Mycrocystin-LR is considered in the WHO Guidelines for Drinking-water Quality (GDWQ).

For individual chemicals, the GDWQ also consider:

Review of WHO guidance on cyanotoxins in water

As part of the "rolling revision" plan of work for the GDWQ, WHO is currently reviewing the health effects evidence base for cyanobacteria and their toxins (or "cyanotoxins") in water. This programme of work will review the existing provisional guideline value for microcystin-LR, and evaluate the best available evidence to determine if guideline values can be established for other harmful cyanotoxins, namely, cylindrospermopsin, saxitoxin and anatoxin. As part of this work, an assessment will be undertaken to determine if it is appropriate to establish shorter-term guideline values for these cyanotoxins.

It is expected that the updated risk assessments will be incorporated in the 2nd addendum to the 4th edition of the GDWQ, or the 5th edition, and a revised edition of the WHO publication Toxic cyanobacteria in water.

WHO’s current guidance on cyanotoxins in drinking-water can be found in the current edition of the GDWQ and includes a provisional guideline value of 1 µg/L for microcystin-LR (free plus cell-bound). The fact that this provisional guideline value is based on life-time exposure needs to be considered when identifying appropriate remedial action in the event of shorter-term exceedances above this value.