occur, the author observed the waves swashthe whole beach and reach the foot of the cliff. These waves unearthed the buried tar and moved it both in an on-offshore direction and in a longshoredirection. The tar ballsmove along the shoreuntil they reach a point where there is no coastal cliff, such asa river valley or estuary. There, the wavesmay penetrateinland to a distanceof 200-300 m from the beach, carrying the tar with them. The seawaterwhich carries the tar to that distancelandward percolatesinto the sand on its way to the seaand there is no mechanism to carry the tar back to the beach. River valleys or other topographical depressionsin the backshoreserve asfinal traps for the tar [Plate r(a) (b)]. In order to get someideaabout the final fate of the tar, a fresh tar ball wasplacedon a cliff ledge so that waves could not reach and remove it. During the seven months that the ball stayed there, a hard skin was created around it; then the ball shrunk and becamemore brittle with increasing fissures all over it. Finally it started to disintegrate into 2-3 mm fragments that were shred off the ball and dispersedby the wind.
Summary
and conclusions
Measurements of tar quantities along the Israeli coastlineshowedthat between April 1975 and June 1976the averagetar content on the beachwas 3625 (S.D. = 2834)g m-l of frontal beach. This may serve as a referencevalue for comparisonwith future studies.Examination of tar data from various beachesin the easternMediterranean suggeststhe influence of an oil and sludgedump site in the seawest of Cyprus. Tar content on beachescloseto that dump site, such as Alexandria, Egypt, or Paphos, Cyprus, is an order of magnitude higher than that of beachesalong the easternshoresof the Mediterranean Sea. Comparisonbetweenthe Israeli beachesand somebeachesin North America showsthat the former are more polluted. This is not surprising in view of the heavy oil trafhc in the Mediterranean (23o/oof the world trafhc in 1975 according to Le Lourd, 1977) which causesthis seato be the most oil polluted in the world (Butler et al, 1973; Osterberg & Keckes, 1977). Comparisonof tar quantities amongthe various beachesof Israel showsthat the northern and central coastsof Israel are more polluted than the southern coast. This appearsto be due to a combination of oil shipping lanes and oceanographicconditions which causehigh concentrations of dissolved oil and tar lumps between Cyprus and Israel and Lebanon. A continuous decreasein tar
Cb)
Plate I. T ar accumulation on Bet Yannay beach following a winter storm. (a) on a cliffed beach. (b) Further along the beach from (a) where no cliff exists. Notice lack of tar in (a) and abundance of tar balls in (b).
A. Golik
276
quantity was found between July 1975 and February 1976, but no explanation for this can be offered at present. After landing on the beach, the tar balls are pushed to the back of the beach by each successive wave, tide or storm. During severe storms, it was noticed that tar balls are carried by longshore currents along the beach until they reach a low-lying land at the back of the beach. There, during storms, the waves may carry the tar balls zoo-300 m inland and there is no mechanism for their return. It is proposed that finally the tar is either buried by windblown sand or dries and mechanically disintegrates into small particles which are then dispersed by the wind. Acknowledgements Thanks are due to Y. Tandler and R. Holzer for their assistance in the field and laboratory work. A. Back, D. Bowman, V. Goldsmith, Y. Mart and A. Tandler critically read the manuscript and offered useful comments. This study was supported by the Israeli Environmental Protection Service. References Butler,
J. N.,
Morris,
B. F. & Sass, J.
Bermuda pp. Curtis, M. & Saner, A. 1974 Tar ball loadings on Golden Beach, Florida. Natiunal Bureau of Standards Special Publication No. 409. pp. 79-81. Dennis, J. V. 1959 Oil pollution survey of the U.S. Atlantic coast. 1973
Pelagic
tar from
Biological Slation Research Special Publication No.
and Sargasso
Sea.
Bewcuda
IO. 346
U.S. Departmezt of C%nmerce, American Petroleum Institute
Publication No. 4054. Dwivedi,
S. N. & Parulekar,
A. N. 1974
Oil pollution
Commerce, National Bureau of Stanabds Horn,
M.
