Biotoxicity of Liquid Crystals from Obsolete Laptop Computers

Liquid crystals (LCs) are organic molecules which are typically elongated and have a non-uniform distribution of the electrical charges in the molecule, resulting in a dipole. LCs are widely used in displays of computers and other electronic devices. The rapid obsolescence rate of electronics results in large amounts of liquid crystal display (LCDs) entering the environment. Merck Company (Germany) is the largest producer of LCs. According to the testing requirements for the notification of new chemical compounds of the European Union, Merck did some acute toxicity tests to their LC products. According to their results, only 8 LCs were classified as harmful among more than 200 LCs tested. In the bacteria mutagenicity test, only one out of 228 individual LCs showed mutagenic potential. However, these results cannot point out whether LCs have chronic toxicity at low concentrations. In reality, LCs are usually in very low concentrations in the environment. LCs contained in a LCD are typically 0.0006 g/cm. In this study, a low-concentration, longperiod exposure test was used to evaluate the chronic toxicity of LCs to animals. Catfish were used as the test animals and GSH (Glutathione), CAT (catalase), GPx (glutathione peroxidase), and SOD (superoxide dimutase) of the Antioxidant Defense System of the fish were used as biomarkers to investigate the early effects of the pollutants. The LCs were taken from obsolete laptop personal computers made in the early 1990s. The catfish were fed with food containing different contents of the LCs for 40 days, and then dissected. The activities of the four indicators in the livers were measured. The results show apparent responses of SOD and CAT activities to the LC contents or doses. The threshold of catfish livers from adaptation reaction to poisoning reaction was 4.5~9.0 μg/g-fish/d. GST activities did not show significant changes with the LC doses. It was concluded that LCs have chronic effects on fish at low concentrations and SOD and CAT are the most effective biomarkers to examine the LC biotoxicity to aquatic lives.