Chloro- and bromoacetates in natural archives of firn from Antarctica

A firn core was drilled in Dronning Maud Land, Antarctica, to investigate t he presence of haloacetates in snow that had accumulated over the past 200 years. By employing GC-MS detection of methyl esters of haloacetic acids, w e were able to measure haloacetate concentrations down to one or a few nano grams per liter. Trichloroacetate (TCA) and dibromoacetate (DBA) were found in firn at concentrations that clearly exceeded the blank level of the app lied analytical procedure, with mean concentrations estimated to 12 and 6 n g/L, respectively. There were also indications that mono- and dichloroaceta te (MCA and DCA) were present in firn, whereas monobromoacetate (MBA) was f ound only in samples of surficial snow. We concluded that there is a signif icant natural background level of TCA and DBA in precipitation based on the following: (i) several of samples represented snow accumulated in the 19th century; (ii) haloacetates can be expected to be immobile in Antarctic fir n;(iii) extensive measures were taken to prevent sample contamination; and (iv) blank levels of the analytical procedure used were low and stable. In addition, our results suggested that MCA and DCA also occur naturally in pr ecipitation.