In your own words, explain chemical mobility in soils, and how it is related to the chemical and the soil properties. Use an example from the slides to contrast a pesticide with high and low chemical mobility.

Chemistry by Geoffrey

Homework set 9 – Total points: 100

 

Instructions: Please type your answers to the following questions and submit an electronic copy of your completed assignment on Canvas. Points for each question are indicated in front of the question. Please name your file as CHEM151_HW6_FirstNameLastInitial

This homework set is on material covered Week 12-13, chemistry of sorption onto solid surfaces

 

Question 1

(5 pts) What is a functional group and how does it affect the sorption potential of chemicals? Describe using an example from Lab #10.

 

Question 2

(5pts) How are layer silicate clays different from metal hydroxides and soil organic matter? How does this difference affect their potential to sorb chemicals?

 

Question 3

(5pts) In your own words, explain chemical mobility in soils, and how it is related to the chemical and the soil properties. Use an example from the slides to contrast a pesticide with high and low chemical mobility.

 

Question 3

(5 pts) Describe the effect of pH on sorption. How does an increase in pH affect the charge of solid surfaces, like metal oxides and SOM? What is the impact of pH increase on cationic nutrient adsorption? Why is lime commonly used as a soil enhancement?

 

Question 4

(5 pts) Under what conditions is a linear isotherm a good assumption to quantify sorption capacity of a chemical on a solid surface? How is the Freundlich isotherm different from a linear isotherm?

 

Question 5

(5 pts) The values of logKoc for the insecticide lindane and the herbivide 2,4D are 2.87 and 1.54 respectively. For each pesticide, suppose rain water dissolves 12 ppb from the plants and surface soil and then carries it downward. If the soil has 2.3% organic carbon, calculate the equilibrium concentration of each pesticide in soil.

 

 

Question 6 (2+3*6 = 20 pts)

You are designing a water filter made of powdered seashells combined with dried mango peels. You want to quantify how much of chemical A you can remove via adsorption at equilibrium, and what the properties of this sustainable adsorbent are. In a beaker with 10 grams of your seashells/mango combo, you add 100 mL of water with a concentration of the chemical at 5 mg/L.

  1. What is the total mass of chemical Α in your system?
  2. You measure the concentration of chemical A after sorption has reached equilibrium and you find that it has been reduced from 5 mg/L down to 2.6 mg/L. Determine the mass of chemical A that has been removed from the water.
  3. Determine the mass of chemical A that has adsorbed onto the soil.
  4. Determine the concentration of chemical A in the soil in units mg/kg.
  5. The following graph gives the linear isotherm for chemical A. Determine the Kd. Derive the units of the Kd.

 

 

 

  1. Use a mass balance to show that the mass of chemical A before sorption is the same as the mass in the two phases after sorption.
  2. Would increasing the time you let your contaminated water sit with the filter increase sorption? What could you do to increase sorption?

 

 

Question 7 (2×5=10pts)

Consider the chemical P-dichlorobenzene. Consider a groundwater sample that has a concentration of P-dichlorobenzene of 0.2 ppb. The logKow for P-dichlorobenzene (Hanch et al., 1995) is 3.44. Find the Koc of P-dichlorobenzene.

  1. For a soil that has 1.6% organic carbon, determine the sorption coefficient Kd.
  2. For the above soil, calculate the concentration of P-dichlorobenzene at equilibrium in the soil in mg of P-dichlorobenzene per kg of soil (mg/kg)

 

 

 

 

 

 

 

 

 

Question 1 – Guest lecture on Contaminated Sediments Management by Dr. Cho (5×8=40 pts)

 

  • In a couple sentences, compare organic and inorganic compounds in terms of their ability to sorb onto soils and sediments. There are many differences; identify the one that pertains to sorption specifically.
  • What are the components of aquatic sediments? Where is it found in the environment?
  • What happens after a major storm event in relation to sediment?
  • Which components of aquatic sediments interact significantly with hydrophobic organic chemicals, why and via what mechanism?
  • What does in-situ sequestration mean in plain language? Explain what in-situ means, what sequestration of a contaminant means, and then what does in-situ sequestration mean for management of contaminants. Feel free to google it; answer in your own words.
  • Describe the hypothesis of the research presented by Dr. Cho. Refer to slide “Lessons from Nature”.
  • What makes activated carbon a very effective material for sorption?
  • Write five sentences to discuss the figure shown below from Cho et al., 2009. Things to include in a discussion of a figure are a) what the figure shows, description of axes b) what is the take-away message from the figure, description of the data and c) how it relates to the context of the text in which the discussion of the figure appears. Here, your context is this assignment.

 

 

 

 

 

 

 

 

 

 

[BONUS QUESTION] Read the feature article by Ghosh et al., 2011 and answer the following questions.

 

  • The article begins by saying that aquatic sediments are the “ultimate repositories” of past and ongoing discharges of pollutants. Explain in your own words why that is.
  • Why does sediment contamination pose a threat to fish, fish-eating wildlife and humans?
  • What is dredging and why is it not always a good solution to manage contaminated sediments? Identify four reasons why.
  • What is the proposed solution in this paper, and how does it affect the bioavailability of HOCs? How does this address the threat discussed in question 2 above?
  • To prove a concept or make an argument, scientists have to report evidence from the literature that their idea is actually viable, and then produce data that support their hypothesis. Treasure hunt: Find an example of evidence used in this feature article for AC-amended sediment reducing bioavailability of contaminants. Describe that evidence in your own words in two sentences.
  • True or false? Treatment of contaminated sediments with activated carbon amendment only works for hydrophobic organic contaminants. If yes, why? If no, what else does it work for?
  • The article states “the varied laboratory results demonstrate that the effectiveness of sorbent amendment on lowering contaminant bioavailability increases with decreasing AC particle size, increasing dose of AC, greater mixing, and contact time”. Explain in four sentences why you think these four design variables affect the effectiveness of sorbent amendment.
  • What makes a pilot study more difficult than a bench-scale study? Why is a pilot study important to test a hypothesis about environmental management?
  • The article provides five design considerations that increase confidence in the findings of a field pilot study. The concept of multiple lines of evidence is central to environmental risk assessment and management. Describe what it means in two sentences with an example.
  • True or false: sorbent amendment removes contaminants from sediment. Explain why or why not.