Slide 1

Analysis of Heavy Metals in Remediated Soil Using an Atomic Absorption Spectrometer (AAS) Introduction

Anthony Ng, Welch Summer Scholar Program

An Atomic Absorption Spectrometer (AAS)

University of Texas at Austin 2003

What are heavy metals?

Dr. J. J. Lagowski, Christine Johnson Welch Summer Scholar Program

Heavy metals are metallic elements that have a density greater than 6 g/cm3 and that can be hazardous at elevated concentrations. Some heavy metals such as antimony are suspected human carcinogens. Others such Cadmium, Chromium, and Copper can accumulate in the kidney and liver and cause severe damage to those systems. A heavy metal whose symptoms on humans are infamous is lead. Damage to the nervous system is common, and metal retardation and death may result.

Abstract Elevated levels of heavy metals in soil can be hazardous to the environment and toxic in human consumption. In order to be able to identify and quantify these metals, a method called acid digestion must be utilized to break down the soil structures and free the heavy metals. This method is designed to simulate prolonged acid rain exposure to the soil. It involves the controlled addition of nitric acid and hydrogen peroxide to several remediated soil samples. After the heavy metals are freed, the samples are finally analyzed for hazardous levels that are set by the Environmental Protection Agency (EPA) using an Atomic Absorption Spectrometer (AAS).

Light Source

AAnalyst 700

How does an AAS work? •Basic components of an AAS: ¾Light source ¾Sample cell used to produce gaseous atoms (Flame aspiration) ¾Optical system used to detect how much light is actually absorbed

Calibration Curve

Testing for heavy metals: Must use a method called acid digestion followed by analysis using an instrument called an atomic absorption spectrometer (AAS).

Flame Aspiration

Sample Preparation Procedure for acid digestion: ™Weigh out samples ™Add aliquots of nitric acid, heating after each addition ™Add D.I. water and hydrogen peroxide once brown fumes no longer appear after adding the nitric acid ™Continue to add hydrogen peroxide until bubbling dies down to a minimum ™Filter out solid particles ™Dilute the filtered solution

A calibration curve is made by running a standard through the AAS and is essential to a successful test run on a sample. It acts as a standard for comparison for the data received from the samples. With it, we can find out the concentrations of the heavy metals in the sample.

Results

Optical System and Detector

(all results in ppb, nr = not readable)

Lot/El emen t 147

As

Cd

Pb

Ag

Ba

Cr

Se

Hg

0.159

nr

nr

0.257

2.213

1.976

nr

nr

148

0.113

0.073

nr

0.157

2.012

1.343

nr

nr

149

0.089

5.83

3.262

0.126

2.069

1.148

nr

nr

150

0.102

0.034

nr

4.795

1.987

1.556

nr

nr

151

0.019

0.42

nr

0.159

2.658

1.811

nr

nr

152

0.036

0.369

nr

0.113

2.668

0.012

nr

nr

153

0.02

0.038

nr

0.089

1.598

0.011

nr

nr

154

nr

0.006

nr

0.107

1.887

0.041

nr

nr

155

nr

0.005

nr

0.059

2.998

0.01

nr

nr

156

nr

0.285

nr

0.036

2.654

0.159

nr

nr

Conclusion: All results fell under the EPA regulations, and no hazards to humans are present in these samples. It is important to note that this experiment is only a small test along with many other test in determining the effectiveness and safety of the sample.