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The term "additives" is used to describe products that are either water-applied or land-applied in order to perform some water treatment purpose. Additives can come in a variety of chemical formulations including, but not limited to: chemical salts, polymers, acids and bases, and organic chemicals. Examples of additives include: biocides, boiler or cooling tower treatments, corrosion inhibitors, industrial process polymers, pH control, scale control, settling flocculent logs, soil stabilizers, erosion control products, and stormwater and wastewater clarifying agents.

Why are we concerned about additive use?

Products like those described above may cause undesirable impacts if they are discharged directly to the environment. In order to protect fish and other aquatic life in areas where discharges to surface water may be occurring, it may be necessary to review scientific information for these products and place limits in permits or other control documents.

An additive review is needed if:

  • the additive may enter a surface water without receiving treatment; or
  • the additive is used in a treatment process, but is not expected to be removed by treatment and may contribute to effluent toxicity.

What does an additive review entail?

During an additive review, secondary acute and secondary chronic values for the product are calculated. A secondary value is the highest concentration of a substance that can be discharged without causing toxicity to aquatic organisms (s. NR 105.03, Wis. Adm. Code). Secondary values are based on available toxicity data and account for uncertainty by using a safety factor. Once calculated, secondary values can be used to derive site-specific permit limits that are protective of fish and other aquatic life.

What information is needed for an additive review?

Section NR 106.10, Wis. Adm. Code, requires permittees to obtain written approval from the department prior to use of an additive. The permittee must submit dosage information, safety data sheets and toxicological data, as requested by the DNR for each additive for which approval is sought.

The following product information is needed for an additive review to be performed:

  • Product trade name and manufacturer;
  • Product chemical name (if available);
  • Product active ingredients including CAS numbers of product components (if available); and
  • Proposed application rate.

The following toxicity information is needed for an additive review to be performed.

Toxicity Text Results*

  • Lethal Concentration (LC50) or Effective Concentration (EC50) for a freshwater species**

Toxicity Test Parameters***

  • Test duration and endpoint
  • Test method used
  • Exposure formal
  • Control response

* Toxicity testing must be conducted on the whole product, including all active ingredients and all carriers, buffering agents, binding agents, etc. Toxicity data for only active ingredient(s) are not acceptable.

** At a minimum, one acute toxicity test result from a daphnid species (e.g., Daphnia magna, Daphnia pulex, Ceriodaphnia dubia) is required for an additive review to be completed.

*** The toxicity test parameters are needed for each species for which there is a test result.

The toxicity test method used, exposure format and control response are important pieces of information for department staff to have when determining the reliability of toxicity data used to calculate secondary values. Where toxicity data is provided on SDS sheets, this supplemental information is not usually provided, but it should not be difficult for the party who performed the test to provide it upon request.

Important points

Toxicity testing must be conducted on the whole product.

At least one acute test result from a daphnid is needed to do an additive review.

The additive review worksheet [DOCX] can be used by permittees to compile the information needed for a review. A fillable PDF version of the additive review worksheet is also available. 

The secondary value calculator [XLTM] was created to assist the DNR when calculating secondary values. Instructions for how to use this spreadsheet can be found in the step-by-step instructions for the secondary value calculator [PDF].

Do I need to submit acute and chronic toxicity data?

All additive reviews include the calculation of an acute secondary value. When discharge events or additive use occurs continually for 96 hours or more in a seven-day (168-hour) period, it may also be necessary to evaluate chronic secondary values. The limit calculation procedure using secondary values allows dilution from the receiving water when calculating chronic limits (NR 106.06(4)(b)) but not in the calculation of acute limits (NR 106.06(3)(b)). So in waters with a large amount of available dilution, acute limits may be much more restrictive than chronic limits. In these cases, chronic secondary values may be irrelevant.

Chronic secondary values can be calculated from acute toxicity data; however, this is done using a mathematical formula based on certain assumptions. Providing chronic toxicity data may allow for the calculation of a more representative chronic value.

More detailed guidance

The guidance document linked below describes the procedures for deriving secondary values for an additive, which are the concentrations in surface water that protect aquatic life from adverse short-term and long-term effects. Because the procedures for determining secondary values are the same regardless of the purpose of the additive, this document applies to both water-applied and land-applied additives. Department staff convert the secondary value to an allowable usage rate depending on the intended application.

Applicable administrative rules

Other resources

Contact information

For questions about specific wastewater applications, contact your local DNR representative: Wastewater staff

For additives program information, contact: