Accumulated Heavy Metal Content in Wolf Spider, Pardosa astrigera (Araneae: Lycosidae), as a Bioindicator of Exposure

Abstract

To investigate the rate and extent of heavy metal accumulation in a potential indicator species of wolf spider, Pardosa astrigera (L. Koch) (Araneae: Lycosidae), adult spiders were exposed to three different heavy metals by dietary uptake. The spiders were regularly fed with heavy metal-coated fruit flies (20 mM CdCl 2, 10 mM PbCl 2, 10 mM HgCl 2; singly or altogether) up to 8 weeks, and the heavy metal contents in individual spiders were analyzed. Accumulation pattern of individual heavy metal in P. astrigera body was significantly different. Both Pb and Hg reached the accumulation saturation point (ca. 3-4 ug/spider) in a relatively short period of exposure (two weeks). In contrast, the Cd accumulation gradually increased up to 6 weeks and then arrived at the saturation point (ca. 10 μg/spider). These findings indicate that the spider is more selective in the Cd accumulation compared to Pb and Hg. Similar patterns of individual heavy metal accumulation were also observed in the exposure to complex heavy metals, where the accumulation capacity for Cd was most significant. The contents of Cd and Pb in the P. astrigera collected from the down-stream area of Sin-gil stream were ca. 1.2 and 1.6 μg/spider, lower than the saturation level, but well reflecting the heavy metal contamination status of the area. The Cd accumulation in P. astrigera was also confirmed by histo-chemical staining of Cd with QAI [2-(8-quinolylazo)-4, 5-diphenylimidazol], in which vacuole-like complexes containing Cd were intensely stained in the hepatopancreatic tissue of the 20 mM CdCl 2-exposed spider. No mortality was observed during the time course of heavy metal exposure but the development of P. astrigera both in nymphal and sub-adult stages was suppressed by the constant exposure to 20 mM CdCl 2 as judged by the reduced rate of body weight gain, suggestive of its apparent sub-lethal effects.