Polyelectrolyte flocculants in freshwater and marine water
Toxicant default guideline values for protecting aquatic ecosystems
Extracted from Section 8.3.7 ‘Detailed descriptions of chemicals’ of the ANZECC & ARMCANZ (2000) guidelines.
The default guideline values (previously known as ‘trigger values’) and associated information in this technical brief should be used in accordance with the detailed guidance provided in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality.
Description of chemical
Polyelectrolyte flocculants provide cost-effective means to improve recovery of mineral ores and remove suspended material from wastewater. They are intentionally added to wastewater at levels between 10 and 100 mg/L and can be used for sludge conditioning at much higher levels (Cary et al. 1987). However, these levels can be higher than those which cause acute effects on fish and there have been reports of unreacted polyelectrolyte flocculants causing fish kills in treated mining effluent in New South Wales (Lamberton 1995).
Chemical and physical properties
Polyelectrolyte flocculants, otherwise called organic polymeric flocculants (OPF), provide an alternative to conventional treatment with iron and aluminium salts. They are high molecular weight synthetic polymers, which can be formulated for specific applications. OPFs are characterised by a number of features (Lamberton 1995):
- chemistry of the polymer
- polarity (cationic, anionic, non-ionic or amphoteric)
- molecular weight
- charge density
- physical form (solid, aqueous solution, emulsion, etc.).
In Australia, most chemical groups of polymers are polyacrylamides, polydadmacs and epichlorohydrin-amine polymers (Bolto 1994). One of the major difficulties in controlling flocculant releases is that it is difficult to analyse for flocculant levels in water.
Despite their being in use for up to 30 years, there are few public and peer-reviewed data on the toxicity of OPFs. Toxicity varies with charge type and flocculant chemistry and acute toxicity ranged from 10 to 70,000 µg/L for cladocerans and between 100 and 1,000,000 µg/L for fish (Biesinger et al. 1976, Beim & Beim 1994). Generally, cationic flocculants have been found to be most toxic to fish but this varies for crustaceans.
Flocculants appear to act mainly by acute toxicity, probably by physical blocking and mucous production of gill tissue and sorption to small invertebrates (Biesinger et al. 1976, Cary et al. 1987, Beim & Beim 1994).
Toxicity to Australian and New Zealand species
Lamberton (1995) has studied acute effects of several OPFs to the eastern rainbowfish, Melanotaenia duboulayi, and the cladoceran, Ceriodaphnia dubia. This work has not yet been peer reviewed and can not be used for deriving guideline figures. Tentative results for 96-hour EC50 to fish of four cationic OPFs varied from 1300 to 5200 µg/L but anionic OPFs did not show any toxicity at > 110 mg/L. For C. dubia, the 48-hour EC50s varied from 90 to 190 µg/L for anionic OPFs to 220 to 790 µg/L for cationic OPFs.
Factors affecting toxicity of organic polymeric flocculants
Toxicity of OPFs is significantly reduced at high levels of organic carbon and total suspended solids (Biesinger et al. 1976, Cary et al. 1987, Goodrich et al. 1991, Hamilton et al. 1994). Water hardness and salinity may also affect their toxicity.
There were insufficient data to develop guideline trigger values for OPFs, particularly given the range of polymer types. As acute effects are reported as low as 10 µg/L, polymer concentrations greater than 1 µg/L may cause environmental harm.
As concentrations of OPFs can not usually be measured in water, discharges are best controlled by best management practices and other appropriate source control.
ANZECC & ARMCANZ 2000. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand, Canberra.
Cary GA, McMahon JA & Kuc WJ 1987. The effect of suspended solids and naturally occurring dissolved organics in reducing the acute toxicities of cationic polyelectrolytes to aquatic organisms. Environmental Toxicology and Chemistry 6, 469-474.
Beim AA & Beim AM 1994. Comparative ecological — toxicological data on determination of maximum permissible concentrations (MPC) for several flocculants. Environmental Technology 15, 195–198.
Biesinger KE, Lemke AE, Smith WE & Tyo RM 1976. Comparative toxicity of polyelectrolytes to selected aquatic animals. Journal of the Water Pollution Control Federation 48, 183-187.
Bolto BA 1994. Polymeric flocculants in water purification. Water 21, 431-435.
Goodrich MS, Dulak LH, Friedman MA & Lech JJ 1991. Acute and long-term toxicity of water-soluble cationic polymers to rainbow trout (Oncorhynchus mykiss) and the modification of toxicity by humic acid. Environmental Toxicology and Chemistry 10, 509-515.
Hamilton MA, Reinert KH & Freeman MB 1994. Aquatic risk assessment of polymers. Environmental Science and Technology 28, 187-192.
Lamberton C 1995. Acute toxicity and management of polyelectrolyte flocculants in Australian aquatic ecosystems. MSc thesis (Environmental Toxicology), University of Technology, Sydney.