Effects of water-soluble fractions of crude oil and dispersants on nitrate generation by sandy beach microfauna

Marine Pollution Bulletin, Vol. 13, No. 8. pp. 287-291, 1982

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Effects of Water-soluble Fractions of Crude Oil and Dispersants on Nitrate Generation by Sandy Beach Microfauna BERYL HARTY and ANTON McLACHLAN

University of Port Elizabeth, P.O. Box 1600, Port Elizabeth, 6000South Africa

Effects on sandy beach microfauna of soluble pollutants, such as might be associated with an oil spill, were investigated in terms of nitrate generation. Nitrate generation by the microfauna in small sand columns in the laboratory was severely inhibited by water-soluble fractions of crude oil, dispersant and oii/dispersant mixtures in order of increasing effects. Short-term effects of such pollutants on nutrient regeneration by exposed sandy beaches are discussed. Oil pollution on South African beaches was brought to the attention of the public in 1970 when the Wafra ran aground off Cape Agulhas. In 1977 the Venpet and Venoil collided off the south coast in the Victoria Bay area and crude oil covered both sandy beaches and rocky shore at the height of the holiday season. Oil pollution of exposed sandy beaches along the south coast of South Africa is thus a reality today. Sandy beaches make up most of the South African coastline and are important for two reasons; for filtering seawater to the extent of 1061 per metre shoreline per day (McLachlan, 1977) and, in this process, for the regeneration of inorganic nutrients, for example phosphate and nitrate. As part of a general study of oil pollution on sandy beaches, the physical effects of crude oil on water flow through beach sand have already been investigated (McLachlan & Harty, 1981). In general, it was concluded that oil has little effect on water filtration through exposed beaches. More recently, toxic effects of crude oil on the meiofauna of an exposed beach were assessed. Recovery was found to be within five months under most treatments (McLachlan & Harty, 1982). This paper reports on the last phase of this work. It aims to assess the effects of water-soluble fractions and dispersant on the beach microfauna whose main role is in nutrient generation. Because nitrogen is often the growthlimiting factor in phytoplankton production, it was decided to study the effects of oil on the nitrogen cycle in beach sand. Sand columns were designed to simulate a natural beach system in the laboratory and nitrate generation (nitrification) was studied as a measure of activity and the basis against which to measure oil pollution.

size 180-220/~m. This quartz sand is well sorted and has a high calcium carbonate content. The beach is prograding with a well developed berm averaging 50 m wide (McLachlan, 1977). Small sand columns were designed in order to provide simple and rapid evaluation of the relative effects of pollutants on nitrate generation (Fig. 1). An inverted glass funnel was placed in a 500 ml glass beaker and raised slightly. A perforated plastic disc fitted over the stem of the funnel and was glued to the beaker walls with a silicon glue. The upper half of the beaker, on top of the disc, was lined with 200/~m plastic mesh to contain the sand and prevent leakage. This created a layer of sand through which water could filter. Circulation of water was achieved by inserting a pasteur pipette into the glass funnel and bubbling air through it and the funnel. A measured volume of sand (200 cm 3) and water (250 cm 3) was placed in each column and the top loosely covered with 'parafilm' to prevent evaporation. Experiments were run for 40 h at 20°C and water samples were taken after 20 and 40 h. Nutrient analysis for total nitrogen, ammonia, nitrite and nitrate was done using a Technicon Auto-Analyser. Samples were first digested on a block digester at 150°C for 1 h and 390°C for 30 min., for total nitrogen. Amino acid (glycine) was added to produce an organic nitrogen level of l mg.N.1-1 in the original solution. This provided a substrate for mineralization and nitrate generation. Prior to starting the experiments, a profile through the intertidal zone on King's Beach was sampled to locate the

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Materials and M e t h o d s For these experiments sand was collected from a local beach, King's Beach, near Port Elizabeth. This is a moderately exposed beach and has sand of medium grain

MINIATURE SAND COLUMN

Fig. 1 Diagram of a sand column.

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Marine Pollution Bulletin

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Fig. 2 Profile through King's Beach to show nitrate generation at different positions. Contour lines of equal nitrate generation drawn by eye. Values given as nitrate expressed as a percentage of total nitrogen.

part of the sand body with greatest nitrifying activity. Samples of sand were taken at the low, mid and high tide levels at different depths. A 40 h run was done using duplicate columns of sand from each part of the beach to compare relative nitrification rates. Consequently sand from the place where the greatest nitrification was recorded was used for further experiments in the laboratory. From previous work (McLachlan et al., 1981) the flow rate was found to be extremely important in sand column construction and directly influenced interstitial activity. In these miniature systems, however, the flow rate could not be accurately controlled and the mineralization values were higher than those under controlled rates. However, this is intended as a relative and not an absolute measure. The constant air bubbles caused the water in the beakers to be supersaturated with oxygen.

