Lead: Its Effects on Environment and Health

The series of Metal Ions in Life Sciences was started in 2006 and has since comprised 16 volumes on the role of metal ions in various areas of the biosciences in the broad range between bioinorganic chemistry and biomineralization on the one end, and metallomics and clinical chemistry on the other (I–XVI). This new series followed and complemented the 44 volumes (1–44) previously produced by several different publishers, but with the same “editor family”, in the years 1973-2005 under the frame Metal Ions in Biological Systems. Only few of the now 60 volumes (!) were dedicated to the role of a single element (volume 13: copper; 15: zinc; 17: calcium; 23+II: nickel; 24: aluminum; 26: magnesium; 31: vanadium; 34: mercury; 7+35: iron; 37: manganese; 39: molybdenum and tungsten; 40: lanthanides; XI: cadmium; XVI: alkali metals), and to this list a volume on lead (XVII) has now been added. This element showed up in previous volumes already where its various effects had to be considered in another context such as neurogenerative deseases (I, Chapter 14), toxicity of organometallics, as well as organometallics in the environment (VII, Chapter 5) and others. Volume XVII now provides a largely comprehensive and up-to-date account of the effects of lead on the environment and on the health of organisms. For this formidable task, the editors have invited a group of some 35 competent authors to review specific fields in altogether 16 chapters.

In a first account, the reader is introduced to the Bioinorganic Chemistry of Lead in the Context of Its Toxicity (by W. Maret), starting with some history and consequences of the manufacturing of lead-containing materials, and leading to current regulatory levels for water, air and food. The symptoms of lead poisoning are described indicating the target organs and the cellular and molecular actions therein. This is followed by Chapter 2 on Biogeochemistry of Lead, Its Release to the Environment and Chemical Speciation (by J. T. Cullen and J. McAlister). The abundance of lead in the continental crust (natural and anthropogenic sources) and its mobilization leading to the loads observed for the atmosphere, the ground and surface waters and the deposits are described. The development of lead pollution associated with the introduction and the final ban of leaded gasoline is illustrated and the relevant speciation and biogeochemical cycling are presented. In Chapter 3, P. C. Hauser covers the Analytical Methods for the Determination of Lead in the Environment, from sampling and speciation to spectrophotometry, XRF, AAS, MS, and electrochemistry. This is following by Chapter 4 on specific techniques for Lead Removal from Industrial Wastewater Using “Smart Capsules” (by B. Tylkowski and R. Jastrzab). These capsules made up of alginates or other scavengers, collect lead cations at pH 6 and release it at low pH. Lead Speciation in Microorganisms is the subject of Chapter 5 by T. J. Stewart, who summarizes techniques for the metal speciation and intracellular metal localization in bacteria, fungi, algae, and other species. Chapter 6 on Human Biomonitoring of Lead Exposure (by K. Klotz and T. Goën) turns to the control of the consequences of chronic exposure of humans to lead contaminations by ICP MS, AAS and other standard analytical methods. The effects of lead poisoning also lead to biomarkers for indirect assay.

Chapter 7 is dedicated to the Solid State Structures of Lead Complexes with Relevance for Biological Systems (by K. Aoki, K. Murayama and N.-H. Hu). This summary includes complexes with amino acids and peptides, nucleic acids and carbohydrates, the crystal structures of which may resemble the accommodation of lead cations in biological matrices. Among other aspects, the focus is on the hemi- and holodirectional effects originating from the 6s² lone pair of lead(II). Chapter 8 on Lead(II) Complexes of Amino Acids, Peptides, and Other Related Ligands of Biological Interest (by E. Farkas and P. Buglyó) complements the previous chapter by presenting the corresponding solution characteristics. The stability constants that characterize the homo- and heteroleptic complexation of lead cations by bioligands and their dependence on the pH of the aqueous solutions are discussed. Chapter 9 (by D. L. Wong, M. E. Merrifield-MacRae and M. J. Stillman) covers Lead(II) Binding in Metallothioneins which is most relevant for cysteine-rich (i.e. sulfur-rich) proteins. In these systems, lead(II) competes with a variety of other metals and the relative affinities govern the binding preference. A rich set of analytical tools allows a reliable speciation. Chapter 10 (by V. Cangelosi, L. Ruckthong and V. L. Pecoraro) introduces the results on Lead(II) Binding in Natural and Artificial Proteins both in the solid and solution state. Key models are glutathione, calmodulin and metalloregulatory proteins like the lead resistance operon pbr. Various model proteins have been designed to study the mode of lead binding and its consequences for structure and performance of the proteins. Chapter 11 (by A. Sigel, B. P. Operschall and H. Sigel) on Complex Formation of Lead(II) with Nucleotides and Their Constituents compares the mode of action of lead(II) on the title compounds with that of other metals and the corresponding interdependence. The definition and value of a “stability ruler” are discussed and the influence of pH and other parameters on the relative stabilities is screened. Main objects of the review are hydrocarbons, nucleobases and nucleotides in all their diversity, making the chapter one of the richest of the book. In Chapter 12 (by J. Palou-Mir, M. Barceló-Oliver and R. K. O. Sigel), The Role of Lead(II) in Nucleic Acids is presented. The main topics are lead(II) binding in tRNA, RNase P and the HIV-1 dimerization initiation site. In this context, lead(II) has been used as a hydrolytic cleavage agent to probe the binding of other divalent metals, with a particular emphasis on the substitution of calcium and strontium and on the “leadzyme” construct and its use in following cleavage mechanisms.