H., Teal,
J. M. & Backus,
R. H. 1970
along
coastline. U.S. Department of pp. IOI-105. on the surface of the sea. Science 168,
the Indian
Special Publication No. Petroleum
lumps
409.
245-246.
Landes,
K. K.
1973
Mother
Bulletin 57,637-64x.
nature
as an oil polluter.
American Association of Petroleum Geologists
Le Lourd, P. 1977 Oil pollution in the Mediterranean Sea. Am& 6,3X7-320. Nelson-Smith, A. 1973 OiI Pollution and Marine Ecology. Plenum Press, New York. 260 pp. Okera, W. 1974 Tar pollution of Sierra Leone beaches. Nature 252,682. Oren, 0. H. 1970 Tar pollution of the Levant Basin. Marine Pollution Bulletin I, 149-ISO. Osterberg, C. & Keckes, S. 1977 The state of pollution of the Mediterranean Sea. An&o 6, 321-326. Ray, S. M., Oja, R. K., Jeffrey, L. M. & Presley, B. J. 1974 A quantitative and qualitative survey of oils and tars stranded on Galveston Island beaches. Department of Transportation, U.S. Coast Guard Report No. CG-D-10-75. Shekel, Y. & Ravid, R. 1977 Sourcea of tar pollution on Israeli Mediterranean coast. Environmental Science and Technology II, 502-505. United Nations Environment Programme 1980 Summary reports on the scientific results of MED POL, Part I. UNEP/IG II/INF 3. 202 pp.
Coastal and Sherf Science (1982) 15, 267-276
The Distribution and Behaviour of Tar Balls Along the Israeli Coast
Abraham Israel National Haifa, Israel
Golik Oceanographic
Institute,
P.O. Box 8030,
Received 15 July 1981
Keywords: tar; oil pollution;
coasts; Israel coast
A fortnightly sampling of tar balls on six beaches along the Israeli coastline between 14 April 1975 and 25 June 1976 showed that the mean content of tar during that period was 3625 g m-i of beach front. The northern and central parts of the coast were significantly more polluted than the southern part. Between July 1975 and February 1976 the mean tar quantity decreased continuously from 5635 to 1344 g m-l. A comparison of tar quantities on the Israeli beaches with those of other beaches in the world showed that the Israeli beaches are more polluted than those of the west Atlantic coast, are as polluted as other beaches on the eastern coast of the Mediterranean Sea, and are less polluted than the beaches of Alexandria, Egypt, and Paphos, Cyprus. It is suggested that the tar content on the beach is related to the degree of oil pollution in the sea. The closer a beach is to an oil shipping lane or an oil dumping site, the heavier it is polluted. During storms, beach tar balls are pushed by the waves to the back of the beach or, in the case of a cliffed coast, are carried along the shore by the longshore current. When the tar balls reach a gap in the cliff (such as an estuary), they are carried inland by the storm waves. There the tar may become buried or dry, shrink and break into small particles which are then dispersed by the wind.
Introduction Tar
ball pollution
on beaches results from discharge
of oil compounds into the sea as bilgewaste from land (Butler eb al., 1973; Nelson-Smith, 1973) and in some cases from oil seepages from the sea bottom (Landes, 1973). As the light fractions of these oil compounds evaporate, the oil viscosity increases
water from vessels,sludgefrom oil tankers, industrial
until tar balls are formed. The tar balls are carried by winds, currents and waves until they are beached. Tar pollution on beacheshasbeen a global phenomenonfor severaldecades.Nevertheless, very little systematicwork hasbeendone on this problem. Most of the researchhasbeendone on the western
beaches of the Atlantic
Ocean. Dennis
(1959) monitored
tar accumulation
on
Golden Beach, Florida; this was repeated, at the samebeach, 13 years later by Curtis & Saner (1974). Butler et al. (1973) studied tar content in Bermuda, and Ray et al. (1974) measuredtar content on the beach at Galveston, Texas. Additional reports on observations of tar pollution on beachesinclude those of Dwivedi & Parulekar (1974) from India and Okera (1974) from Sierra Leone. 267 0272-7714/82/090267
+ I I
803.00/o
@ 1982 Academic Press Inc. (London)
Limited
268
A. Golik
In 1976 a multinational project, designed to study the pollution of the Mediterranean Sea, was launched by the United Nations Environment Programme (UNEP). This project includes, among others, a study of beach pollution by tar balls. Preliminary results were recently issued (UNEP, 1980) including reports of tar ball pollution on the beaches of Cyprus, Egypt, Israel, Lebanon, Malta, Turkey and Yugoslavia. The purpose of this study was to estimate the quantity of tar on the Mediterranean beaches of Israel and to serve as a reference study to which future, similar studies may be compared.