16

Three different experimental runs were done using (1) water soluble fractions (WSF), (2) dispersant and (3) WSF plus dispersant mixtures. The dispersant used was Chemserve OSE 750, a solvent-based emulsifier. WSF were extracted by stirring a layer of 500 ml of fresh crude oil (Arabian light) on 4.51.0.451am filtered seawater for 22 h in a glass container using a magnetic stirrer. Four dilutions of dispersant and of this polluted water were made with filtered seawater for the first two experiments, respectively. For the final experiment 50 ml of dispersant and 450 ml of crude oil were mixed and stirred for 22 h to produce an emulsion. Five dilutions of this were then run through the columns for 40 h. WSF were measured using a modified version of the method in A P H A (1975). Extraction with carbon tetrachloride was as follows: 250 ml of sample was shaken in a separating funnel for 2 min. with 1.25 ml of hydrochloric

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Volume 13/Number 8/August 1982

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acid (1%) and 10 ml of carbon tetrachloride. It was allowed to separate for 5 min. before the carbon tetrachloride was tapped off through phase-separating paper into a 50 ml volumetric flask. The procedure was repeated three times with the addition of carbon tetrachloride to the sample. The filtered carbon tetrachloride was then made up to 50 ml and the sample was scanned on an infra-red spectrophotometer over 3200-2600 cm -1.

Results Figure 2 shows nitrate production rates in different parts of King's Beach as recorded in the initial experiment using sand from three levels of the intertidal zone. Greatest

activity was recorded at the mid tide level at about 20 cm depth. This is close to the part of the beach experiencing maximum water filtration during the incoming tide and consequently sand from this part of the beach was used for subsequent experiments. Results of the first experiment using WSF are illustrated in Fig. 3. The initial concentration of the WSF in the prepared solution was 14.4 mg 1-1. After 20 h 80-90% of WSF are generally lost (Anderson et al., 1974) and in these experiments none could be detected after 40 h. Results are given as the increase in nitrate nitrogen over the experiment expressed as a percentage of the amino acid nitrogen added. After 20 h the nitrate ratios had all decreased except in the lowest concentration of WSF (0.28 mg 1-1). However, by40 h

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289

Marine Pollution Bulletin all values had decreased to almost zero and, in fact, nitrate removal occurred. Because the final nitrate values dropped below initial values this resulted in negative values on the graph. The lowest values, about - 10°70, reflect the virtual absence of nitrate at the end of the experiment. Ammonia values remained fairly constant (ca 0.04 mg. NH4-N 1-~) with a slight decrease after 40 h while total nitrogen values decreased after 40 h (from 1.6 to 0.2 mg N 1-~). Nitrite values were negligible throughout (not tabled). In the second experiment (Fig. 4) using Chemoserve OSE 750 in concentrations between 0.01 ml 1-l and 10 ml 1-1 ammonia levels rose with an increase in dispersant concentration, but never exceeded 0.975 mg NH4-N 1-i. This was directly due to the chemical nature of the dispersant. A slight decrease was seen after 40 h. Nitrate values decreased after 20 h with little difference between the 0.01 ml 1- l and 0.1 ml 1- l values. After 40 h all dilutions of dispersant caused a large decrease in nitrate values and nitrate removal occurred. In the final experiment, using a mixture of WSF and dispersant, the WSF extracted was much more concentrated than in the first experiment (Fig. 5). Unfortunately, readings could not be taken on the infra-red specrophotometer as the dispersant turned milky when mixed with water. Nitrate values decreased dramatically after 20 h and were very much the same after 40 h, the ratio ranging between -8°70 and -9.75°70. Ammonia values were slightly higher after 40 h (less than 0.9 mg NH4-N 1-l) and increased with an increase in dispersant concentration (from 0.080 mg NH4-N 1-l to 0.960 mg NH4-N 1-1) due to the chemical nature of the dispersant or the mortality of the fauna. Total nitrogen readings decreased after 40 h. All nitrite values were very low throughout (0.001 mg NO2-N 1-1 to 0.01 mg NO2N 1- l), as in the previous two experiments.

