The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. In the 1980s symptoms of what seemed at first to be a strange skin disease began to appear in the rural areas of Bangladesh and West Bengal (India). The numbers were small but by the 1990s there was a flood of cases of hyperpigmentation (dark spots), and also small hardened lumps (keratoses) on hands and feet, which were often disabling, as a result of proneness to fungal infections, and occasionally they became malignant. An epidemiological link was eventually made to water consumption because these symptoms were similar to those of arsenic poisoning in Taiwan, with its associated 'blackfoot disease'. The laboratory testing of Bengali patients' hair confirmed the diagnosis of arsenicosis and there is no longer any doubt that a major problem exists. By analogy with Taiwan, consumption of arseniccontaminated water in Bangladesh over periods of 5-20 years will lead to cancers of the lung, bladder and kidney; hypertension; cardiovascular disease; and peripheral vascular disease, which is characterised by black skin discolouration, ulceration and possibly dry gangrene (WHO, 2001; IPCS, 2001; Chen and Ahsan, 2004).Gradually, very gradually in the 1990s, it dawned on the Bangladeshi authorities that they had discovered perhaps 'the largest mass poisoning of a population in history' ( The present paper contemplates the meanings of irony in an environmental context, concentrating on one, that of indeterminacy. This is used to show that there is very little by way of a stable understanding of the 'crisis' that has been identified so confidently in the media. First, we show that spatial and depth variabilities in arsenic content are extraordinary at the local scale, making analysis, interpolation and prediction highly problematic. Then we revisit the vexed issue of safety standards. The threshold of the level of arsenic that is safe to consume is by no means straightforward and shifting from the Bangladesh standard to that of the World Health Organization (WHO) nearly doubles the population estimated to be 'at risk'. Third, we turn to the issue of measurement and find that the field testing kits (FTKs), at least in the way they are used, do not provide a sufficiently accurate and reliable foundation for the dataset upon which much of the debate about arsenic in Bangladesh is based. This undermines the scientific credibility of some of the remedial measures taken so far in the field. Next the paper investigates the nature of lay and expert knowledges of arsenic. These are in a nascent state, with...