Methods Sampling design It is of great importance, if possible, to measure the rate at which tar lands on the beach from the sea. However, when an experiment is designed to measure this parameter, it is important to realize that waves cause lateral movement of tar balls along the beach. Therefore, a repeated sampling of a narrow beach strip yields the rate of tar accumulation from both the sea and the beach on either side of the sampling strip. In order to evaluate the importance of the lateral movement of tar, on 22 May 1975 painted tar balls were spread along a line perpendicular to the shoreline of the beach at Atlit. Five days later painted tar balls were found as far as 43 m away from their original position. During these five days, the sea was calm and only those tar balls close to the waterline were moved. Longshore movement of tar balls is, therefore, significant and, depending on the wave conditions, may be scores or even hundreds of meters per day. There are many reports in the literature in which tar accumulation rates are given in units of weight per meter per time. One should be aware that these accumulation rates may be a mixture of onshore and lateral movement of tar balls. In order to measure the true rate of accumulation of tar washed up onto a beach, it is necessary to clean thoroughly a long section of the beach (W IOO m) from tar and then to collect daily the tar balls which accumulate on a narrow strip at the center of that section. Even then, in stormy days, lateral movement will distort the results. Such an experiment is very costly and laborious and could not be carried out in the present study. Therefore, the aim of this study was restricted to measuring the standing crop of tar on the beach, rather than the more desirable rate of accumulation. Accordingly, a new r-m strip of beach was used for sampling each time. Field and laboratory work Six sandy beaches affected by only minor human and vehicular activity were selected for sampling purposes (Figure I). Sampling was carried out between 14 April 1975 and 25 June 1976 at about fortnightly intervals except for El Arish beach, which was sampled only once a month. A total of 225 samples were collected for this study. A sample consisted of the tar balls which were collected from a strip of beach, I m wide, oriented perpendicular to the shoreline from the water line to the foot of the cliff or dune, with length ranging from 5 to 45 m. Two samples, several meters to several scores of meters apart, were taken each time from every beach. Each time a new strip was selected for sampling. Tar was collected by gently brushing the beach surface with a road brush. Piles of tar mixed with sand formed by brushing were put into a box, the walls and bottom of which were made of an iron net with 2 mm hole size. The box was carried to the sea where the water washed out the sand, leaving the tar balls in the box. These were put in bags and sent to the laboratory where the tar was spread on trays to dry. After removal of all foreign
Distribution
and behaviour of tar balls
269
material such aspebbles,wood, shellsetc., the tar wasweighed. The error in weight due to foreign material which was not removed is estimated at no more than ~0% of the sample weight. In addition, the burial processesof tar in the sandwere followed on the beachof Ashqelon between 23 October 1975 and 25 June 1976.A sampler, similar in shapeto a box corer, was used for this purpose. The sampler has two sidesand a back made of stainlesssteel held together by a frame, 20 x 20 cm on the sidesand IO cm high. On the sides,five metal guides are welded at 2 cm vertical spacing.These enablethe metal trays to slide into the samplerin
330
34* Figure
I. Sampling
location
map.
the sameway that drawers slide into a cabinet. In the field, the samplerwas pushed all the way into the sand. Then a shallow trench was dug in front of the sampler. The metal trays were then slid from the front into the sampler. When all five trays were in the sampler, it wastaken out of the sandand the trays carefully removed. Each tray contained a beach sand sampleof 20 x 20 x 2 cm. In the laboratory, the sandwassieved out, leaving the tar particles which were then weighed. This gave the distribution of tar content at z-cm intervals to a depth of IO cm. Sampleswere taken perpendicular to the shorelineat 5-m intervals from the foot of the cliff to the water line.
