2.2.2 LARVAL ASSAYS
H. iris and E. chloroticus larvae were raised for 72 h in 300 ml FSW in glass jars placed in a flowing seawater bath to maintain a near constant temperature. Water temperature was 16°C ±1 in all E. chloroticus assays and 14°C ±1 in all H. iris assays. Embryos were placed in culture jars before 1st cell division, no more than 1 h after fertilisation. Embryo density was 30/ml for E. chloroticus (ASTM 2012) and 1/ml for H. iris (Anderson et al. 1994), and was confirmed to be suitable for these species in previous pilot experiments. All glassware was washed with hot water, soaked in 10% hydrochloric acid for a minimum of 4 h, rinsed and soaked in distilled water for 12 h, and rinsed in FSW before use. Two experiments were conducted: one with single metals (Cu, Zn and Pb) and one with combined metals (Cu + Zn, Cu + Pn and Zn + Pb). The single metal experiment had two runs for both species and the combined metal experiment a single run. Metal concentrations are shown in Table 2.1. They were based on a range-finding pilot trial, and the current experiments were designed to have one concentration producing no toxic effect, one producing close to 100% abnormal larvae, and two concentrations producing intermediate effects as required for accurate estimation of EC50s (US EPA 2002a). The concentration range was adjusted between the two runs of single metal tests on H. iris to add more intermediate effects and reduce EC50s confidence intervals. Each metal level and control had three replicates, plus an additional replicate jar in control conditions (FSW) and one in the highest metal level for each metal, in which to monitor pH and temperature.