Determination of Metals in Natural Waters, Sediments, and Soils

T. R. Crompton

• Publisher: Elsevier
• Year: 2015
• ISBN:
  9780128027004
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Determination of Metals in Natural Waters, Sediments and Soils provides analytic labs with a comprehensive overview of the various methods available for analysis of metals and serves as a manual to determine metal concentrations in different media such as natural waters, waste waters, sediments and soils. The book begins with a discussion of sampling techniques and preservation and then covers metals in rivers, surface ground and mineral waters and metals in aqueous precipitation. It concludes with detailed information on analysis of metals in sediments.

Determination of Metals in Natural Waters, Sediments and Soils provides a foundation for informed action by environmental interest groups and regulators and a starting point for further study by graduate students, professionals, and researchers.

• Includes all of the methods currently available to assess metals in water, sediments and soils
• Covers metals in surface ground and mineral waters
• Summarizes the strengths, weakness and precautions of different methods and provides a table summarizing the methods with reference citations

Chapter 1

Metals in Natural Water Samples

Sampling Techniques

Abstract

This chapter discusses a variety of devices used to sample various types of natural nonsaline waters, such as surface water, groundwater, rain, ice, and snow. The question of change in sample composition between sampling and analysis is discussed. Many reviews have appeared in the literature on techniques for the collection, preservation, storage, and prevention of contamination, and these are discussed in detail. Deep-water sampling is a special case, and specific techniques and special devices have been developed to provide reliable samples for analysis.

Keywords

Groundwater; Natural water; Sampling; Sediment; Soil; Surface water

Chapter Outline

1.1 Introduction 1

1.2 Sampling Devices 2

1.3 Filtration of Water Samples for Trace Metal Determination 5

References 7

1.1. Introduction

Heavy metals are among the most toxic and persistent pollutants in freshwater systems. Many research and monitoring efforts have been conducted to determine sources, transport, and fate of these metals in the aquatic environment. However, studies have shown that contamination artifacts have seriously compromised the reliability of many past and current analyses,¹ and in some cases, metals have been measured at 100 times true concentration.² These induced errors are of great concern, since artifact-free data are necessary to detect trends and to identify factors that control the transport and fate of toxic heavy metals. In addition, without accurate and reliable data, it is impossible to accurately monitor the effect of costly regulations aimed at reducing metal emissions. To avoid these problems, and to enhance the quality of trace metal data, laboratories are putting substantial effort into improving protocols for sample collection, handling, and analysis.³ This greater level of effort devoted to clean methods is costly in both money and time.

The problems caused by contamination when measuring trace metals were first brought to the attention of the scientific community by Patterson in his investigation of stable isotopes in the 1960 and 1970s.^4–6 Largely through his influence, clean methods became part of the standard operating procedures used by chemical oceanographers starting in the mid-1970s.^5,6 Freshwater chemists were slow to adopt these same techniques, with the notable exception of the long series of investigations on lead cycling by Patterson and co-workers.^7–11

With few exceptions,^12–15 limnologist have begun to use clean techniques only in the last 10 years. This was spurred, in part, by oceanographers who began to study freshwater systems such as the Mississippi River,^16–18 Great Lakes,¹⁹ and Amazon River.²⁰ The result of this activity has been to cast serious doubt on earlier routine measurements. Thus, Flegal and Coale²¹ have questioned surveys of lead in surface waters,^22,33 and Windom et al.² disputed the reliability of the United States Geological Survey (USGS) National Stream Quality Accounting Network. Ahlers et al.⁴ and Benoit²⁴ implied that most previously reported results may be in error because of failure to follow appropriate clean protocols. A parallel can be drawn with chemical oceanography, where virtually all uncensored (i.e., other than nondetects) trace metal data from before about 1975 are considered invalid.

Common to all analytical methods is the need for correct sampling. It is still the most critical stage with respect to risks to accuracy in aquatic trace metal chemistry, owing to the potential introduction of contamination. Systematic errors introduced here will make the whole analysis unreliable.

Surface-water samples are usually collected manually in pre-cleaned polyethylene bottles (from a rubber or plastic boat) from the sea, lakes, and rivers. Sample collection is performed in front of the bow of the boat, against the wind. In the sea or in larger inland lakes, a sufficient distance (about 500 m) in an appropriate wind direction has to be kept between the boat and the research vessel to avoid contamination. The collection of surface water samples from the vessel itself is impossible, considering the heavy metal contamination plume surrounding each ship. Surface-water samples are usually taken at 0.3 to 1 m depth, in order to be representative and to avoid interference by the air–water interfacial layer in which organics and consequently bound heavy metals accumulate. Usually, sample volumes between 0.5 and 2 L are collected. Substantially larger volumes could not be handled in a sufficiently contamination-free manner in the subsequent sample pre-treatment steps.

Reliable deep-water sampling is a special and demanding art. It usually has to be done from the research vessel. Special devices and techniques have been developed to provide reliable samples.

Samples for mercury analysis should preferably be taken in pre-cleaned glass flasks. If, as required for the other ecotoxic heavy metals, polyethylene flasks are commonly used for sampling, then an aliquot of the collected water sample for the mercury determination has to be transferred as soon as possible into a glass bottle, because mercury losses with time are to be expected in polyethylene bottles.

Luettich et al.²⁵ have described an instrument system for remote measurement of physical and chemical parameters in shallow water.

Martin et al.²⁶ compared surface grab and cross-sectionally integrated sampling and found that very similar concentrations of dissolved metals were obtained by these procedures.

Cox and McLeod²⁷ have discussed difficulties associated with preserving the integrity of chromium in water samples.

1.2. Sampling Devices

The job of the analyst begins with taking the sample. The choice of sampling gear can often determine the validity of the sample taken; if contamination is introduced in the sampling process itself, no amount of care in the analysis can save the results.

Sampling the subsurface waters present some not completely obvious problems. For example, the material from which the sampler is constructed must not add any metals or organic matter to the sample. To be completely safe, then, the sampler should be constructed either of glass or of metal. All-glass samplers have been used successfully at shallow depths; these samplers are generally not commercially available.^28,29 To avoid contamination from material in the surface film, these samplers are often designed to be closed while they are lowered through the surface, and then opened at the depth of sampling. The pressure differential limits the depth of sampling to the upper 100 m; below this depth, implosion of the sampler becomes a problem.

Implosion at greater depths can be prevented either by strengthening the container or by supplying pressure compensation. The first solution has been applied in the Blumer sample.³⁰ The glass container is actually a liner inside an aluminum pressure housing; the evacuated sampler is lowered to the required depth, where a rupture disc brakes, allowing the sampler to fill. Even with the aluminum pressure casing, however, the sampler cannot be used below a few 1000 m without damage to the glass liner.

Another approach to the construction of glass sampling containers involves equalization of pressure during the lowering of the sampler. Such a sampler has been described by Bertoni and Melchiorri-Santolini.³¹ Gas pressure is supplied by a standard diver’s gas cylinder, through an automatic delivery valve of the type used by scuba divers. When the sampler is opened to the water, the pressur...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Chapter 1. Metals in Natural Water Samples: Sampling Techniques
• Chapter 2. Water Sample Preservation
• Chapter 3. Metals in River Water
• Chapter 4. Metals in Surface, Ground, and Mineral Waters
• Chapter 5. Metals in Aqueous Precipitation
• Chapter 6. Analysis of Metals in Sediments: Sampling Procedures
• Chapter 7. Metals in Sediments
• Chapter 8. Determination of Metals in Soils
• Index