A. Golik
270
II
f
I
I
I,
I
I
I
I
I
I
I
I
4MJJ4SONDJFMAMJ I975
t976 Month
Mean tar quantity (f4 m-9 Range (g m-l)
Figure
z. Mean
tar ball distribution
TABLE
I. Mean
tar ball auantities
El Arish
Ashqelon
884 30-205.5
3014 391-11 I33
as a function
on six Israeli
Ga’ash
4186 254-12150
of time
of Israel.
beaches
Bet Yannay
4x14 375-14759
Rosh HaNiqra
Atlit
4388 678-13052
3902 481-13 502
foreshore
fomhora 28
for the beaches
33m
2 : 0 IO
26.1.76
23.10.75
9.2.76
22.12.75 3 2 4 6 8 IO
6 13 18 23 28m from the foot of the cliff
13. I .?6 41
l-3
3-77-1515-30~30 g (800 cmW
Figure depth
3, Tar distribution in Ashqelon below the beach surface.
as a function
of position
on the beach
and
Distribution
and behaviour of tar balls
271
Results Between 14 April 1975 and 25 June 1976the mean tar quantity found on the Israeli beaches was 3625 g m-l of beach front from the waterline to the foot of the cliff or dune with a standard deviation of 2834 and a range of 30-14 759 g. The distribution of tar quantity as a function of time is given in Figure 2, where it can be seenthat from spring 1975 to midwinter 1976 there was a decreasein the mean tar quantity from 6107 to 1344g m-l. This decreasefollows a regressionline with a correlation value Y = 0.509, having a significance value of 0.01. From mid-winter to spring 1976the tar quantity increasedto 4361 g m-l and from then on a decreaseis indicated. The geographicaldistribution of tar is given in Table I, where it can be seenthat the northern and central beachesare the most polluted oneswhereasthe southernmostbeach is the cleanest.A t-test revealed no significant difference between the tar quantities of Rosh HaNiqra, Atlit, Bet Yannay and Ga’ash, but there is a significant difference (0.05 level) between these beachesand Ashqelon and an even more significant difference (
Discussion Comparison
of tar quantity
on the Israeli beach with other beaches
A comparison of tar quantities on the Israeli beacheswith those reported in studies from other beachesin the world is rather difficult becauseof differencesin methodsemployed in various studies. Many workers who studied tar content on the beach were not aware of the differences between rate of tar accumulation and standing crop of tar. In many studies (UNEP, 1980) tar was collected from a narrow strip (I or 2 m of frontal beach) with a samplinginterval of IO-IS days. The results of studiessuch as theserepresentthe standing crop rather than the rate of accumulation. In other studies(Dennis, 1959; Curtis & Saner, 1974; Ray et al, 1974) relatively long sectionsof frontal beach were sampleddaily or once in 2 days. The results of thesestudiesare closerto the true rate of tar accumulation. Table 2 summarizesthe findings of tar content on various Mediterranean beaches(UNEP, 1980) and comparesthem with the results of this study. All these studies are basedon tar which was collected from narrow strips of beach at sampling intervals ranging between IO and 15 days. They therefore representa parameter which is very closeto the standing crop of tar, The results of our study were converted from units of g m-l to g m- 2 (IS days)-’ to permit comparison. The only difference between our study and the studies reported in UNEP (1980) is that in our study a new strip of beachwasselectedat eachsampling,whereas in the UNEP (1980) studies the samestrip was apparently used each time. This difference should causea slight bias towards higher values for the Israeli beach. Examination of Table 2 shows that the beachesof Paphos, Cyprus, and Alexandria, Egypt (seeFigure 4) are the most polluted ones. It is interesting to note that the beach of Limassol,Cyprus, is an order of magnitude lesspolluted than that of Paphos. In the same way, the beachesof Israel, Lebanon and Turkey are significantly lesspolluted than those of Paphos and Alexandria. A plausible explanation for this pattern may be found in the location in which it is legitimate to dispose of sludge and other oil compounds in the
