title: The toxicity of metal mixtures to the estuarine mysid Neomysis integer (Crustacea: Mysidacea) under changing salinity.
abstract: Water quality criteria are mainly based on data obtained in toxicity tests with single toxicants. Several authors have demonstrated that this approach may be inadequate as the joint action of the chemicals is not taken into account. In this study, the combined effects of six metals on the European estuarine mysid Neomysis integer (Leach, 1814) were examined. Acute 96-h toxicity tests were performed with mercury, copper, cadmium, nickel, zinc and lead, and this as single compounds and as a mixture of all six. The concentrations of the individual metals of the equitoxic mixtures were calculated using the concentration-addition model. The 96-h LC50's for the single metals, at a salinity of 5 per thousand, ranged from 6.9 to 1140 microg/l, with the following toxicity ranking: Hg>Cd>Cu>Zn>Ni>Pb. Increasing the salinity from 5 to 25 per thousand resulted in lower toxicity and lower concentrations of the free ion (as derived from speciation calculations) for all metals. This salinity effect was strongest for cadmium and lead and could be attributed to complexation with chloride ions. The toxicity of nickel, copper and zinc was affected to a smaller extent by salinity. The 96-h LC50 for mercury was the same for both salinities. In order to evaluate the influence of changing salinity conditions on the acute toxicity of metal mixtures, tests were performed at different salinities (5, 10, 15 and 25 per thousand ). The 96-h LC50 value (1.49 T.U.) of the metal mixture, at a salinity of 5 per thousand, was clearly lower than the expected value (6 T.U.) based on the non-additive hypothesis, thus confirming the additive effect of these metals in the marine/estuarine environment. Changing salinity had a profound effect on the toxicity of the mixture. The toxicity clearly decreased with increasing salinity until 15 per thousand. Higher salinities (25 per thousand ) had no further influence on the 96-h LC50 of the mixture which is situated at a value between 4.4 and 4.6. Finally, the relative sensitivity to the selected metals was compared with the relative sensitivity of the commonly used mysid Americamysis (=Mysidopsis) bahia.
authors.affiliation: Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium. tim.verslycke@ugent.be
authors.forename: Tim
authors.initials: T
authors.lastname: Verslycke
authors.forename: Marnix
authors.initials: M
authors.lastname: Vangheluwe
authors.forename: Dagobert
authors.initials: D
authors.lastname: Heijerick
authors.forename: Karel
authors.initials: K
authors.lastname: De Schamphelaere
authors.forename: Patrick
authors.initials: P
authors.lastname: Van Sprang
authors.forename: Colin R
authors.initials: CR
authors.lastname: Janssen
mesh_terms: D000818:Animals; D002104:Cadmium / Q000737:chemistry / Q000633:toxicity; D003300:Copper / Q000737:chemistry / Q000633:toxicity; D003445:Crustacea / Q000187:drug effects*; D004347:Drug Interactions; D004781:Environmental Exposure; D007854:Lead / Q000737:chemistry / Q000633:toxicity; D007928:Lethal Dose 50; D008628:Mercury / Q000737:chemistry / Q000633:toxicity; D019216:Metals, Heavy / Q000737:chemistry / Q000633:toxicity*; D009532:Nickel / Q000737:chemistry / Q000633:toxicity; D012623:Seawater / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D013223:Statistics as Topic; D023382:Toxicity Tests, Acute; D014873:Water Pollutants / Q000032:analysis / Q000633:toxicity*; D015032:Zinc / Q000737:chemistry / Q000633:toxicity
chemical_list: D019216:Metals, Heavy; D014873:Water Pollutants; D002104:Cadmium; D007854:Lead; D012965:Sodium Chloride; D003300:Copper; D009532:Nickel; D008628:Mercury; D015032:Zinc