Influence of salinity on the actions of pentachlorophenol in haliotis as measured by in vivo 31P NMR spectroscopy

Abstract

The actions of pentachlorophenol (PCP) under various water salinities was investigated in live, intact red ( Haliotis rufescens) and black abalone ( H. cracherodii) by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy. Based on PCP toxicity in red abalone (6 h LC 50 1.6 mg l −1; 6 h NOEL=0.8 mg l −1), animals were exposed in flowing seawater (14°C) to a sublethal PCP concentration of 1.2 mg l −1 and a water salinity of either 25, 35 or 45 ‰. Phosphagen changes in foot muscle were monitored by surface-probe localized 31P NMR. Upon PCP exposure, phosphoarginine (PA) levels declined and inorganic phosphate (Pi) levels concurrently increased. Dosing was terminated at a standard metabolic endpoint (MEP), defined as the time for the spectral peak height for Pi to reach one-half that of PA. This was on average 3.3±0.2 and 6.8±0.7 h at ambient salinity; 5.3±0.7 and 7.1±0.7 h for high salinity; and 4.0±0.5 and 6.5±1.0 h at low salinity, for red and black abalone, respectively. During recovery, all biochemical endpoints returned to normal; however, both onset and intensity of effects were influenced by changes in seawater salinity. Disposition of [U- 14C]PCP in both species was also examined to determine if the effects observed with NMR had a kinetic basis. Three sets of abalone ( n=3) from each species were exposed to each salinity (25, 35 and 45 ‰), plus 1.2 mg l −1 of [U- 14C]PCP. Red abalone were exposed for 3.5 h and black abalone for both 3.5 and 6.5 h (they represent the lowest average MEP for both species). Residues were quantified via tissue digestion and liquid scintillation counting. The 3.5 h total concentration factors (TCFs) for red abalone were not significantly different among the three salinities ( P>0.05) and ranged from 104 to 133. However, low salinity seemed to deter the uptake of [U- 14C]PCP in black abalone, as the TCF was over three times lower for abalone exposed to 25 ‰ at both 3.5 h (TCF=19±11) and 6.5 h (TCF=38±8) than at 35 ‰ (3.5 h TCF=62±6; 6.5 h TCF=119±11) and 45 ‰ (3.5 h TCF=67±14, 6.5 h TCF=115±8). Furthermore, the 3.5 h TCF for red abalone exposed to PCP at all salinities was similar to the 6.5 h TCF for black abalone exposed at 35 and 45 ‰. Thus, black abalone appear to have greater resistance to the combined effects of PCP and salinity variations, which appears to be due to slower uptake of the biocide. While PCP is a potent uncoupler of mitochondrial oxidative phosphorylation, use of varying water salinities simulated an additional stress imposed on intertidal animals by transient or seasonal environmental changes.