In this experiment students applied advanced instrumental methods of metals analysis to investigate the imprint of anthropogenic activities as observed in aquatic sediments. Sediments from a mid-latitude varved meromictic lake were collected using a cold finger corer and were sectioned by year; the core covered the time frame 1300 to the present. Metals were extracted by microwave digestion and analyzed by ICP-AES and GFAAS. Quality control spike and recovery, replicate, and blank analyses were all within acceptable limits. Target metal concentrations remained relatively constant until the late 19th century, when lead, manganese, and cadmium increased significantly. The concentrations of these metals then undergo a marked reduction toward the end of the 20th century, indicating a possible change in anthropogenic behavior.

The aqueous solubilities and octanol±water partition coef®cients (K OW ) of the benzoylphenylurea (BPU) insecticides te¯ubenzuron, chlor¯uazuron,¯ufenoxuron and hexa¯umuron were determined in comparison with the more extensively studied di¯ubenzuron. Both te¯ubenzuron and hexa¯umuron were substantially less water-soluble (9.4 (AE 0.3) mg litre À1 and 16.2 (AE 0.5) mg litre À1 in water, respectively) than the value previously reported for di¯ubenzuron (89 (AE 4) mg litre À1 in water). Log K OW values for di¯ubenzuron, te¯ubenzuron, hexa¯umuron,¯ufenoxuron and chlor¯uazuron were 3.8, 5.4, 5.4, 6.2 and 6.6, respectively, as determined using reverse-phase HPLC. Photodegradation of hexa¯umuron, te¯ubenzuron and di¯ubenzuron in water indicated hexa¯umuron to be the most rapidly degraded of the three compounds at pH 7.0 (t 1/2 =8.6 (AE 0.4) h) and pH 9.0 (t 1/2 = 5 (AE 1) h); di¯ubenzuron was the slowest of the three pesticides to degrade in pH 7.0 (17 (AE 4) h) and pH 9.0 (8 (AE 2) h) buffered water. In a solar simulator using river water buffered to pH 9.0, te¯ubenzuron, hexa¯umuron and di¯ubenzuron half-lives were 20 (AE 4), 15 (AE 2) and 12 (AE 1) h, respectively; dark controls showed no loss of parent BPU over similar time periods.

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