Aquatic Ecotoxicology

Volume 2: Fundamental Concepts and Methodologies

Alain Boudou

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351086769
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

Research into ecotoxicology can be classified into three fundamental concerns: abiotic factors, which characterize the physicochemistry of environments; biotic factors, relating to biological structures and functions; and contamination factors, which define the modes of pollution of ecosystems. The most significant research methodologies currently being developed in aquatic ecotoxicology are presented, specifically experimental approaches in the laboratory

In Situ Ecotoxicological Studies: Bases and Methodologies

Chapter 8

The Pollution of the Hydrosphere by Global Contaminants and Its Effects on Aquatic Ecosystems

François Ramade

TABLE OF CONTENTS

I. Introduction

II. Dispersion and Circulation Mechanisms of Contaminants in the Biosphere

• Atmospheric Transport of Pollutants
• Transfer of Pollutants from the Atmosphere into Water
• Uptake by Biota
  • Bioconcentration by Living Organisms
  • The Transfer and Concentration of Pollutants in Aquatic Trophic Chains and Food Webs in Natural Ecosystems

III. The Ecosystem Perspective in Aquatic Ecotoxicology

• Demoecological Effects
• Effects on Community Structure and Dynamic
  • Reduction in Population Size and Loss of Species
  • Reduction in Density and Species Richness, the Indicator Species
  • Species Diversity and the Use of Bioecological Indices
  • Effects of Pollutants on Frequency Distribution of Species within the Affected Communities
  • Biocenotic Methods for the Study of the Pollution Impact on Aquatic Ecosystems
  • Succession and Recovery
• Effects on Ecosystem Functioning
  • Effects on Biomass and Productivity
  • Effects on Secondary Productivity
  • Decomposition and Element Cycling

References

I. Introduction

Over 75,000 chemicals are in common use today, and several thousands of new compounds are added to this figure each year.^1,2 Fortunately, few categories among them are used in large amounts or are released unintentionally into the environment to such an extent that they really threaten the aquatic ecosystems on a wide scale or, worse, on a global one.

Presently, freshwater and brackish habitats as well as marine ecosystems are currently polluted by persistent organic compounds (organochlorine pesticides and polychlorinated biphenyls (PCBs) for example), oil slicks or chronic hydrocarbon release, and, to a smaller extent, by heavy metals and radioactive wastes. Furthermore, some atmospheric contaminants through the so-called acid rain phenomenon are impinging more and more severely on freshwater ecosystems of the whole Northern Hemisphere and even on some industrialized areas south of the equator.³ This phenomenon of acid precipitation has aroused deep concerns during the last decade for it has been spreading without disruption since the end of the 1950s.

As a consequence, not only the direct impact of this chemical pollution on the hydrosphere, but also its effect on the physical nature of the aquatic environment has to be assessed. Ultimately, even nontoxic contaminants can indirectly exert their ecotoxicological effects on aquatic ecosystems on a rather wide scale. The most documented example is the one of continental and coastal water dystrophication by organic matter from domestic and industrial origin discharged by sewage pipes.

The present extent of contamination by these various pollutants is a matter of serious concern. For example, over 3 million tons of dichlorodiphenyltrichloroethane (DDT) have been manufactured since its discovery in 1939, of which over 1 million tons had already been transferred to the oceanic ecosystem at the beginning of the of the last decade.⁴

Though figures for PCBs are known with less accuracy, it may be estimated that more than 1 million tons of these compounds are still in use all around the world. As a consequence of their widespread use in electrical devices such as plasticizers and additives of various chemical products, PCBs can presently be detected in the most remote area of the biosphere,⁵ i.e., in the benthic fishes Trematomidae living in the deep waters of the antarctic continental shelf.⁶

Among the other major aquatic contaminants must be listed the oil spills and other causes of hydrocarbon release, of which 4.5 million tons are expected to be discharged annually into continental waters and ultimately into the oceans of the world.

If we turn now to atmospheric pollution, it has been estimated that 200 million tons/year of sulfur dioxide was released into the atmosphere at the beginning of the present decade,⁸ a significant part of it appearing as the S0₄ anion in continental water bodies through the water cycle, causing their acidification.