Discussion Hodson et al. (1977) followed the assimilation and mineralization of ~4C-labelled glucose and the effect of oil on bacterial activity in water. They found that concentrations of WSF above 300/ag 1- ~could significantly inhibit marine bacterial activity. Our results showed severe inhibition of nitrification at 280/ag 1- ~, which was our lowest concentration. As Gordon & Prouse (1973) measured total hydrocarbon concentration of up to 800 tag 1-1 beneath oil slicks, these values are well within the recorded range following a spill. Griffin & Calder (1977) found that WSF was more toxic than the parent unweathered crude oil and that it reduced the growth rate of a marine bacterium, Serratia marinorubra, in batch culture. They did not, however, find a correlation between toxicity and concentration of total WSF or of aromatic hydrocarbons and WSF. Calder & Lader (1976) found that dissolved aromatic hydrocarbons decreased growth rate and cell density of marine bacteria in batch culture. WSF was clearly inhibitory to nitrate production in these experiments. At the lowest concentration of WSF used, 0.28 mg 1-1, nitrate production was inhibited by 83°70 after 40 h. The highest concentration of WSF (14 mg 1- l) resulted in 98°7o inhibition. Above 1.4 mg 1-1 the nitrate production ceased within 40 h. These experiments using different dilutions of dispersant clearly indicated complete inhibition of 290

nitrification within 40 h at all concentrations used and nitrate was actually removed within 20 h at the higher concentrations. This may be due to a protein skimming effect because of foaming. The WSF/dispersant mixture was clearly a toxic combination with almost total inhibition within 20 h in even the 16 x dilution (6.25 %). The simple miniature sand columns used here have been found to provide a rapid and simple, closed system for relative measurement of interstitital processes, in this case nitrification. While they lack the sophistication and accurate simulation of in situ conditions of larger column systems (McLachlan et al., 1981), they provide a rapid relative measure with a reasonable degree of repeatability. However, because they represent a closed system they have certain limitations. In the natural beach environments the chance of recovery from pollution by soluble fractions of oil or dispersant would be good because of the high energy nature of the beaches and the constant filtration of new sea water. It has been shown that fresh crude oil plus dispersant mixtures are rapidly washed out of beach sand by wave action (McLachlan & Harty, 1981). Once the fauna is destroyed in a closed system, such as these miniature sand columns, recolonization cannot occur even if fresh unpolluted water is added. Consequently these experiments represent only a relative, short-term evaluation of the effects of soluble pollutants. Recovery of the columns over longer periods was not evaluated. It should be reasonable to assume, however, that under natural conditions on exposed beaches, such as occur around the South African coastline, soluble pollutants would seldom remain in the vicinity of a single site for more than 48 h and in general would be rapidly dispersed and removed by wave action in considerably shorter periods. Soluble pollutants such as might be associated with an oil spill may be concluded to have drastic short-term effects on nitrate generation by beach microfauna. Water-soluble fractions had the least effect, dispersant had greater effect and water-soluble fraction/dispersant mixtures had the greatest effect. Clearly dispersants should not be used near beaches, because of the toxicity of this mixture.

We thank the South African Council for Scientific and Industrial Research and the Universityof Port Elizabeth for financial support, Mrs A. J. Gerber for typing the manuscript, Mr N. Malan for help with oil analysisand MissM. Mareefor preparing the figures.

Anderson, J. W., Neff, J. M., Cox, B. A. & Tartam, H. E. (1974). Characteristics of dispersions and water soluble extracts of crude and refined oils and their toxicityto estuarine crustaceans and fish. Mar. BioL, 27, 75-88. APHA (1975). Standard Methods for the Examination of Water and Wastewater, 14th ed. AmericanPublic Health Association, Washington, D.C. Calder, J. A. & Lader, J. H. (1976). Effect of dissolved aromatic hydrocarbons on the growth of marine bacteria in batch culture. Appl. envir. Microbiol., 32, 95- 101. Gordon, D. C. & Prouse, N. J. (1973). The effectsof three oils on marine phytoplanktonphotosynthesis.Mar. Biol., 27, 329-333. Griffin, L. F. & Calder, J. A. (1977). Toxic effect of water soluble fraction of crude, refined, and weathered oilson the growthof a marine bacterium. Appl. en vir. Microbiol., 33, 1092-1096. Hodson, R. E., Ajam, F. & Lee, R. F. (1977). Effects of four oils on marine bacterial populations: Controlled ecosystempollution experiment. Bull. Mar. ScL, 27,423-430.

