1973 - 1974 
Manker, J. P. (1975) Distribution and concentration of mercury, lead, cobalt, zinc, and 
chromium in suspended particulates and bottom sediments - upper Florida keys, Florida Bay 
and Biscayne Bay. Ph. D. Dissertation. Rice University, Houston, TX. 125 pp. 
Concentration of Pb, Hg, Cr, Co, and Zn have been determined in bottom sediments, the 
4-n fraction of bottom sediments, and in suspended particulates from the Upper Florida 
Keys/Biscayne Bay area. Highest concentrations are found in the 4-n and suspended 
fraction and may be related to more surface area being provided by fine particulates 
for adsorption/absorption of toxic metals. Organics associated with fine particulates 
also allow additional toxic metals, especially Hg, to be chelated or taken up in organic 
combinations. Toxic metal concentrations in suspended versus 4-|im fractions are 
similar as are their particle assemblages indicating the possible existence of chemical 
and physical equilibrium conditions between these fractions. Such equilibrium conditions 
could be disrupted by increased wave and/or current conditions which would place 
large volumes or bottom-derived material (4 ^ to 20 n) into suspension with associated 
toxic metals. A great potential exists during high winds for dispersal of this mobile 
fraction of bottom sediments concentrated in toxic metals to areas of low 
concentration. Because lagoonal environments contain large amounts of fine material, 
this process could take place to a greater extent. Even under normal wind conditions 
(~5 kts), two to three times as much fine material is in suspension in bay areas as 
compared to the reef tract areas. The mineralogy/chemistry of finer particles may 
play a role in toxic metal concentrations and distribution. In Biscayne Bay, which is 
mainly a sand-size quartz environment, high metal concentrations were predicted but 
low values were obtained. Immediately outside the quartz environment (i.e., on the reef 
tract) where CaC0 3 dominates, sediments high in concentrations of toxic metals were 
recorded. Such a discrepancy may be caused by calcium carbonate particles allowing 
toxic metals to be absorbed into the carbonate structure, where as the Si0 2 structure 
does not permit such substitution. Other reasons for low concentration of these metals 
in Biscayne Bay may be caused by the lack of fine particulates in this dominantly sand- 
size quartz environment for adsorption or absorption of metals, or perhaps most of 
these metals originate from outside the Bay. In general, toxic metal concentration in 
the study area can be correlated with areas of dense population with associated high 
automobile and boat traffic and improperly monitored and maintained sewage disposal 
systems. In addition, the Turkey Point nuclear/fossil fuel power plant may be linked 
with some metal concentrations. Pollutants (sewage and toxic metals) introduced in 
northern portions of the study area are able to move southward toward less populated 
areas by means of longshore drift and counter-currents present at the shelf margin. 
Highest toxic metal concentrations come from sediments receiving effluent from a 
storm sewer system in Tavernier Key, a marina on Key Largo, and a lagoonal area in 
Florida Bay. The latter two locations should be expected to yield high toxic metal 
concentrations because they are restricted basins in populated areas where these 
metals could accumulate. Metal concentrations are also noted near the Turkey Point 
generating facility for Hg, Zn, Cr, and Co. Build up of toxic metals in the outer reef 
tract area can be correlated with adjacent regions of maximum population and 
development. Carbon-12 enrichment in outer reef corals may indicate that sewage, 
which also carries toxic metals, is reaching the reef environment in the study area. It 
is considered that concentration of Pb and Hg in bottom sediments is reaching sufficient 
levels above background in certain areas of the Upper Keys to be of environmental 
concern. Such areas are those proximal to sewage outfalls (i.e. Tavernier Key) and in 
restricted basins (i.e. Pennekamp marina). Values are also high in bottom sediments for 
Cr, Co, and Zn, but little research has been done on the environmental impact of these 
metals. Therefore, predictions cannot be made for the study area ecosystem concerning 
the adverse effects of these metals. A previously indicated, toxic metals are more 
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