A. Golik
T-LB
2. Tar
Country Malta Malta Cypl-US CYPrEiwt Lebanon Lebanon Turkey Israelb
quantities
on various
Beach
Period
Anchor Bay Marsaxlokk Bay Limassol Paphos Alexandria Ramlet Sidar Erdemli mean of six beaches
beaches
Sampling
of study
Apr 77-Sep Apr ‘n-Sep Nov 77-Nov Nov 77-Nov Apr @-May Apr 77-b Apr 77-Jun Icm-I978 Apr 75-Jun
“Values are reported as g rn-% day-l days -I) to permit comparison. *Reported in the present study.
$2; - -
Mediterranean
78 78 78 78 79 78 78 76 and
Tests
3. Tar
Beach Florida Florida Texas Bermda Israel “See comments
quantities
recalculated
Dennis Curtis W et Butler present
A 0
(wsg) & Saner (1974) aI. (1974) et aI. (1973) study
on the tar quantities
rate
Mean tar quantity 63 m-9
here
62.3” 6.3” 31’5 360.3 132.0 4’0 3’8 24’3 14.6 back
to g me2
6.1-12 w 1-l 124-2opg 1“
site for oil and sludge and concentrations found by Oren (personal communication)
on some beaches
Reference
x980)
every 15 days every 15 days every g days every g days every 15 days monthly monthly only 3 samplings every 15 days
Dump sih tar ail cornpods Oil traffic routes
Figure 4. Oil shipping lanes, dump dissolved petroleum hydrocarbons between 1977 and 197%
(UNEP,
in North
America
Quantity
of tar”
and in Israel
534gm-‘year-’ 2005 g m-i year-r 1606 g m-l year-’ Igo g m-l 3625 g m-l of this table
in the Discussion.
(I 5
30.
of
Distribution
and behaviour of tar balls
273
Mediterranean Sea (Figure 4). The beachesof Paphosand Alexandria are the closestto one of these disposalareasand therefore are greatly affected by it. The beach of Limassolis on the opposite side of Cyprus relative to the disposalarea and therefore suffers lessfrom tar pollution. Similarly, the beachesof Israel, Lebanon and Turkey are at a greater distance from the dump site than those of Cyprus and Egypt and are therefore lesspolluted. Table 3 gives the tar quantities reported from various beacheson the Atlantic side of North America and those found in Israel. In the studies of Dennis (1959), Curtis & Saner ar was sampled daily or once in 2 days from beach sections (1974) and Ray et d (r974), t ranging in frontal length from 6.6 to 48.6 m year round. The valuesgiven (g m-l year-l) are the sum of all the tar collections during a year adjusted to I m of beachfront. These values, therefore, closely represent the rate of tar accumulation. The study of Butler et al. (1973) and the presentstudy are basedon weekly and fortnightly sampling,respectively, of only I m of beachfront. The valuesin Table 3 for thesetwo studiesare the meantar quantity, and they represent the standing crop of tar. It is impossibleto make a direct and accurate comparison between the values given in Table 3 becausethey are not the sameparameter. However, if we make the assumptionthat it takes I year of tar accumulation until the tar reachesa steady-state condition (which is equivalent to standing crop), then the Israeli beachesare 1.8-68 times more polluted than those of Florida and Texas and 19 times more than those of Bermuda. Basedon field observations,the author is of the opinion that it takes lessthan a year for the tar quantity on the beach to get to a steady-state condition. Therefore, the above assumptionwould distort the comparison so that the tar quantity on the Israeli beaches would be smaller in that comparison. The conclusion is, therefore, that the Israeli beaches are much more polluted than the beacheslisted in Table 3. The large quantity of tar on Israeli beachesis undoubtedly due to the heavy pollution of the Mediterranean with oil. Horn et al. (1970) report on an averageof 20 mg mW2of pelagic tar on the surface of the Mediterranean with a maximum of 540mg mR2. According to Butler et al. (1973)~ this is the highest concentration of pelagic tar in the world, the global averagebeing 3 mg m- 2. Quantitative