Volume 13/Number 8/August 1982

McLachlan, A. (1977). Volumes of seawater filtered through East Cape sandy beaches. S. Aft. J. Sci., 75, 423-430. McLachlan, A., Dye, A. & Harty, B. (1981). Simulation of the interstitial system of exposed sandy beaches. Estuar. Cstl Shelf Sci., 12, 267-278.

McLachlan, A. & Harty, B. (1981). Effects of oil on water filtration by exposed sandy beaches. Mar. Pollut. Bull., 12, 374-378. McLachlan, A. & Harty, B. (1982). Effects of crude oil on the supralittoral meiofauna of a sandy beach. Mar. envir. Res. (in press).

MarinePollutionBulletin, Vot. 13, No. 8, pp. 291-292, 1982. Printed in Great Brilain

Garbage from Ships S/r, With reference to the report by Paul V. Horsman (Mar. Pollut. Bull., 1982, 13, 167-169)entitled 'The Amount of Garbage Pollution from Merchant Ships', I would like to express some concern regarding several of the statements which purport to inform readers of the IMCO regulations arising from the 1973 Conference on Marine Pollution. Firstly, I would commend the author for the painstaking (and probably painful) manner in which he has executed the onerous task of collecting data for his analysis of the marine garbage problem. Indeed, his efforts would form an admirable base from which an incinerator could be designed. Secondly, however, I would caution any reader who has taken the article at face value in so far as the presentation of 'facts' arising from MARPOL regulations. The facts are these: (a) The MARPOL Conference did indeed take place during 1973. (b) The resulting Convention includes 5 Annexes, of which III, IV and V are optional. (Annex V deals with pollution by garbage.) (c) At the time of writing, insufficient Administrations have ratified the Convention to bring it into force. (A total of 15 countries representing at least 50°70 of the world's tonnage is required.) (d) Of those countries having ratified the Convention so far, some have specifically excluded Annex V. (e) MARPOL will only apply (when in force) to ships entitled to fly the flag of States which have actually ratified the Convention, or to other vessels operating under the authority of such a State. From these and other considerations, it can be deduced that it will be some time before Annex V enters into force. Therefore, to state that " . . . s h i p s . . , ignored or did not know about IMCO regulations regarding the dumping of g a r b a g e . . , etc." is quite incorrect. To elaborate upon the position, it is worth recalling that the MARPOL Convention was extremely ambitious in its aims and was consequently found to be extremely hard to convert into practical regulations. Indeed, some aspects are still proving to be technically extremely difficult to achieve, particularly in view of the effects and constraints imposed by the hostile marine environment. Despite this apparent atmosphere of uninterrupted gloom and despondency, there are some areas in the world where similar regulations do exist, but these are wholly within territorial waters and generally form part of bye-

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laws and harbour regulations. However, the overall position is still rather piece-meal at present. The aims of MARPOL are extremely laudable, but to use a simple parallel, we must learn to walk before we can run. It is to be hoped that all sections of the Convention are brought into force as and when the hardware, the Shipping Industry and Governments are both prepared and able to implement the Convention and that this date is sooner rather than later. On a lighter note, the suggestion that the supply of keg beer in preference to canned varieties would reduce the trail of metallic debris is arguable. It is my experience that the continuous movement of ships has a detrimental effect upon the quality of the beer and that such beer 'goes off' within two months of commencing its seagoing life. This subject could well prove to be an excellent basis for further investigation and research!

Oil Companies International Marine Forum, 6th Floor, Portland House, Stag Place, London SW1E 5BH, UK

PETER F. GILL

Environmental Impact Assessment We were most interested to read Dr Cole's editorial (Mar. Pollut. Bull., 13, 145-146, 1982), which criticized environmental impact assessment (EIA) as being too lengthy, and which suggested a quicker alternative. This editorial contained many apposite observations. However, we feel that cases where the assessment has been excessively drawnout and expensive, or where the final report has been so long as to be incomprehensible, should not be regarded as representative of EIAs as they are, or should be, carried out. We believe that EIA is very useful when sensibly applied. In fact, EIA is not only used as 'political eyewash'. Many companies, both in the UK and overseas, themselves commission EIAs because they genuinely wish to be appraised of the potential environmental consequences (both good and bad) of a development during its planning so that any necessary ameliorative or supportive measures can be incorporated into the development. In the case of such EIAs, it is necessary to match the scale of the assessment with the resources available for them, in terms of both manpower and finance. These EIAs must also be conducted within a commercially prudent time limit. We have certainly conducted studies within the 291