To the Editor: In their brief review of water and public health, Leder et al1 uncritically attributed the Palm Island “epidemic” of 19792 to algal toxicity, commenting that it was the only recorded manifestation of this phenomenon in Australia. The original report described a hepatitis-like illness (associated in many with dehydration and bloody diarrhoea) in 138 children and 10 adults of Aboriginal and Torres Strait Islander descent living on Great Palm Island, northeast of Townsville, Queensland.2 No causative agent was actually identified.

My investigation in the early 1980s of Toxocara pteropodis, a parasite of flying foxes, excluded it as a likely aetiological agent in the Palm Island outbreak, and compelled a critical reanalysis of other possibilities, which led me to conclude that subacute copper toxicity was the most plausible explanation. My rationale was published as a hypothesis.3 Sadly, discretion (to protect local technicians) compelled me to withhold critical information that explained how the community had been inadvertently exposed to excessive levels of copper in its water supply. Now that water management is becoming a major societal concern and algal blooms seem to be increasing in frequency, the issue needs to be resolved — and sufficient time may have elapsed for details to be revealed without impugning individuals.

In 1985, having concluded that copper poisoning was the most likely explanation, I contacted the environmental health personnel who had overseen the mixing of algicide into the Palm Island water supply in 1979. They were aware that the actual volume of water to be treated had probably been grossly overestimated, because Solomon Dam’s water level was very low at the time. This meant that an excessive dose of copper sulfate was added to the dam, but it was assumed that this would be “erring on the safe side”. Further, the copper sulfate was not distributed uniformly through the water in the dam: a local resident with a dinghy had been contracted and instructed to spread the bags of copper salt around the dam, but had instead dumped it all at one place — immediately over the outlet pipe which carried the island’s drinking water.

This would readily explain how the community encountered a sustained pulse of high copper levels in its tap water. While chronic copper poisoning can lead to infantile hepatic cirrhosis,4 acute gastrointestinal symptoms (as manifested during the Palm Island episode) are also well documented.5,6

In the absence of laboratory confirmation of copper toxicity, the cause of the “Palm Island mystery disease” must remain speculative. However, in any future similar outbreaks, copper poisoning should be excluded before attributing the cause to algal toxicity.