distribution
of tar in space and time
The results of this study do not provide a clear explanation of the fluctuation of tar quantity in space and time. We can, however, examine some of the factors which influence tar distribution in light of our results. OiZ trufic. Figure 4 showsthe lanes of oil trafhc in the Mediterranean. During the first 2 months of this study, as well as 8 years before it started, the Suez Canal was closed. The quantity of oil shipped through the canal immediately after its opening wasvery small. The influence of this lane on the Israeli coast during our study must therefore have been very limited. The only oil trafhc lane that could causepollution to the southern part of the Israeli coastis the one connecting the terminal of the Elat-Ashqelon oil pipeline with Europe. The heavy transport of oil in the East Mediterranean is along the routes betweenthe oil terminals of Syria and Lebanon and Europe. This heavier oil traffic in the northern part of the eastern Mediterranean is reflected in the heavier pollution of tar balls on the central and northern beachesof Israel. Distribution of tar balls in the sea.Oren (personalcommunication, 1970)collected tar during four cruises in the eastern Mediterranean in 1970 and 1971. He reported his findings in
274
A. Golik
relative rather than absolute terms. In all these cruises, high concentrations of tar balls were found between Cyprus and the Lebanese coastline. Oren (1970) relates these concentrations to the geostrophic currents which prevail in this area. They form a gyre with a no-motion area between Cyprus and Lebanon, and in this no-motion area the tar is concentrated. During storms, this area feeds the Syrian, Lebanese and northern Israeli coasts with tar. Distribution of dissolved and dispersed petroleum hydrocarbons in the sea. High concentrations of dissolved and dispersed petroleum hydrocarbons in the sea should indicate loci of oil spillage9 and hence loci of tar ball origin. Between 1977 and 1979, Oren & Ravid (in preparation) conducted six cruises to the eastern Mediterranean during which dissolved oil compounds were measured. High concentrations were found in two areas: between Cyprus and the Israeli-Lebanese coastline and west of Cyprus (Figure 4). The first location is identical to the area in which a high concentration of tar balls was found, and the other is in the area where discharge of oil into the sea is permitted. Sources of tar. Shekel & Ravid (1977) studied the sources of tar balls on the Israeli beaches based on the chemical composition of the tar balls. These workers analysed 788 tar balls which were collected fortnightly between 1973 and 1975 from eight stations along the Israeli beach. It was found that 76% of the tar balls were formed from crude oil and crude oil sludge, and 22% from fuel oil. Furthermore, on the basis of the nickel : vanadium ratio and sulfur content of the tar balls, it was found that practically all of the tar (96%) was formed from oil of the Persian Gulf or from the Gulf of Suez. No tar balls with the chemical composition characteristic of Libyan oil were found. The distribution of tar balls and dissolved oil compounds in the sea, the routes of oil transport in the eastern Mediterranean, and the origin of the tar balls which pollute the Israeli coastline indicate that the source for most of the tar pollution is between Cyprus and the Israeli-Lebanese coast. It is harder to explain the fluctuation of tar concentration as a function of time. The continuous decrease in tar quantity from 5635 g m-l in July 1975 to 1344 g m-1 in February 1976 could be a result of an event occurring at that time (reduction on oil shipment I, enforcement of regulations against oil spillages 7) which caused this decrease. Alternatively, this may be a phenomenon which repeats itself every year, causing cycles in tar quantity. A longer period of