Analytical procedure
For each sample, between 0.3 and 0.5 g of tissue (wet weight) was weighed and placed in a Teflon digestion vessel with 7 mL of concentrated (65%) nitric acid (HNO3) and 1 mL 30% hydrogen peroxide (H2O2). The sample in the vessel containing concentrated nitric acid was then subjected to a microwave programme as follows: step 1: 25–200 C for 10 min at 1000 W and step 2: 200 C for 10 min at 1000 W. Digests were finally made up with deionised water to 25 mL in acid-washed
standard flasks. ICP-MS operating conditions: nebulizer gas flow 0.91 L min)1, radio frequency (RF) 1200 W, Lens voltage 1.6 V, cool gas 13.0 L min)1, auxiliary gas 0.70 L min)1. Instrument detection limits on the ICPMS were 2000 ppt for iodine.