TOXICITY TO THE GRAIN WEEVIL OF SOME ALKYL COMPOUNDS APPLIED AS VAPOURS

Abstract

A simple fumigation technique is described, which allows twenty to thirty tests to be made at once with different concentrations of vapour. The 50% lethal doses (LD 50's) of different substances were estimated by the probit method of analysis, the slopes of the probit lines also being recorded.The present work had two aims, the first being the investigation of the relationship of the molar LD 50's of different substances to one another. The substances were so chosen that comparison could be made both within homologous series and, for compounds with the same alkyl groups, between them. The second aim was to find out to what extent the slopes of probit lines varied for compounds believed to have like and unlike modes of action.Some of the series were known to contain substances with an anaesthetic or narcotic effect, symptoms which are frequently attributed to substances with some type of physical action. Other series included compounds which had little or no observed narcotic effect, which were lethal at low vapour concentrations and for which evidence exists that they possess chemical toxicity for some organisms. A series which might reasonably be expected to have some of the attributes of both the ‘physical’ and chemical toxicants was also used.On plotting log molar LD 50's against the number of alkyl carbon atoms, the well‐known linear relationship was noted for the series with an observed narcotic effect, the constant logarithmic difference being large in all except the alcohol series. However, the upper members of the series which were presumed chemically toxic also possessed toxicities which showed a constant logarithmic difference, but a much smaller one than that characteristic of the first group. The bromide series had for its higher members a constant difference in the log LD 50's intermediate between these two groups. On the other hand, the lower members of the bromide, iodide and thiocyanate series had log LD 50's which were not related in any obvious way. These experimental results are discussed in terms of phase distribution and chemical reactivity.Two poisons whose modes of action on a given organism are much alike often show parallel probit regression lines, especially if they possess similar chemical constitutions. There is, however, no reason why this should necessarily be the case, and in the present investigation it was found that compounds with an observed anaesthetic or narcotic effect often had very different probit slopes. Within most series, the slope was not greatly different except for the lower and higher members, for which it often appeared higher than for the intermediate ones. Between series, a rough correlation often existed between probit slope and median response vapour pressure.