Stay safe while preparing tank mixes. If in doubt, don’t mix: find out more first

When mixing products containing hazardous substances - at work, on your land, at home, or anywhere else – you need to know what you are doing.

June 2018

Not all products can be mixed safely, and some may need to be combined in a particular way. 

Some chemical products are designed for use when mixed with other chemicals, making a ‘tank mix’. Tank mixes are used in many places around New Zealand: you may be creating and spraying tank mixes at work, on your farm, lifestyle block or section, or in an urban garden.

Mixing chemicals may seem like an easy thing to do, but there can be unexpected consequences which may make the mixture dangerous or inadvisable to use. This guide gives you information to help you work safely, to protect you and the environment.

Note: this guide is not intended for large-scale manufacturers, who combine chemical products to package and sell as a branded product.

What you need to know Plus

‘Tried-and-tested’, industry-standard tank mixes, following the manufacturers’ instructions for creating them, can enhance the effectiveness of the mixture, meaning you can spray less or reduce the need for repeat sprays.   

However, mixing chemical products that are not designed to be mixed can have unexpected consequences, as can mixing standard combinations in the wrong proportions or in the wrong order of mixing.

You need to know what you are doing when working with tank mixes. Otherwise, you may end up with a mix that:

  • is more toxic to you, other people or the environment than the stand-alone ingredients, or is unsafe to use
  • is not as effective as the individual components
  • may affect the consistency of the liquid, so that you won’t be able to spray it
  • refuses to stay mixed.

We at the EPA are particularly concerned about your safety, and ensuring that other people and the environment are not exposed to the unforeseen effects of chemical mixes.

How do I know if these products are safe to mix and use? Plus

If a product is designed for use in a tank mix, it will sometimes say so on the label or packaging. The label may suggest other compatible products that can be mixed together, for example, when a herbicide is safe to mix with an insecticide to manage two types of pest at the same time.

The label may also advise on products that should not be mixed together, or should not be mixed with other products at all. Information about mixing the product safely may also be included on the products’ safety data sheets (SDSs).

Note: even if there isn’t information about mixing with other products or chemicals on the label, packaging or on the SDS, it doesn’t necessarily mean that the product is safe to mix.

The main aim is to work safely, to ensure the products are compatible and can be mixed safely. So if the information isn’t available on the product labelling and SDSs, we recommend that you do some research first before mixing and spraying. Ask your supplier, or the product importer or manufacturer, as they should hold more information about safe use of products, and which are known to be compatible. Rural suppliers often have in-house consultants who can advise.

Any use of products containing hazardous chemicals must meet the restrictions (or ‘controls’) that were put in place when they were approved for use in New Zealand. For tank mixes, you will need to consider the controls for all of the products in the mix – noting that these individual controls may be inadequate to manage any unforeseen consequences of the combination of chemicals in your tank mix.

To find out the controls for an approved product or ingredient in the EPA's Controls database

Supplying chemical mixtures to others Plus

If you have created a mixture and intend to supply it to others, make sure you are complying with the law. You must ensure that mixes made for supply are already approved for supply and use in New Zealand under the Hazardous Substances and New Organisms Act (HSNO) Act 1996. This applies whether you are mixing on a large or a small scale, regardless of whether you will be charging or giving the mixture away.

Approvals under the HSNO Act ensure that the benefits and risks of a substances are assessed, and controls are agreed for their use. In workplaces, you also have a duty to ensure, so far as is reasonably practicable, that your mixture creates no risk to the health and safety of the people you are supplying it to (under section 42 of the Health and Safety at Work Act 2015).

To find out more, please contact us (our contact details are below), or talk with WorkSafe New Zealand. Some tank mixes are already approved under the HSNO Act and we can advise you about these.

We at the EPA are also responsible for assessing applications for approvals for new hazardous substances in New Zealand, including new mixtures.

If you would like to seek an approval for a new mixture, or for more information about this process, see the ‘Making an Application’ page on our website 

To read the Hazardous Substances and New Organisms Act (HSNO) 1996

Read section 42 of the Health and Safety at Work Act 2015 for the workplace rules about safety during supply

Disposing of tank mix contents Plus

When planning the disposal of any hazardous substance, including tank mixes, you must follow the rules and stay within New Zealand law. Your mix must be disposed of in a manner that is required for all of the products that created the mix, erring on the side of caution if disposing of a custom tank mix whose hazardous properties are not fully understood. 

If creating tank mixes is a part of your business, you may already have an appropriate disposal facility. Alternatively, you could find a disposal company that specialises in hazardous waste.

Landfill sites across New Zealand have strict rules about what they can and cannot accept at their site. Check with your local landfill to find out whether they are able to accept your waste. The waste that landfills accept are controlled by consents from their regional council, so the regional council may also be able to advise on a suitable site.

Never dump tank mixes containing hazardous substances straight into the sewer or storm-water drain. Check with your local wastewater treatment plant about the types of trade waste that they can receive. Wastewater discharge consents are also controlled by the regional councils.  

See the EPA Hazardous Substances (Disposal) Notice 2017 for more about the rules for disposing of hzardous substances

Any questions? Please contact us Plus

Please email the Hazardous Substances Compliance team

Contact our call centre: 0800 2255 372 (0800 CALL EPA)

Contact WorkSafe New Zealand