Chapter 13 (by H. R. Pohl, S. Z. Ingber and H. G. Abadia) has the title Historical View on Lead: Guidelines and Regulations. It is an introduction into the development of early and current legislative moves to protect humans and the environment from lead poisoning and pollution. This includes guidelines and regulations for occupational standards and for air, water and soil. The standards still differ in various parts of the world, but approach similar levels for areas like food and consumer products such as children’s toys. This chapter is thus an extension of Chapter 1, which also touched on these issues more generally. Chapter 14 (by M. Filella and J. Bonet) with the title Environmental Impact of Alkyl Lead(IV) Derivatives: Perspectives after Their Phase-out illustrates the environmental situation after the ban of tetraethyl- and tetramethyllead as gasoline anti-knock additives in the 1970s. In the decades between 1930 and 1990 in the USA alone 5.4 million tons of lead had been used in gasoline and ended up in the environment. Tetraalkyllead usage is now limited to piston-engine aircraft aviation and to car racing. The lead presently contained in environmental compartments thus largely originates from the pre-ban decades and is steadily decreasing. In air, water and soil (assisted by irradiation), the lead tetraalkyls are subject to rapid degradation to inorganic lead compounds. The lead traces in ice layers in Greenland, and in the arctic mosses, reflect the dramatic increase and decrease of pollution experienced during the period of almost a century, between 1920 and 2010, i.e. the beginning and end of the leaded gasoline. This leads directly to Chapter 15 on Lead Toxicity in Plants by H. Küpper. Major toxicity effects have been noted in a reduced photosynthesis, which is mainly due to the light-independent reactions leading to carbon dioxide fixation. Clear effects of genotoxicity and mitosis are less well documented and often refer to very high, environmentally irrelevant lead concentrations. It appears that plants are often very robust towards lead poisoning. Finally, Chapter 16 turns to Toxicology of Lead and its Damage to Mammalian Organisms (by S. Caito, A. C. B. Almeido Lopes, M. M. B. Paoliello, and M. Aschner). The authors describe the absorption, distribution and excretion of lead in mammalian organisms, which then show effects of neuro-, immuno-, hemato-, nephro-, and osteotoxicity. There is also a reproductive toxicity for males and females, which has been documented for humans since antiquity.

The book closes with a 20-page Subject Index, and most chapters have glossars of Abbreviations and Definitions.

In summary, the book presents a comprehensive review of the present knowledge of the role of lead in humans, flora and fauna, and the environment. It is well organized and well written. Information has been put together at a time when fortunately the threat of lead poisoning is greatly diminished as this metal has gradually been removed from many technologies, from plumbing, soldering, gasoline, glasses, paints, pigments, and materials to consumer goods. There is even hope that the appearance of electric automobiles will finally make the heavy lead-acid batteries redundant, which are leading by far in the demand for lead in industry. Interestingly, however, there is presently a movement towards perovskite solar cells that often are based on lead(II) compounds of the type RNH₂^, PbX₃^-, and which could mean a new increase in large-scale lead production. Hopefully, there may be other ways to harvest solar energy. The reviewer missed points like this in one or the other of the outlooks closing the chapters or the book.