Live and let dye?


Concerns were recently raised at the Advanced Herbicide Training Workshop about the health hazards of spray marker dye. This is the dye that is used in herbicides to help with minimising over spraying, avoiding hitting good plants and seeing where you have missed. It was noted that dyes can be carcinogenic (cancer causing).

There are only two commercial spray marker dyes that are known carcinogens, Rhodamine B and Crystal Violet. Habitat Brisbane has in the past supplied Rhodamine B in a Nufarm product that also contains Diethylene glycol, ingestion of which has caused many deaths.

The main risk with Diethylene glycol is drinking it. There is no evidence of human toxicity from contact. The antidote to ingestion of Diethylene glycol is ethanol so if you had a high blood alcohol level (i.e., if you were extremely drunk) you would probably be less affected. Do not try this at home. Deaths from Diethylene glycol (related to toluene) occurred in suicide attempts, contamination of food products and occasions when ‘elixirs’ containing Diethylene glycol were drunk by religious or similar congregations – this occurred in Haiti.

Rhodamine B, which is the actual dye-stuff, is certainly carcinogenic and has been removed from cosmetic and food use. It is also most dangerous when ingested, but aerosol forms (spray-mist in the air) are also a risk by inhalation. Basically, if you can smell the herbicide while spraying, you are inhaling the herbicide AND the dye.

Inhalation while spraying with normal safety procedures has no proven harmful affects, but obviously in enclosed spaces mixing concentrated forms it could pose significant risks. Skin contact with Rhodamine B is not considered harmful but not much is known. Two current views exist on its possible risk. Firstly it might be harmless because it contacts dead skin and gets sloughed off. The second view is that because it stains the skin could become a repository for its penetration into the body.

Are any dyes safe?

The most common blue marker dyes for herbicide use are generally considered safe and are not listed as toxic under any local or international laws. Yet because they do not contain known toxins, manufacturers do not have to state actual chemicals. They usually say “proprietary non-hazardous chemical ingredients”.

The American DEA was really keen to find a safe dye for spraying to eradicate marijuana but in 1997 a detailed study found there were problems with all dyes and basically no literature on the topic.

Interestingly the UK forestry found that blue dyes reduced effectiveness of glyphosate when the herbicide was used at low doses or on resistant plants.

Generally it would seem that the advice to avoid dyes is generally good, especially when using a non-ionic surfactant. This sticky surfactant makes it more obvious where you have sprayed and it makes contact more obvious because of its very soapy feel.

Blue liquid dues would probably smell like vinegar and be basically acidic, because they are probably using the chemical known as Acid Blue 9 – Disodium Salt (Hidacid Azure Blue 65%). Strong acid has its own risks, and acid-based blue dyes might also be avoided on that basis.

The advantages of dye are obvious – reducing overspraying and accidental spraying into water or on plants you do not want affected. It also helps reduce contact exposure because it is so obvious. If you see dye on your clothes or skin you can wash it off straight away. The best advice is to follow the instructions about personal safety equipment, weather conditions, and handling. Wear gloves when handling and to avoid skin contact while spraying. Wear full covering clothes. It is relatively easy to develop the skills in spraying so you avoid inhalation, by not spraying upwind and adjusting the spray mist using a brass nozzle, and wearing a respirator.

Disposable respirators are usually for particulate matter and are not really very helpful against toxic aerosols. To be safe against inhalation you should wear a half mask respirator with filters that protect against organic vapours and odours.


North respirators and filters on Safetyquip – This is just a common, sample brand. We do not endorse any particular manufacturer.

Responsible Use of Herbicides and Pesticides – from the SA Government


Using dye markers to reduce pesticide use

Seeing Red (or Blue) – benefits of dye markers in spraying …

USA EPA data for Rhodamine B

Healthline 2007 on Diethylene glycol

Health Canada