Zinc is a very common heavy metal. Zinc is also found in metal works and production
and is used in the pharmaceutical industry as an ingredient in sun block, deodorants,
athlete’s foot preparations and many other topical medications (EBI). Zinc gets into the
environment by mining, steel production, coal burning, and burning of other wastes. Zinc
compounds that are commonly found at hazardous waste sites are zinc chloride, zinc
sulfide, zinc oxide, and zinc sulfate. Most zinc is bound to soil and does not dissolve into
water, therefore it is important to test for this metal because it affects all things that live
in soil, eat plants that grow in soil and are generally exposed to soil on a regular basis.
Rainbow trout
Daphnia magna
Fathead
minnow
Blue gill
LC 50 Values
.63-3.0 mg/l
.35 mg/l
.64-3.0 mg/l
1.2 mg/l in a 96
hr test
Table 1.1 LC50 Values for local native species of fishes and invertebrates. LC50
ranges are dependant on water hardness. (PAN)
Our test species Panicum rigidulum is an excellent choice because this species is
an obligate wetland species. It is a tolerant species to acidic environments as it requires a
minimum pH of 5.0 which is excellent because metals have a tendency to oxidize.
The plant species Panicum rigidulum was collected from Radford Universities’ Wetland
which is located on campus near the Dedmon Center. This particular species of plant was
the best choice because it is found throughout the wetlands, which provided a lot of
samples needed from various sites that covered the entire wetland. A detailed map of the
wetland was used to give accurate collections. The samples that were taken came from
every other plot throughout the wetland. The twenty samples that were taken was placed
in Ziploc bags and marked with the plot from which they were extracted. For the future
chemical tests on the plant samples it was confirmed that the microwave digestion
machine could only hold ten samples at a time, so after reevaluating the map it was
decided upon to use every other, other plot. After washing each of the samples
thoroughly they were left out to dry for a week. The dried samples were then taken into a
chemistry lab and grinded up in to small pieces using a mortar and a pestle. Five grams of
each of the ten samples were placed vessels (designed for the microwave) with 10ml of
nitric acid. The vessels are deposited into a rotating turntable. The turntable was then
placed inside of the microwave on 180 +/- 5 degrees Celsius for approximately 9.5
minutes. The microwave rotates at 3 rpm. When the digestion is complete the vessels
were allowed to cool for 15 minutes to avoid dangerous explosions from high
temperatures and exothermic reactions occurring inside each vessel. Each vessel was
carefully uncapped and vented in a fume hood. The reactants were then placed into 10
volumetric flasks by using a funnel with filter paper on top of the funnel to collect debris,
and then the funnel paper was rinsed off into the funnels with deionized water. The flasks
and contents were diluted with hydrochloric acid. All ten flasks were then taken into
another lab room to be tested by the flame absorption device. This test gave specific
readings of zinc found in our samples.
Datafile:
1) Column A is the numbered samples
2) Column B is the Absorbance of Zinc measured in Panicum rigidulum by using
microwave-acid digestion.
3) Column C is the milligrams of Zn per Liter of Solution.
4) Column D is the total amount of solution that was used.
5) Column D is the total amount of plant used in the experiment (in Kilograms)
6) Column E is the parts per million of Zinc in the plant itself (mg/kg or ppm).
7) Columns H through J is a statistical analysis.
Column H is the mean absorbance. Column I is the concentration ??. Column J is
the percent precision.