Methods for measuring mercury in gas ebullition from fiber banks : A literature study

Abstract: Mercury contamination is an environmental issue with high priority due to its high toxicity. In addition to the atmospheric deposition, several lakes and rivers in Sweden are contaminated as a result from wood and pulp-fiber industries which stretches back 200 years. In Luleå, Sweden, a former groundwood industry, Karlshäll, has contributed to mercury pollution in the sediments of Notviken, a small bay connected to Luleå River and the Bothnian Sea, through release of process water. Industrial release of chemicals and wood pulp have resulted in a special type of sediment called fiber banks. The fiber banks contain high levels of organic matter and very little oxygen which contributes to large gas emissions from the fiber banks, gas ebullition. There is no generally accepted method for examining how mercury contaminants are spread through gas ebullition. The aim of this thesis was to review and find methods for that purpose. Through the literature review several types of methods emerged. Some of them were useful for measuring volumes of gas, whereas others were better designed for collecting gas and analysing it for concentration of elements. There are pros and cons with all methods but the one considered most useful in the case of Karlshäll would be Skarp’s method with active and passive sampling. The passive part includes setting up tents over the fiber bank with a known area, and then calculate the volumes of gas which migrate up through the water during a certain amount of time. The active sampling consists of stirring the fiber bank sediment with a stick and then gather the ascending gas bubbles in a Teflon-bag. The Teflon bag is thereafter sent to a chemical environmental laboratory for analysis of the concentration of elements. This method is the only one of the ones reviewed in this thesis which have been tested in Sweden at sites with gas- ebullition facilitated mercury transport. Although, Varadharajan et al’s (2011) sampling device with automation could be applicable if a long-term, high frequency monitoring programme would be used at Karlshäll. In addition, a sampling device with an integrated carbon-absorption-tube collector for trapping gaseous Hg would be beneficial if the samples can’t handle a long-distance transportation. Thus, the samples could be sent to a local laboratory instead. However, this type of device is not yet invented and would need further studies to develop.