Answer to Question 1
The cost can be much lower because the majority of the cost of a cleanup is for
salaries of workers and for use of specialized equipment. As the quote suggests, disposal of
the waste material is also a big expense.
With phytoremediation, plants do most of the cleanup while costing little to nothing: plants
do not demand a living wage. Plants (or also possibly animals) concentrate certain waste
products in one place. The plants can be incinerated and the valuable materials concentrated
further and used again as a resource.
Answer to Question 2
The reverse is true: it is blue because it reflects blue and absorbs red and green
from the spectrum of sunlight.