sampling is required to find whether such a cycle indeed exists. Tar behaviour and fate on the beach On the basis of data collected and observations made during this study, the processes which control tar ball distribution on the beach may be described as follows. Tar balls are formed by the evaporation of the light fractions of oil compounds which were spilled into the sea. The floating tar balls are driven by the winds, waves and currents onshore. Once landed on the beach, sand grains, shells and beach pebbles are attached to the tar ball, increasing its specific gravity. Therefore, tar balls which land on the beach can no longer float and may be found either in the water column or on the bottom. The hydrodynamic characteristics of the tar balls are such that the waves force them back to the shore. Searches for tar balls on the sea bottom beyond the breaker zone were conducted several times by divers and only very rarely was a tar ball found on the sea bottom. It may therefore be concluded that the eventual fate of the tar balls is to land and remain on the beach. Once on the beach, tar balls concentrate along the swash marks and move landward with the rising tide. Each successive higher tide, wave or storm causes a further landward move-
Distribution
and behaviour of tar balls
275
ment of the tar towardsthe backshore.The result is the concentration of tar on the backshore asseenin Figure 3. Occasionally, tar may be found on or near the waterline, indicating that its landing occurred just a short time previously. In the courseof this study, a large concentration of tar balls wasfound on the waterline on 12 May 1976.Thesetar ballswere very soft, uniform in shapeand size and created a continuous line of tar balls more than 50 km long north of Tel-Aviv. This undoubtedly resulted from an event of tar pollution by a ship or oil tanker that spilled its bilge water or oil sludgewhile passingalong the coast a few hours earlier. Indeed, chemical analysesof this tar showedthat it still contained paraffins down to C,, which normally evaporate within a day after spillage. On the next day, the sametar was still distinguishableas a continuous line of tar balls. It had, however, already moved several meters landward, was partly covered with sand, and had started to be incorporated into the rest of the tar population. On the beach, in the foreshore zone, the tar cannot be buried becauseeach time a wave runs up the beach it stirs up the beach material. The tar, being lighter than the sand, settles after the sandand remainson the beachsurface. Beyond the foreshore,the tar may be buried by the sandwhich is blown on the beach. The burial is to a depth of 50-70 cm but not for an extended period of time. During the winter, when storms occur, the author observed the waves swashthe whole beach and reach the foot of the cliff. These waves unearthed the buried tar and moved it both in an on-offshore direction and in a longshoredirection. The tar ballsmove along the shoreuntil they reach a point where there is no coastal cliff, such asa river valley or estuary. There, the wavesmay penetrateinland to a distanceof 200-300 m from the beach, carrying the tar with them. The seawaterwhich carries the tar to that distancelandward percolatesinto the sand on its way to the seaand there is no mechanism to carry the tar back to the beach. River valleys or other topographical depressionsin the backshoreserve asfinal traps for the tar [Plate r(a) (b)]. In order to get someideaabout the final fate of the tar, a fresh tar ball wasplacedon a cliff ledge so that waves could not reach and remove it. During the seven months that the ball stayed there, a hard skin was created around it; then the ball shrunk and becamemore brittle with increasing fissures all over it. Finally it started to disintegrate into 2-3 mm fragments that were shred off the ball and dispersedby the wind.
