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Hales, J. M. Atmos. Environ. 1972,6,635. Ryan, P. A. M.S. Thesis, Department of Chemical Engineering, University of California, Los Angeles, Los Angeles, CA, 1984. Dullien, F. A. L. ”Fluid Transport and Pore Structure”; Academic Press: New York, 1979. Pearson, C. R.; McConnel, G. Proc. R. SOC. London, Ser. B 1975,189,305. Su, C.; Goldberg, E. D. In “Strategies for Marine Pollution Monitoring”; Goldberg, E. D., Ed.; Wiley: New York, 1976. “The World Book Encyclopedia”; World Book, Inc.: 1984; Vol. 17. Holzworth, G. C. “Mixing Heights, Wind Speeds, and Potential for Urban Air Pollution Throughout the Contiguous US.” EPA, Research Triangle Park, NC January 1972, Office of Air Programs Publication AP-101. Leighton, D., Jr.; Calo, M. J.. J. Chem. Eng. Data 1981,26, 382. Karickhoff, S.;Brown, D.; Scott, D. Water Res. 1979,13, 241. Foth, H.D.; Turk, L. M. “Fundamentals of Soil Science”; Wiley: New York, 1972. Mackay, D.; Bobra, A.; Shiu, W. Chemosphere 1980,9,701. Pierce, R.; Olney, C.; Felbeck, G. Geochim. Cosmochim. Acta 1974,38, 1061. Veith, G.; Defoe, D.; Berystedt, B. J. Fish. Res. Board Can. 1979,36,1040. Junge, C. E. Tellus 1974,26,477.
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Received for review October 17,1983. Revised manuscript received September 17,1984.Accepted December 10,1984.This work was supported in part by U.S. EPA Grant CR-807864-02.
Phosphorus-Zinc Interactive Effects on Growth by Selenastrum capricornut urn (Chlorophyt a James S. Kuwabara
Water Resources Division, US. Geological Survey, Menlo Park, California 94025
rn Culturing experiments in chemically defined growth media were conducted to observe possible Zn and P interactions on Selenastrum capricornutum Printz growth indexes. Elevated Zn concentrations (7.5 X and 1.5 X lo-’ M [Zn2+])were highly detrimental to algal growth, affecting lag, exponential, and stationary growth phases. P behaved as a yield-limiting nutrient with maximum cell densities increasing linearly with total P. This yield limitation was intensified at elevated Zn concentrations. Although calculated cellular phosphorus concentrations increased markedly with Zn ion activity, elevated Zn concentrations had no apparent effect on rates of phosphorus uptake estimated for Selenastrum during exponential growth. Results indicated that P-Zn interactions were significant in describing Selenastwm cell yield results and are consistent with previous Zn studies on chlorophytes. These P-Zn interactions and the observed inhibitory growth effects of submicromolar Zn concentrations suggest that in nature an apparent P yield-limiting condition may result from elevated Zn concentrations. Introduction
The degree to which soils and natural waters may support nutritional needs of biota is dependent on numerous interactive processes. Direct field application of results from laboratory experiments that monitor biological response to various concentrations of a single nutrient or toxicant may often be inappropriate because significant nutrient interactions are not understood. A growing body of information indicates that nutrient availability to biota involves interactions with physical, chemical, and biological parameters (1-4). An understanding of how and to what
extent these interactions affect organisms is essential in developing models that describe and predict environmental impacts. Interactions involving micronutrient availability, for example, have generated increasing environmental concerns (2,3).There may be only submicromolar differences between micronutrient concentrations that generate beneficial effects and those that impose growth (yield or rate) inhibition. Since Eiler (5)first demonstrated that zinc is essential for growth of Stichococcus bacillaris (chlorophyta), Zn2+has consistently been added to algal culturing media. Biochemical significance of zinc as a cofactor in numerous enzyme systems and in indoleacetic acid synthesis has been well established (6). Cases of zinc deficiency in algae have been cited by numerous workers (7-9). This essential micronutrient, however, may also induce toxic response at submicromolar activity (9,IO). Macrocystis pyrifera (phaeophyta) gametophytic growth is inhibited at a computed Zn ion activity of approximately M (11). Qne micromolar total Zn added to seawater (background total Zn -lo-’ M) reduced growth rates of M . pyrifera juveniles (12). Bartlett et al. (10) reported a noticeable increase in lag-phase duration of the freshwater chlorophyte Selenastrum capricornutum due to elevated trace metal (viz., copper, zinc, and cadmium) concentrations. Total Zn additions in the micramolar range to synthetic algal nutrient medium (SANM) (13) reduced 14-day cell yield of S. capricornutum by as much as an order of magnitude (14). This toxic Zn addition represented a Zn ion activity of M in SANM. Some suggestions in the literature indicate phosphorus (P), an essential macronutrient that often limits algal may have an interactive effect biomass in nature (15,16),
Not subject to U S . Copyright. Published 1985 by the American Chemical Society
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Table I. Selenastrum Culturing Data with 95% CI (n = 3 Treatment Replicates) for Nine Treatments at Various Initial P and Zn Concentrations
treatmentsa initial zinc concn initial phosphate concn (2.0 x (4.0 X (6.0 X (2.0 x (4.0 X (6.0 X (2.0 x (4.0X (6.0 X
104, 1 x lo4, 2 X lo*, 5 X 104, 1 x lo", 2 X lo*, 5 X 104, 1 x lo", 2 X lo", 5 X
10-11) lo-'')
lo-") lo-")
10-11)
( 0.995). The slope of mol the line, and Its 95% confidence interval [(15.0 f 2.1) X of P.cell-'.day-'], is an estimate of the P uptake rate for Selenastrum during exponential growth.
x2
trations were
