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SECTION 7 CHEMICAL TESTS WHICH MAY AID IN INTERPRETATIONS UNDER SCHEDULE III Several tests have been devised to assess such items as reactivity of sediments with seawater, oxygen stripping of the water column by either chemical or biological processes, and the relative ease with which sched uled items might be released to the water column during disposal of dredge spoils. The tests are artificial at best, but do constitute a first step beyond the determination of what is present and in what quantities. 7.1 Seawater Reactivity There has been considerable debate among marine geochemists as to the best method of determining the degree of interaction between sediments and seawater. Depending on the size characteristics of the dumped sediment and the degree of dispersion upon dumping, the ratio of interaction of the sediment with the water column and the degree of desorption from or adsorption of pollutants to the sediments can be highly variable. The original concept of the elutriate test was an effort to quantify the changes that might result when dredge sediment is dumped at a marine disposal site. However, the test is only a simulation of actual conditions. The emphasis throughout the test has been on keeping the seawater/sediment mixture well oxygenated so that all trace meta ls remain relatively insoluble. In the natura l environment these highly oxidizing conditions may not exist, and there may be some trace metal dissolution into the water column. The dumping of heavily polluted material from an anoxic sediment area may create a high chemical demand for oxygen from the overlying waters and neighbouring sediments, as the new chemical equilibrum is approached. This type of chemical oxygen demand is very hard to quantify or even define. The basic concept behind leaching tests, elutriate tests or seawater reactivity tests is the determination of how readily the pollutants in the sediments move back into solution in the overlying waters. For example, the preferred method to date for metal determinations has been total dissolution of the sediments. However, this method includes metals adsorbed onto the sediments, organometallic complexes adsorbed onto the sediments, metals contained within day structures, and metals forming part of the basic crystal lattice structure of the sediment minerals. A more reasonable value for" pollutant" metal concentrations might be determined by leaching techniques (Malo 1977). However, much more research is needed to determine what met-a l fraction truly represents the" poIlu ting fraction." Much of the reactivity of sediment with seawater is determined by reactions at the seawater/sediment interface, and, therefore, pollutant concentrations on the sediment particle surface are important when considering seawater reactivity. Recent investigations have shown that bulk chemical concentrations predict very different chemical reactions and equilibria than those actually found (MacKnight 1976). In conclusion, it is suggested that" relatively short-term" experimen ts be carried out where seawater is interacted with the sediment under conditions simulating the natural environment as closely as possible. The design of the experiment should allow for longer time periods of interaction than those specified in the elutriate test. The results of such seawater interaction experiments would probably yield a better assessment of the-pollution factor of heavy metals and perhaps other pollutants. References MACKNIGHT, S. D . 1976. Phosphorite solubility behavior in seawater. Ph.D. diss. Dalhousie University, Halifax, N.S. t 60 p. MALO, B. A. 1977. Partial extraction of metals from aquatic sediments. Environ. Sci. Tech. It: 277 - 282. 67
7.2 Elutriate Test I. Theory The objective of the test is to simulate the interaction of dredged sediment with disposal site seawater in an effort to determine the amount of polluting material ( pesticides, petroleum hydrocarbons, heavy metals, nutrients) that might be released to the water column where the dredged material is dumped. Comparison of the contaminant levels in the disposal site seawater before and after mixing with sediment determines the degree of contamination and how adverse the effect of dredge disposal might be on the disposal site. Although at present the water to sediment ratio has been set at 4: I, because of the quantities of liquid required for pesticide analysis, the procedure below will be outlined on a recommended 20: I ratio. (For a more complete discussion, see Lee et al. 1975 ). II. Summary of Method A ratio of 20 parts water (disposal site) to 1 part sediment (dredge site) for a lOlal of abou t 4-/ mixture is agitated by air bubbling. (The aeration of the sample is performed in an attempt to duplicate likely conditions during dumping. It should be noted, however. that this may cause some loss of volatile components e.g. low molecular weight hydrocarbons). The mix is allowed to settle and the supernatant is centrifuged and filtered. Analyses of the water before and after and the sediment before and after mixing is made for pesticides. petroleum hydrocarbons, heavy metals and nutrients. A physical analysis of the " before" sediment is also necessary. III. Apparatus and Reagents Graduated cylinders 6-/ Erlenmeyer flasks Coarse glass air diffusor Gas washing bottle Clean source of compressed air, with traps in line to further clean supply. Mem brane filters (0.45-fLm land filtering apparatus (glass) Centrifuge (2000 rpm) Equipment for sieve and pipette analyses. See Section 5. Note: All glassware must be thoroughly soaked in 10% (V IV) hydrochloric acid solution. Presoak all filters in 5 M hydrochloric acid solution for 2 h prior to use. Rinse everything thoroughly with deionizeddistilled water. IV. Procedure (Lee et a l. 1975) (I) Combine"'" 200 ml of wet sediment with enough disposal site water (unfiltered) to bring total volume to 4/ in 6-/ Erlenmeyer graduated flask. Because of the volumes that may be necessary for analytical testing of the wa ter <strong>samples</strong>, it is suggested tha t the test be run in duplicate simultaneously; one portion for metals and petroleum hydrocarbons; the other portion for pesticides. Half of one bottle of sediment should be used for elutriate; the other half used for the " before" analysis. The" before" seawa ter should be filtered through a 0.45-fLm filter and saved for analysis (see below). (2 ) Thoroughly agitate mixture by bubbling air through mix for 1/2 h. Allow to settle for I h. Carefully decant off liquid. (3) Centrifuging the water before filtration will assist in speeding up the filtration procedure. (4) Filter water through 0.45-fLm filter . Vacuum or pressure filtration may be used to speed up process. 68
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SHELVED WITH SERIAtS no. 1
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· Available from : Scientific Info
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FOREWORD On December 13, 1975, the
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ABSTRACT WALTON, A. (ed. ).1978. Me
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5. Organosilicon compounds 6. Cyani
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The consolidated core sample in the
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drive the core barrel through sand
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2.4 Field Notes; Labels for Sample
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SECTION 4 SAMPLE STORAGE Stored sed
Page 30 and 31: 5.1.4 Dry Coarse Fraction The coars
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Page 38 and 39: SECTION 6 CHEMICAL ANALYSIS This se
Page 40 and 41: IV. Reagents Concentrated high puri
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Page 44 and 45: (I) Place 220 ml of solution in a 5
Page 46 and 47: Flameless: 0.000 I mgll (solution)
Page 48 and 49: Chelating reagent: ammonium pyrroli
Page 50: B. Reagents Chelating reagent: ammo
Page 54 and 55: efore use. Then rinse with conc. hy
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Page 60 and 61: B. Proced ure (\) To 50-ml portion
Page 62 and 63: (5) Analyze the extract or a suitab
Page 64 and 65: will probably involve the analysis
Page 66 and 67: = O.S ml (40°C water bath, use a s
Page 68 and 69: A 9lA-cm column of 10% OV -Ion SO-I
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Page 72 and 73: (3) Extract benzene extracts from (
Page 74 and 75: VI. Analysis (Coburn et al. 1976) A
Page 76 and 77: analysis is its inability to analyz
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