Summary
and conclusions
Measurements of tar quantities along the Israeli coastlineshowedthat between April 1975 and June 1976the averagetar content on the beachwas 3625 (S.D. = 2834)g m-l of frontal beach. This may serve as a referencevalue for comparisonwith future studies.Examination of tar data from various beachesin the easternMediterranean suggeststhe influence of an oil and sludgedump site in the seawest of Cyprus. Tar content on beachescloseto that dump site, such as Alexandria, Egypt, or Paphos, Cyprus, is an order of magnitude higher than that of beachesalong the easternshoresof the Mediterranean Sea. Comparisonbetweenthe Israeli beachesand somebeachesin North America showsthat the former are more polluted. This is not surprising in view of the heavy oil trafhc in the Mediterranean (23o/oof the world trafhc in 1975 according to Le Lourd, 1977) which causesthis seato be the most oil polluted in the world (Butler et al, 1973; Osterberg & Keckes, 1977). Comparisonof tar quantities amongthe various beachesof Israel showsthat the northern and central coastsof Israel are more polluted than the southern coast. This appearsto be due to a combination of oil shipping lanes and oceanographicconditions which causehigh concentrations of dissolved oil and tar lumps between Cyprus and Israel and Lebanon. A continuous decreasein tar
Cb)
Plate I. T ar accumulation on Bet Yannay beach following a winter storm. (a) on a cliffed beach. (b) Further along the beach from (a) where no cliff exists. Notice lack of tar in (a) and abundance of tar balls in (b).
A. Golik
276
quantity was found between July 1975 and February 1976, but no explanation for this can be offered at present. After landing on the beach, the tar balls are pushed to the back of the beach by each successive wave, tide or storm. During severe storms, it was noticed that tar balls are carried by longshore currents along the beach until they reach a low-lying land at the back of the beach. There, during storms, the waves may carry the tar balls zoo-300 m inland and there is no mechanism for their return. It is proposed that finally the tar is either buried by windblown sand or dries and mechanically disintegrates into small particles which are then dispersed by the wind. Acknowledgements Thanks are due to Y. Tandler and R. Holzer for their assistance in the field and laboratory work. A. Back, D. Bowman, V. Goldsmith, Y. Mart and A. Tandler critically read the manuscript and offered useful comments. This study was supported by the Israeli Environmental Protection Service. References Butler,
J. N.,
Morris,
B. F. & Sass, J.
Bermuda pp. Curtis, M. & Saner, A. 1974 Tar ball loadings on Golden Beach, Florida. Natiunal Bureau of Standards Special Publication No. 409. pp. 79-81. Dennis, J. V. 1959 Oil pollution survey of the U.S. Atlantic coast. 1973
Pelagic
tar from
Biological Slation Research Special Publication No.
and Sargasso
Sea.
Bewcuda
IO. 346
U.S. Departmezt of C%nmerce, American Petroleum Institute
Publication No. 4054. Dwivedi,
S. N. & Parulekar,
A. N. 1974
Oil pollution
Commerce, National Bureau of Stanabds Horn,
M.
H., Teal,
J. M. & Backus,
R. H. 1970
along
coastline. U.S. Department of pp. IOI-105. on the surface of the sea. Science 168,
the Indian
Special Publication No. Petroleum
lumps
409.
245-246.
Landes,
K. K.
1973
Mother
Bulletin 57,637-64x.
nature
as an oil polluter.
American Association of Petroleum Geologists
Le Lourd, P. 1977 Oil pollution in the Mediterranean Sea. Am& 6,3X7-320. Nelson-Smith, A. 1973 OiI Pollution and Marine Ecology. Plenum Press, New York. 260 pp. Okera, W. 1974 Tar pollution of Sierra Leone beaches. Nature 252,682. Oren, 0. H. 1970 Tar pollution of the Levant Basin. Marine Pollution Bulletin I, 149-ISO. Osterberg, C. & Keckes, S. 1977 The state of pollution of the Mediterranean Sea. An&o 6, 321-326. Ray, S. M., Oja, R. K., Jeffrey, L. M. & Presley, B. J. 1974 A quantitative and qualitative survey of oils and tars stranded on Galveston Island beaches. Department of Transportation, U.S. Coast Guard Report No. CG-D-10-75. Shekel, Y. & Ravid, R. 1977 Sourcea of tar pollution on Israeli Mediterranean coast. Environmental Science and Technology II, 502-505. United Nations Environment Programme 1980 Summary reports on the scientific results of MED POL, Part I. UNEP/IG II/INF 3. 202 pp.