Mytilus trossulus hsp70 as a biomarker for arsenic exposure in the marine environment: Laboratory and real-world results

Abstract

The highly conserved heat shock protein 70 (hsp70) is induced by heat and chemical toxins, particularly heavy metals such as arsenic (As). The use of Mytilus trossulus (bay mussel) hsp70 as a ‘screening’ biomarker for marine heavy metals contamination was assessed. Some studies have found high hsp70 sensitivity to heavy metals, while others have found the opposite. Few studies have realistically used low heavy metals exposures, and fewer have used real-world contamination exposures. Clean sub-tidal mussels from the Puget Sound, Washington State (WA), USA, were acclimatized for 2 weeks and exposed for 24 h to As-spiked seawater (n=9) or to contaminated seawater from an arsenical pesticide plant in Tacoma, WA (n=10) followed by a Western blot for hsp70. Hsp70 inductions were insignificant at 10 µg l⁻¹ As^III, but were strong at 100 µg l⁻¹ (p<0.05) and 1000 µg l⁻¹ (p<0.01), with the induction threshold estimated at 30–50 µg l⁻¹ As^III. Hsp70 induction roughly correlated with arsenical toxicity, with As^III>As^V>(CH₃)₂As^V. Altogether, the inter-individual variability of hsp70 levels tends to mask inductions at low As concentrations, making it a crude toxicity biomarker. In addressing this problem, the following options could prove promising: (1) pre- or post-stressing specimens for greater hsp70 sensitivity, (2) use of internal protein controls such as actin, (3) use of hsp70-reporter gene constructs, and (4) detection with hsp60, heme oxygenase-1, metallothionein, CYP450, MXR or GPx.

Keywords: :

• Heat shock protein (hsp) 70
• arsenic
• arsenite
• arsenate
• mussels
• Mytilus trossulus

Acknowledgements

The study was supported by the Summer Environment Research Award from the University of Chicago Environmental Studies Program, chaired by Professor Theodore L. Steck. Additional support came from Professor David Archer, University of Chicago; and Professor Paul Strieleman, Howard Hughes Foundation, University of Chicago. The author thanks Professor Michael LaBarbera, University of Chicago; Dr Eric Crecelius, Battelle Marine Sciences Laboratory; Professor Gretchen Hofmann, UC Santa Barbara; Dr Christine Rivera and Chip McCauslin, Varian Instruments; Dan Alvarez, CEM Instruments; and Stan Palmquist, Severn Trent Laboratories, for their advice and support.