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Poly N-isopropylacrylamide and N-isopropylacrylamide / N-tert-butylacrylamide copolymer nanoparticles of 50 to 70 nm were prepared by free radical polymerisation. The particle sizes of the copolymer nanoparticles were measured in the test media Milli-Q water, Algae Media, Daphnia Media and Microtox Diluent as a function of temperature. Whereas in Milli-Q water the particle size was seen to decrease above the lower critical solution temperature of the thermoresponsive polymer, in the test media it was seen to increase significantly, indicative of aggregation. At the temperatures employed for the ecotoxicological studies all particles, with the exception of the 50:50 copolymer existed as nanoparticles, however. The zeta potential of Poly N-isopropylacrylamide and N-isopropylacrylamide / N-tert-butylacrylamide copolymer particles measured in the different media was seen to correlate well with the ratio of N-tert-butylacrylamide monomer and therefore the hydrophobicity of the particles. Ecotoxicological studies of the copolymer nanoparticles was performed using four test species Vibrio fischeri, Pseudokirchneriella subcapitata, Daphnia magna, Thamnocephalus platyurus and the cytotoxicity of the 100% Poly N-isopropylacrylamide and 85:15 N-isopropylacrylamide / N-tert-butylacrylamide copolymer nanoparticles was evaluated using a salmonid cell line. Although no significant cytotoxicological response was recorded, significant ecotoxicological response was observed at particle concentrations of up to 1000 mg l-1. The ecotoxicological response was seen to correlate well with the ratio of N-tert-butylacrylamide monomer and therefore with the zeta potential of the nanoparticles. The toxic response in Daphnia Magna was seen to further correlate with the reduction in zeta potential pointing towards a contribution of secondary effects due to modification of the medium. No correlation with particle size was observed. The sensitivity of the test species was seen to vary depending on co-polymer composition. The relevance of the derived structure activity relationships is discussed.

The term ecotoxicology, first defined by René Truhart in 1969, essentially describes the study of the harmful effects of chemicals upon ecosystems and understanding the pathways by which these deleterious effects are elicited (Walker et al., 1996). Thousands of new chemicals are produced each year requiring ecotoxicological evaluation, in addition to existing chemicals for which limited or no ecotoxicity data exists. Increased public concern regarding the impact of these anthropogenic chemicals on the environment, prompted DIT to expand its research portfolio to include the niche research area of aquatic ecotoxicology. DIT’s Radiation Science Centre was officially renamed the Radiation and Environmental Science Centre (RESC) in 2000 to reflect the increasing incorporation of ecotoxicological research conducted at the centre.