Advice of the Office for Risk Assessment & Research on cyanotoxines in surface water for agricultural use

Establish a system for monitoring cyanotoxins in surface water for agricultural use, comparable to that for bathing water. In that system employ the guideline values calculated by BuRO as reference value for agricultural use of surface water. Do this in close consultation with the ministries of Health, Welfare and Sport and Infrastructure and Water Management. Ensure that this advice is published on the internet site of central government, drought dossier. These are the advices from the Office for Risk Assessment & Research (BuRO) to the minister of Agriculture, Nature and Food Quality (LNV).

Blue-green algae in surface water

Cyanobacteria (blue-green algae) can grow explosively in water during warm periods. Water contaminated with blue-green algae can present a health risk for humans and animals. For instance if the water is used for irrigation of food crops or as drinking water for cattle (drenching).

Reason for investigation

In 2006 BuRO derived a maximum total cyanotoxin concentration of 1 μg/L for spray irrigation of food crops and 40 μg/L for drenching of livestock.

In 2018, on the basis of a literature study, BuRO confirmed that the conclusions from the advice issued in 2006 were still relevant and current.

In 2019, the French Agence Nationale de sécurité sanitaire de l’alimentation, de l’environnement et du travail (ANSES) published new health-based guidance values for two cyanotoxins: cylindrospermopsin (CYN) and microcystine-LR (MC-LR). For MC-LR a much lower health-based guidance value was derived compared to the previous health-based guidance value. This led BuRO to evaluate and if necessary update its previous BuRO advice.

Research questions

BuRO has sought answers to two questions:

  • What is the maximum concentration of cyanotoxins in surface water at which no food safety risk occurs if food crops are spray irrigated with the water and subsequently consumed?
  • What is the maximum concentration of cyanotoxins in surface water that can be used for drenching of livestock, at which no food safety risk occurs through consumption of animal products?

NB: This research and advice is focused on food safety risks that can occur due to agricultural use of surface water contaminated with cyanotoxins. BuRO has not looked at the risks for swimmers or animal health risks when pets and animals drink this water.

Answer to questions

The following answers emerged from the research:

  • For (spray) irrigation of crops, the current recommendation value (1 μg/L) offers sufficient protection. This value is based on MC-LR, the most commonly occurring cyanotoxin in Dutch surface water.
  • For dairy cattle, 45 μg MC-LR/L is a safe value, for beef cattle 5 μg MC-LR/L. Due to a lack of data, no calculation could be made for the other cyanotoxins.