Question

In the first eight weeks of growth, each Chinese brake fern absorbs approximately 800 ppm of arsenic per week, where ppm = 1 mg of arsenic / 1 kg of plant. Assuming each brake fern weighs 0.5 kg, how many brake ferns must be planted (and harvested or disposed of after eight weeks) in order to remove 1 kg of arsenic from the contaminated soil? Round up to the nearest whole number for your answer. * 0.64

Answer 1

Given that in the first eight weeks of growth each chinese break fern absorbs approximately 800 ppm of arsenic per week per 1 kg of plant.

We have 1 ppm = 1 mg of arsenic / 1 kg of plant.

Then 800 ppm = 800 mg of arsenic

It is also given that each fern weight 0.5 kg then the mass of arsenic each fern can absorb per week is 0.5 x 800 mg = 400 mg of arsenic per week.

The growth period of plants is eight weeks.

If 400 mg of arsenic is absorbed in one week, then the mass of arsenic absorbed in eight weeks is

400 x 8 = 3200 mg = 3.2 grams (since 1 gram = 1000 mg)

Thus 3.2 grams of arsenic is absorbed 1 fern from soil in eight weeks

Then 1 kg or 1000 grams of arsenic will be absorbed by (1 kg = 1000 grams)

=1000/3.2 ferns = 312.5 ferns.

Thus 313 break ferns (rounded upto whole number) must be planted in order to remove 1 kg of arsenic from contaminated soil in eight weeks.