OBITUARY : Norman Aldridge

Norman Aldridge was regarded by his peers as one of the most thoughtful and influential toxicologists of our time.

He was fascinated by the interaction of chemicals with living organisms and driven by "the insatiable urge to make sense of things" which Sir Peter Medawar defined as the true basis of research. He loved research but also to apply the results to real life, and he encouraged his students, post-doctoral fellows and visiting scientists from around the world to do the same.

Toxicology is a multi- disciplinary science which draws on the skills of basic science in biology, chemistry, medicine and, more recently, molecular biology. Aldridge's interest and investigations spanned a wide range of areas but is illustrated by his work on a poisoning incident with malathion, a widely and safely used pesticide of the 1960s and 1970s.

When cheaper formulations of malathion began to appear in the late 1970s, about 2,500 malaria-control sprayers in Pakistan became ill and five died. As Director of the World Health Organisation (WHO) collaborating laboratory at the Medical Research Council (MRC) Toxicology Unit at Carshalton, Surrey, Aldridge developed a series of experiments that demonstrated that the enhanced toxicity of malathion was due to an impurity, isomalathion, generated by storage of some of the samples in hot, humid, uncontrolled conditions.

Typically Aldridge was not content to solve only the immediate problem. He believed that understanding how and why chemicals exert toxic effects was fundamental to risk management. He demonstrated that isomalathion inhibited enzymes that normally degrade the small amounts of malathion ingested through accident or during work. He then went on to show that there were other impurities that also potentiated the toxicity but that they also had an unusual effect on the lung. All this work led to changes in the manufacturing and storage procedures for malathion to prevent this occurring again.

It is a tribute to Aldridge's ability and unassuming personality that authorities from all over the world would turn to him for advice, even after his retirement. His involvement in unveiling the mechanism of toxicity caused by the chemical disasters of Bhopal, in India, and the toxic cooking oil in Spain was to develop an understanding to reduce the likelihood of a similar recurrence of such events.

Aldridge spent the Second World War years as a corporal laboratory technician at the Chemical Defence Establishment at Porton Down. Stimulated by Sir Charles Lovatt-Evans, John Barnes and others, he was drawn into toxicology and graduated (London, external) in Chemistry and Physiology via long and hard part-time study. Following the Second World War, the pros-pect of massive expansion of chemical and pharmaceutical industries led the MRC in 1946 to found a Toxicology Unit to "do something" about the possible hazards to which operators and users might be exposed.

Thus it was natural that, when John Barnes was appointed medical director of the Toxicology Unit, he should invite Aldridge to be the first scientific member of staff. He obtained his PhD in Biochemistry (London, external) for fundamental work on the mechanism of interaction of organo-phosphorous compounds with enzymes. This understanding of mechanism facilitated the development of useful pesticides from a class of compounds originally designed for chemical warfare.

By the time of his retirement in 1985, Aldridge had been head of the Biochemical Mechanisms Section of the Toxicology Unit for 20 years and Deputy Director for 10. He was Founder Chairman of the British Toxicology Society, Secretary-General of the International Union of Toxicology and was honoured with awards and academic appointments in Europe, Asia and America. He was also Editor-in-Chief of the Biochemical Journal during the 1960s. He was appointed OBE in 1977 for services to toxicology.

Throughout his "retirement" he continued as Visiting Professor of Biochemical Toxicology at Surrey University, where he had contributed extensively to the design and operation of MSc courses strong in the mechanistic approach to toxicology. He also continued editorial work for international journals and to advise the MRC and WHO on both research and health problems.

Norman Aldridge will be remembered as an amiable man who loved to get to the heart of an issue. The pursuit of mechanisms of toxicity is a rigorous scientific activity but also great fun, and led him to delve into unexplored areas of biochemistry and physiology. He could often be found with a group of all ages and nationalities where his probing questions stimulated discussion and further questions, whether they be of current political issues or scientific conundrums. He would seize data which did not fit hypotheses as trophies of research, ask questions and devise experiments to distinguish between alternative explanations. He never built an empire of research workers but influenced the world of toxicology through his students and visiting scientists and his (sometimes terrifying) trenchant challenges to presuppositions. "Why?" from Aldridge rocked many a person on to their back foot.

During his career he was a visiting scientist at the Universities of California and Wisconsin in the United States, and Trondheim, Norway. His book Mechanisms and Concepts in Toxicology, which was published shortly before his death, embodies his thoughtful, challenging multidisciplinary approach to his work.

Martin Johnson

Wilfred Norman Aldridge, toxicologist: born Nuneaton, Warwickshire 22 November 1919; Head, Biochemical Mechanisms Section, Medical Research Council 1966-85; OBE 1977; married 1946 Kathleen Chivers (one son, two daughters); died Winchester 30 June 1996.