II. Dispersion and Circulation Mechanisms of Contaminants in the Biosphere

The pollutants mentioned above and some others may be listed among the most serious types of contaminants that threaten aquatic ecosystems, for they are widespread, released in sufficient quantities and over a wide-enough area that significant pollution of large ecosystems and even of the whole biosphere, could result in the long run. Moreover, even point spills of sufficient duration and amount can be the origin of widespread environmental contamination.

The emission of pollutants into the environment is a complex phenomenon and cannot be limited to the deceptively fixed image of a waste pipe spilling out its effluents into a lake. In almost all cases, substances discharged into the environment are going to be carried a very long way from their source. Atmospheric and hydrological circulation systems will then disperse them progressively throughout the biosphere.

A. Atmospheric Transport of Pollutants

Many pollutants of aquatic ecosystems are not directly discharged into them, but are primarily from terrestrial origin or behave as secondary contaminants. As a consequence, atmospheric transport plays a fundamental role in the dispersion of pollutants and their distribution into different aquatic biotopes. Any organic or mineral compound, even if it is solid, can theoretically be carried by the air. For gases, entry into the atmosphere is direct; for liquids with a weak vapor pressure, it is in the form of aerosols; and for nonsublimable solids, it takes the form of fine particles. Even low-vapor-pressure compounds, such as various organic pesticides, can dissipate into the atmosphere through codistillation with water vapor.⁹

Some of the major contaminants released by man into the atmosphere are natural constituents of it. Sulfur dioxide, nitrogen dioxide, carbon dioxide, and even mercury add to the normal quantities present in the atmosphere which come from various biogeochemical processes and natural phenomena such as volcanism.

It has been possible to calculate the average retention time for microscopic nonsedimentable particles as being 1 week at 3000 m, 2 months at the tropopause level, 1 year in the lower stratosphere, and 2.5 years at an altitude of 340 km.¹⁰

B. Transfer of Pollutants from the Atmosphere into Water

Apart from a few rare exceptions, atmospheric pollutants do not remain in the air ad infinitum, but precipitation introduces them into the hydrosphere or indirectly via the runoff and the leaching of soils. Solid particles are carried mechanically or by dissolving; gaseous substances are dissolved in rainwater. Snowfalls which filter through the atmosphere are also a very efficient process for extracting contaminants from air and bringing them into continental water bodies and the sea.¹¹ The pollutants then circulate on the continental surface, trickling into the soils and contaminating groundwater. Processes of leaching and water erosion play an essential part in the transfer of pollutants to the hydrosphere. Finally, geochemical phenomena will eventually introduce the majority of man-made pollutants into the oceans of the world, which are the ultimate receptacles for toxic agents and other pollutants produced by technological civilization.

The fundamental role of the water cycle in the transfer of pollutants was proved by studies made of radioactive fallout following the A- and H-bomb tests in the 1950s.¹²

Various analytical studies have confirmed that the combined processes of atomospheric circulation and precipitation play a major role in the contamination of aquatic habitats and could transport pollutants a very long way from their point of emission. For example, in the most remote rural areas of Great Britain, rainfall averages 14 ppt of PCBs, which is a rather high concentration.¹³

Far worse, at the end of the 1960s it was even shown that the snow falling in the central region of the Antarctic continent is polluted by DDT and other organochlorine compounds!¹⁴ In areas of the world where the ocean is very far from industrialized countries, marine mammals are significantly contaminated by PCBs, DDT, and hexachlorocyclohexanes (HCHs).¹⁵ Analysis of the pH of rainwater indicates that the pH level has dropped seriously over Europe (Figure 1) as a result of the use of fossil fuels rich in sulfur.^{16 and 18} At the end of the 1970s, it was shown that the entire land mass of the Northern Hemisphere, as far north as 10° latitude was exposed to acid precipitation.¹⁹

Similarly, rainfall can play a major role in the contamination of oceanic waters by pollutan...

Table of contents

• Cover
• Title Page
• Copyright Page
• Foreword
• Preface
• Introduction
• The Editors
• Contributors
• Acknowledgments
• Table of Contents
• Freshwater Ecosystems: Ecological and Ecotoxicological Bases
• Analytical Chemistry and Chemical Assessment of Contaminants in Freshwater Ecosystems
• In Situ Ecotoxicological Studies: Bases and Methodologies
• Index