Dictionary of Environmentally Important Chemicals

David C. Ayres, Desmond G. Hellier

• Publisher: Routledge
• Year: 2022
• Print ISBN: 9780751402568
• eBook ISBN: 9781351455442
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

A quick reference for information on chemicals of environmental importance, this dictionary has been carefully compiled and designed to make it useful for students. About 600 substances are covered in alphabetically arranged entries: these include some 70 pesticides. Entries vary in detail depending on individual aspects, but in general they include: composition/structure; physical propertied; sources; environmentally relevant reactions and pathways; detection; and toxic effects and regulatory limits. Many entries include short case histories. Immediately relevant sources are quoted for individual entries and a bibliography of principle publications and texts for further reading is included.

CADMIUM CAS No. 7440-43-9

Cd

Cadmium, a member of Group 12 of the Periodic Table, has an atomic number of 48, an atomic weight of 112.40, a specific gravity of 8.65 at 20°, a melting point of 320.9° and, a boiling point of 767°. It is a soft, ductile, silver-white metal, with eight naturally occurring isotopes, ¹⁰⁶Cd (1.25%), ¹⁰⁸Cd (0.89%), ¹¹⁰Cd (12.49%),¹¹¹Cd (12.80%), ¹¹²Cd (24.13%), ¹¹³Cd (radioactive, 12.22%), ¹¹⁴Cd (28.73%) and ¹¹⁶Cd (7.49%). Like the other Group 12 members (Zn, Hg), cadmium exists in a stable oxidation state of +2.

In the earth’s crust the cadmium level is ∼ 0.20 ppm (0.1 mg kg⁻¹) but varies widely according to type of rock. Cadmium, 67th in relative abundance, is obtained as a byproduct in the extraction of zinc from zinc blende, ZnS. Metallic cadmium is obtained by reducing the oxide with carbon. Sulphide ore roasting, coal burning, phosphate fertilizers (2–20 ppm) and sewage sludge (up to 22 ppm Cd) are the main sources of cadmium in the environment, leading to local and regional pollution of soils and river sediments. Average soil concentration ∼ 2 ppm. High levels of cadmium were found in spoil from former zinc mines at Shipham, Somerset, UK. In solution, cadmium is highly toxic to plants and animals. Despite being phytotoxic, some plant species accumulate cadmium, particularly leafy plants – lettuce, spinach, turnips greens – the average cadmium content of cigarettes is reported to be ∼ 2 μg⁻¹ Normal cadmium levels in plants are below 0.5 mg kg⁻¹ (dry weight). Cd is present in drinking water at ppb levels (0.01–0.15 μgl⁻¹). Further, since the concentration of cadmium in air is usually low (ngm⁻³), ingestion is the main way cadmium enters the human food chain. Only about 6% of the estimated 40–50 μg day⁻¹ of ingested cadmium is absorbed by the body, whereas 25–50% of the 2–10 μg day⁻¹ of cadmium in inhaled dust is absorbed. The average daily diet is 25–60 μg (WHO recommends that the daily intake of cadmium should not exceed 1 μg kg⁻¹ of body weight). The average body burden is 15–30 mg cadmium, stored in the liver and kidneys, where it is predominantly bound to metallothioneins, which are cysteine-rich proteins. In whole blood, cadmium is mainly bound to erythrocytes. Typical concentrations are blood serum 0.012 μg % and urine 0.06 μg %. Elimination from the body is slow and the biological half life is of the order of 10–20 years.

Uses. Cadmium and its compounds are used in the manufacture of batteries, pigments/paints, polymer stabilizers, alloys, printing and graphics, electroplated goods and safety rods in the nuclear industry. Cadmium is used in the production of special alloys melting at low temperatures. Wood’s alloy (50% Bi, 25% Pb, 12.5% Cd, 12.5% Sn) melts at 70° and is used in fuses for telephone installations and fire prevention systems. Babbit metals (Cd-Ag or Cd-Ag-Cu) are used in producing special antifriction bearings. CdS is an important yellow pigment and CdS and CdSe are semiconductors. Cadmium tungstate, X-ray screen production. CdO, ceramic glaze. CdBr₂ and CdCl₂ are used in photocopying.

In the EC, USA and other countries a number of directives have been issued to reduce or eliminate the use of cadmium, e.g. replacement of cadmium in electroplating by zinc, cadmium pigments by other metals/organics and cadmium-containing stabilizers in plastics by Pb, Ba, Zn or Ca/Zn. Recycling programmes for spent Ni-Cd batteries have been started by several battery manufacturers in some countries, e.g. France and Japan. Recent UK directives include the following: the cadmium content in manufactured material not to exceed 0.01% by weight; for incineration of waste and a plant capacity of 1–31 h⁻¹, the cadmium concentration should be less than 0.2 mgm⁻³.

Cadmium and its compounds are highly toxic and usually carcinogenic and have been designated as one of the 100 most hazardous substances. Very toxic by ingestion and inhalation. Acute ingestion of cadmium concentrations ≳0.1–1.0 mg kg⁻¹ day⁻¹produces symptoms of nausea, vomiting, abdominal cramps and headache. Inhalation may cause acute or chronic lung/renal diseases. Chemical pneumonitis or pulmonary oedema may result from acute over-exposure to cadmium fumes, as oxide and chloride aerosols, at a dose of 5 mgm⁻³ over an 8 h period. 1 mgm⁻³ inhaled over the same time period gives rise to clinically evident symptoms in sensitive individuals. Deaths from acute cadmium poisoning have resulted from inhalation of cadmiun oxide smokes and fumes, usually from welding operations on cadmium-plated steels in poorly ventilated areas. Lethal doses of cadmium have been calculated to be 2600–2900 mgm⁻³min⁻¹. Chronic poisoning: long-term exposure to cadmium may affect body organs and systems, especially the kidneys. Long-term inhalation of cadmium fumes resulted in chronic rhinitis and pharyngitis and nasal bleeding. Increased risk of lung and prostate cancer. Toxic effects are largely due to its ability to inhibit various enzymes systems by blocking the carboxyl, amine and especially sulphydryl groups in protein molecules. Cadmium reduces the activity of the digestive enzymes trypsin and pepsin. Affects carbohydrate metabolism and inhibits glycogen synthesis in the liver. Competition between cadmium an...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Glossary of acronyms and abbreviations
• Introduction
• Acetaldehyde
• Barium
• Cadmium
• Deltamethrin
• Endosulfan
• Fenitrothion
• Gadolinium
• Hafnium
• Imazalil
• Ketones
• Lanthanum
• Magnesium
• Naphthylamines
• Osmium
• Palladium
• Radium
• Samarium
• Tabun
• Uranium
• Vanadium
• Warfarin
• Xenon
• Ytterbium
• Zinc
• Appendix A
• Further reading