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I would like to comment on your excellent article on depleted uranium in Iraq (19 April, p 4) . Depleted uranium emits about 40 per cent less alpha particles than natural uranium, due to the removal of most of the uranium-235 and, more importantly, the uranium-234. Immediately after its production, that is the whole story. …

Your article on the use of depleted uranium used in shells in Iraq implies that this route into the environment is unique. However, we have been dispersing natural uranium into the environment for decades via our coal-fired power stations. Uranium, like most heavy metals, is present in coal at concentrations of a few parts per …

The implications of the discovery of genetic "no-go" zones between the chromosomes of proto-humans and proto-chimps might indeed be "huge" (19 April, p 15) . But they are not huge enough to justify the conclusion that geographic separation was not involved in bringing about the striking differences between the two species. They certainly do not …

Perhaps Joe Griffin is referring to another form of depression than the one I and many others know well, in which you dream less, not more (12 April, p 44) . In fact, most depressed people do not dream at all. If Griffin does not believe me, he should read Darkness Visible by William Styron. …

Griffin's revelations would come as a bit of a yawn to practitioners of cognitive behaviour therapy (CBT) or neurolinguistic programming (NLP). Albert Ellis, the father of CBT, has been teaching rumination interruptions since at least the mid-1970s. NLP has been offering the therapeutic use of metaphor and storytelling since the mid-1970s, when its originators modelled …

Your article on the Columbia space shuttle disaster attracted a letter from David Harris of the Aluminium Federation regarding the supposed non-flammability of aluminium (19 April, p 24) . He states authoritatively: "Your article raises the spectre of aluminium burning. This is a mythhellip;I have never seen aluminium burning in any formhellip;and nor do I …

Harris correctly states that aluminium would have melted in the Columbia disaster. But it is not impossible for aluminium to burn as he claims. Steel wool can be ignited with a match, but there is no flame. A flame is a region of reacting gases, for which the combustible has to vaporise. Magnesium and aluminium …

• The article on potential SARS treatments (26 April, p 6) stated that last year AVI Biopharma developed an antisense therapy in just two weeks to protect penguins at a Milwaukee zoo against West Nile virus, but that it had not been needed. In fact, the company has since told us that three penguins suffering …

Philip Walton's letter maintains that the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) is the "authoritative source" of information on radiation-related mortality and disorders (22 March, p 30) . But does the status of "UN scientific committee"really..confer a passport to uncritical acceptance? UNSCEAR figures are in fact frequently questionable. For instance, the …