Adsorption of Polychlorinated Biphenyl onto Sea Bed Sediment, Marine Plankton, and Other Adsorbing Agents Yasushi Hiraizumi", Mieko Takahashi, and Hajime Nishimura Department of Chemical Engineering, The Faculty of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
Adsorption of PCB onto sea bed sediment, sand, and previously dehydrated samples of plankton and other adsorbing agents was experimentally examined and compared with the results of field observations. Samples of zooplankton and phytoplankton were observed to reach their maximum PCB adsorption capacity within 100 t 6 200 min. However, the desorption rate was very slow. Batch studies, as well as field observations, indicate t h a t PCB adsorption of various adsorbing agents correlates well with the PCB concentration in brine, and could be described by a Freundlich isotherm. T h e PCB concentration factors of the adsorbents were found to be inversely related to their average particle size and linearly related to their specific surface area for adsorbents of the same constituent. However, the organic content of the adsorbent also appeared to influence the PCB concentration factor.
I n recent years, an increasing number of analyses of polychlorinated biphenyls (PCBs) in marine plankton, sediments, and fishes have been conducted because of pollution by PCBs and their relation to accumulation phenomena (1-5). However, little is known about the mechanism of transport of PCBs in the marine environment. According to the few available studies, horizontal distributions of PCBs in water and in the sediment surface suggest that the role of sediment or suspended matter upon the transport of PCBs in coastal waters is important (5).PCBs were shown to accumulate more on suspended matter than on plankton (6).At the same time, PCB accumulation onto suspended matter and plankton in t h e marine environment was found to be correlated to PCB concentration in water, and could be described by a formula analogous to t h a t of a Freundlich plot (6). Concerning the latter, a forecast has been already given by a n adsorption experiment using clay minerals, sand, and soil samples ( 7 ) .The capacity of PCB adsorption upon suspended matter was also suggested to be mainly dependent upon particle size (6). As we have seen, t h e problem has been reduced to an experimental examination of PCB adsorption on marine sediment, plankton, and other adsorbing agents. This will complement t h e above-stated findings of the field observation, and the relevant characteristics of particles for PCB adsorption will also be determined. T h e objectives of this study are threefold: T o measure the PCB adsorption rate onto adsorbents, or to estimate the time necessary for attaining the equilibrium concentration through batch adsorption studies. T o ascertain experimentally PCB adsorption equilibrium between solid and aqueous phases, which has been observed in t h e field. To examine the general relationship between particle size, specific surface area, and PCB concentration factor of the adsorbent agents. Hopefully, a n outgrowth of this work will be the development of a model to predict the behavior of PCBs in the marine environment, taking into account the sorption of sediments a n d suspended matter and the hydraulics of their transport. Methodology
Materials. T h e PCB, KC-500, was a sample from Kaneka 580
Environmental Science & Technology
Chemical Co., and was used without further purification. The sediment, sand, plankton, activated carbon, and acid clay samples used in this study and their sources are given in Table I. Various types and contents of the sediment were chosen t o examine their effect upon the adsorbing ability of PCB. Activated carbon and acid clay were chosen for the sake of contrast. Experimental Studies. The adsorption studies were carried out by mixing an aqueous solution of PCB with a known amount of adsorbent agents. An n-hexane solution of PCB was mixed with 2 mL of ethanol and added to 400 mL of seawater. n-Hexane was used to rapidly disperse the PCB in the water phase, and ethanol was added to emulsify and dissolve it in t h e aqueous phase. A separatory funnel was kept on a shaker for 10 min t o disperse and emulsify the mixture. The various amounts of the added ethanol (0.03,0.1,0.5,and 2 mL) were examined, but the difference of the added amount was ascertained not to have any influence upon PCB partition between solid and aqueous phases. In these studies, the PCB concentration in the aqueous phase was controlled within 100 ppb. This value was less than t h e solubilities of PCB in the range of 0.3-3 ppm given by Zitko ( 8 ) ,but two times higher t h a n the solubility of -56 ppb given by Haque et al. ( 7 ) . T h e adsorption experiment was performed with the concentration of PCB varied and the amount of adsorbent agent held constant. A known quantity of adsorbing agent was weighed and added to the aqueous solution prepared in a funnel. The funnel was kept on the shaker for a certain period; the period of time for adsorption rate measurement varied with its stage, while the time for the adsorption equilibrium test was fixed. T h e samples for rate measurement were then centrifuged a t 3000 rpm, and those for equilibrium testing were allowed to settle for 24 h. T h e PCB content of 200 m L of the supernatant liquid was extracted in two stages using 25 mL each of n-hexane. The extract was concentrated to 3 mL by blowing down under a dry air stream after rectification. 'The adsorption of PCB on the surface of the container and loss of PCB by volatilization were accounted for by running a blank through the experiment. Loss by volatilization was negligible. T h e concentration of PCB remaining in solution was determined with a Hitachi series gas chromatograph (equipped with a Nifi3electron capture detector). The quantity of PCB was determined by taking into account the sum of all gas chromatographic peaks (9).The analytical procedure followed t h e method established by the Environment Agency of Japan (10).
T h e amount of PCB adsorbed, x , was calculated by the formula: where V is the volume of the aqueous solution, and C:! and C1 are the original and final net concentrations of the adsorbate. T h e net concentration of the adsorbate was determined through the use of a blank run. T h e specific surface area of the adsorbents was estimated by the vapor phase chromatographic method. The volume of adsorbed nitrogen upon the adsorbent was measured by sorptionmeter (Shimazu series), and the specific surface area was calculated by the equation of Brunauer, Emmett, and Teller ( 1 1 ) .
0013-936X/79/0913-0580$01.00/0
@ 1979 American Chemical Society
Table 1. Source of Materials under Investigation surface
lzumisano sediment
PHY T O P L b K T J N
1000-
source
e ' ( I
fine sea bed sediment collected off lzumisano in Osaka Bay, particle diameter is I * * * 104
10h
: 7..11. O F dS;\K.\ H A Y ' 7 4
/
/
si1 O F SCKF
