grab samples

does not include oxygen demand by inorganic components. In cases where the sediment has been
dredged from low-oxygen sediments, most metals exist as sulfur compounds and will probably create a
high inorganic chemical oxygen demand when exposed to seawater of normal oxygen levels.
References
AMERICAN PUBLIC HEALTH ASSOCIATION. AMERICAN WATER WORKS ASSOCIATION. AND WATER POLLUTION CONTROL FEDERATION.
1975. Siandard methods ror the examinalion or water and wastewater. 14th ed. Washinglon. D.C. I 193 p.
7.4 Biochemical Oxygen Demand (BOD)
The biochemical oxygen demand (BOD) determination is an empirical test in which standardized
laboratory procedures are used to assess the relative oxygen requirements of wastewaters, effluents and
polluted waters. Using results obtained, in the highly artificial and confined condition of the laboratory, to
predict oxygen demand on the part of microorganisms and some chemical substances if present in the open
marine environment, seems so unrealistic that the procedure is not pursued here. A detailed account of the
test as used where applicable is given in APHA et al. 1975. The interactions between microorganisms and
dumped sediments is a subject of great interest, but it requires a more perceptive approach.
References
AMERICAN PUBLIC HEALTH ASSOCIATION. AMERICAN WATER WORKS ASSOCIATION. AND WATER POLLUTION CONTROL FEDERATION.
1975. Standard methods ror the examination or water and wastewater. 14th ed. Washington. D.C. 1193 p.
7.S Oxidation-Reduction Potential
I. Theory
The oxidation-reduction (redox or E h ) potential is defined as the electromotive force developed by a
platinum electrode immersed in the bottom sediment referred to the standard hydrogen electrode or a
reference electrode of known E h . A more complete theoretical discussion of Eh can be found in Berner
( 1971 ).
The value of Eh can be considered as a measure of the oxygen potential of the bottom sediments. A
positive value for Eh indicates the sediment is in the oxidized state or oxygen is present, whereas a negative
Eh indicates a reduced sediment. However, a number of electrochemical problems can seriously affect the Eh
values. Further, there is some discussion as to whether the E;, measurement should be taken in situ or the Eh
should be taken after the sediment has been brought into the laboratory. However, this latter process will
inevitably expose the sediments to the atmosphere and, therefore, significantly alter the sediment redox
potential.
The best method would be measurement in situ, but this is often not practical. Redox potential should
be measured as soon as possible after samples are collected. A number of chemical reactions can" poison"
the platinum surface or significantly affect the Eh measurement. Although the redox measurement concept
is commonly used in field studies, the values reported can only give an approximate concept of the redox
potential of the sediments. Since most sediment-seawater reactions occur within the interstitial waters at
the particle surface (not the total sediment-seawater interface), the "gross" measurements described here
give only an integrated approximation.
n. Equipment
Potentiometer (many pH meters also measure millivolts)
Saturated potassium chloride calomel cell
Platinum electrode with clean platinum surface
71