Pollution of the aquatic biosphere by arsenic and other elements in the Taupo volcanic zone : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biology at Massey University

Abstract

An introduction to the Taupo Volcanic Zone and probable sources of polluting elements entering the aquatic environment is followed by a description of collection and treatment of samples used in this study. The construction of a hydride generation apparatus for use with an atomic absorption spectrophotometer for the determination of arsenic and other hydride forming elements is described. Flame emission, flame atomic absorption and inductively coupled plasma emission spectroscopy (I.C.P.-E.S.) were used for the determination of other elements. Determinations of arsenic and other elements were made on some geothermal waters of the area. It was found that these waters contribute large (relative to background levels) amounts of arsenic, boron and alkali metals to the aquatic environment. Some terrestrial vegetation surrounding hot pools at Lake Rotokawa and the Champagne Pool at Waiotapu was found to have high arsenic concentrations. Arsenic determinations made on the waters of the Waikato River and some lakes of the Taupo Volcanic Zone revealed that water from the Waikato River between Lake Aratiatia and Whakamaru as well as Lakes Rotokawa, Rotomahana and Rotoehu was above the World Health Organisation limit for arsenic in drinking water (0.05 µg/mL) at the time of sampling. Arsenic accumulates in the sediments of the Waikato River and Lakes of the Taupo Volcanic Zone. The levels were variable, but characteristically around 100 µg/g. Trout taken from the Waikato River and some lakes in the Taupo Volcanic Zone, had flesh arsenic concentrations of the same order of magnitude as the water from which they were taken. Trout from Lakes Rotorua, Rotoiti and Rotomahana contained average flesh mercury concentrations above the World Health Organisations limit for mercury in foodstuffs (0.5 µg/g). There were positive correlations between weight, length and flesh mercury concentration. Freshwater mussels from Lakes Rotorua and Tarawera had arsenic concentrations above the World Health Organisations limit for arsenic in foodstuffs (2 µg/g). Shellfish taken from the mouth of the Waikato river and from Raglan were below the World Health Organisation's limit for arsenic and mercury. Aquatic macrophytes from the Waikato River had arsenic concentrations many times greater than the water from which they were taken. Some samples of Ceratophyllum demersum had arsenic concentrations above 1000 µg/g dry weight. Water cress from the Waikato River at Broadlands and Orakei Korako contained on average 400 µg/g and 30 µg/g arsenic respectively. An experiment was conducted on the uptake of arsenic by water cress. It was found that water cress does accumulate arsenic if placed in an arsenic solution.