TOXINS FROM BLUE-GREEN ALGAE: TOXICOLOGICAL ASSESSMENT OF MICROCYSTIN-LR AND A METHOD FOR ITS DETERMINATION IN WATER
Report No FR0359/2/DoE 3

Jan 1994

SUMMARY

PREFACE

Toxin production by blue-green algae has been recognised for many centuries, but in recent years there appears to have been an increase in the severity of blooms affecting waters used for potable supply and recreation. Microcystin-LR is one of the most toxic and commonly occurring of these toxins.

As no method existed for its analysis in water, the Foundation for Water Research (FWR) and the National Rivers Authority funded the development of an analytical method for microcystin-LR in water, during 1990-1991 (part of contract F-1001). This was reported to the funding bodies in October 1991, and its performance was assessed in a multi-laboratory testing exercise in April 1993. This performance testing was jointly funded by FWR and the Department of the Environment (DoE) (under the supervision of the Drinking Water Inspectorate) under a separate contract (P-001 (FWR); PECD 7/7/428 (DoE)). Other work has been completed, within this overall programme of research, on the fate of microcystin-LR in water treatment processes.

In order to obtain information on the comparative toxicity by various routes of exposure, and the toxicity to the foetus and adult following repeated dosing with microcystin-LR, FWR and DoE (under the supervision of the Drinking Water Inspectorate) placed a contract with WRc for a jointly funded programme of research in October 1991. This contract (PECD 7/7/399 (DoE); F-1001 (FWR)) required WRc to recommend suitable studies, choose and supervise capable sub-contractors, manage the work and draw appropriate conclusions.

SUMMARY

Blue-green algae can, under certain conditions, massively increase in numbers in some water bodies and may form visible surface blooms or scums. Toxic effects on animals ingesting significant quantities of blue-green algal cells, usually from such blooms, have been recognised for over a century and some of the toxins involved have been classified according to their mode of action e.g. hepatotoxins, neurotoxins. The great majority of the hepatotoxins are collectively referred to as microcystins, which are now known to be closely related cyclic heptapeptides. At sufficiently high levels these can cause severe liver damage in animals, and one of the most toxic and commonly occurring in the UK is microcystin-LR.

As blue-green algal blooms have occurred in raw water supply reservoirs, a risk assessment of potential exposure by ingestion via drinking water was needed. Data were required on toxicity and levels of exposure to allow this to be undertaken. As no suitable toxicity data existed it was necessary to carry out a programme of toxicity testing, and as studies using tissue culture could not provide adequate information it was essential to work with laboratory mice. In order to determine levels of microcystin-LR in water to provide data on levels of exposure, an analytical method had to be developed. This was reported some time ago (Report FR0224), but has since been performance tested in a multi-laboratory exercise and shown to provide a reliable means of quantifying low levels of this toxin in water. The method together with the performance testing data, produced in the format of the "Methods for the Examination of Water and Associated Materials" (commonly referred to as "Blue Book" format) forms the Appendix to this report.

The toxicity studies showed that:

• microcystin-LR is 30 to 100 times less toxic by oral ingestion compared to intra-peritoneal injection;
• even at very high doses which caused maternal toxicity, there were no signs of foetal malformations, and the no effect level for any form of developmental toxicity was 600 µg kg^-1 bodyweight per day, given on days 6-15 of pregnancy;
• the clear no effect level for liver toxicity after dosing for 13 weeks, was 40 µg kg^-1 bodyweight per day, and this is also the probable no effect level even for minor changes in bodyweight and blood chemistry. This would give a margin of safety of over 250 for a 5 kg bottle-fed infant drinking 0.75 litres per day of water containing 1µg l^-1 microcystin-LR.

It is recommended that seasonal variations in the levels of microcystin-LR in drinking water potentially affected by algal blooms should be measured, and that no further in vivo studies be undertaken until this assessment has been made. In vitro studies of the comparative sensitivity of human and mouse hepatocytes to microcystin-LR should be considered. It would also be advisable to conduct in vitro studies to contribute to the risk assessment of microcystin-LR as a tumour promoter if this is confirmed as a hazard.

Copies of the Report are available from FWR, price £25.00 less 20% to FWR Members _