Nonoxidizing Molluscicides

 

Most of these chemicals were originally developed for bacterial disinfection and algae control in water treatment systems (Claudi and Mackie 1994). They include organic film-forming antifouling compounds, gill membrane toxins, and nonorganics. The proprietary formulations have a higher per-volume cost than oxidizing chemicals but remain cost-effective due to lower use rates and rapid toxicity. They often can provide better control of adult mussels due to the inability of mussels to detect them; because shells remain open, shorter exposures are required. Most are easy to apply and do not present corrosion problems for metal components. Although most compounds are biodegradable, detoxification or deactivation may be required to meet State and Federal discharge requirements; but there is virtually no formation of toxic by-products (McMahon, Shipman, and Long 1993).

 

Intermittent, periodic, or semicontinuous applications rather than continuous applications of nonoxidizing compounds for adult mussel control adds to their cost-effectiveness (Netherland 1997). Usually treatment is on a periodic basis for 24 hr or less during the warm-water season to remove newly settled mussels or adults, with two to three applications per year: early in the season, at peak veliger activity, and when evidence of settlement is first seen. If they are used in coordination with monitoring programs that provide accurate veliger and mussel settlement data, frequency of application can be minimized (Green 1995). Water temperature helps determine treatment concentration and length of exposure required (Claudi and Mackie 1994; Green 1995).

 

Within the nonoxidizing molluscicides there are several groups of compounds:

  1. Quaternary ammonium compounds, polyquaternary ammonium compounds, or . Quaternary ammonium compounds (QACs) are organic salts that have a wide variety of uses in industry. They have been used as coagulants and flocculants in potable water since the late 1960’s, and have American National Standards Institute/National Sanitation Foundation (ANSI/NSF) Standard 60 (1997) certification for this use. Several of these have been used for control of Asian clam (Corbicula fluminea). They are also effective in controlling mollusk fouling in once-through industrial cooling systems, and recently received Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)/USEPA registration for use as molluscicides in municipal water (Blanck, Mead, and Adams 1996). QACs are cationic surfactants, and it is their surface-binding activity that produces antifouling biocidal effects. Two major types of chloride-ion-containing QACs are used commercially in the molluscicides CLAM-TROL CT-1™ and MACROTROL™ 9210 and Calgon H-130M, and BULAB® 6002 contains a poly-QAC (polyquat) (EPRI 1993). QACs also adsorb strongly to sediments, clay particles, organic matter, and other negatively charged surfaces, so that water column concentrations are normally very low (EPRI 1993). Where QACs are released directly into a receiving system, they may require detoxification by adsorption onto bentonite clay or other agents, but are not harmful to aquatic organisms once they are bound to anionic substances (Dobbs et al. 1995).

  2. Aromatic hydrocarbons. Compounds such as BULAB® 6009 and MEXEL 432™ also have molluscicide properties due to their surfactant and anti-macrofouling activity.

  3. Endothall. This herbicidal compound, long used against aquatic nuisance plants, has been formulated as EVAC® and registered to control zebra mussel.

  4. Metals and their salts.
    1. Copper ions have long been known to be toxic to planktonic or microbial organisms in water, and yet not pose a threat to humans due to binding and inactivation in sediments. These properties are put to use in the deployment of copper ions via the MACROTECH system for zebra mussel control. Various copper and zinc ions are major components of antifouling coatings and chemicals (Race and Kelly 1997).

    2. Potassium, potash, and potassium chloride have flocculant activity that is able to precipitate various life stages of the zebra mussel out of water (Fisher et al. 1991).

 

Zebra Mussel Chemical Control Guide

Introduction