Toxicity Of Some Environmental Pollutants To Marine Crustaceans Artemia Sinica,(Anostraca: Artemiidae) And Exopalaemon Carinicauda,(Decapoda: Palaemonidae)

BackgroundTo safeguard the marine environment, there is an urgent need to establish standardizedmethods to analyze the acute toxicity of pollutants to aquatic organisms. As a first step toestablish a simple, inexpensive and reliable short-term routine bioassay to test the toxicityof some environmental pollutants, in this dissertation, I investigated the usefulness of thebrine shrimp Artemia sinica as a test species to study the acute toxicity of severalphenolic compounds and heavy metals. A. sinica was chosen as the test species due to itsincessant availability in the form of dry cysts which can be hatched with little effort, andits flexibility to varied nutrient resources as it is a non-selective filter feeder. I also testedthe antioxidant enzyme activities of ridgetail white prawn Exopalaemon carinicauda inresponse to naphthalene. This species has strong tolerance to the change of environmentalfactors, hence it is easy to culture them in laboratory; it has a high reproduction capacity with a short reproduction cycle (only two months) and maintains reproductive capacityall year round. Thus, it is available for experiments at any time. The evaluation of theacute toxicity of the pollutants was based on the median lethal concentration (LC50s).Results and ConclusionSection1. Bioassays using A. sinica. I examined the acute toxicity of several phenoliccompounds and heavy metals to the laboratory cultured nauplii and adults of A. sinica.The results indicated that A. sinica nauplii could resist a significantly higherconcentration of heavy metals compared to phenolic compounds. The toxicity order wasn-Nonylphenol (n-NP)4-t-Octylphenol (4-t-OP)2-4-dichlorophenol (2-4-DCP)bisphenol-A (BPA) for phenolic compounds, and Cu (CuSO4·5H2O) Cr (Na2CrO4)>Cd (CdCl2·2.5H2O)> Pb [Pb(CHCOO)2·3H2O] for heavy metals.Another bioassay was also conducted on the acute toxicity of five phenoliccompounds to the15day-cultured A. sinica. The toxicity order of the phenoliccompounds was n-hexylphenol (n-HP)> n-NP> t-butyl phenol (t-BP)>2,-4-DCP>BPA. The LC50sof the tested chemicals obtained by regression analysis demonstrates thedependency of the responses (dose response relationship) to phenolic exposure. Asignificant difference of toxicity (LC50) values was recorded between and within thegroups of five tested compounds. The24-hr LC50value revealed that the toxicity of n-HPis62.4times to that of BPA,5.5time to t-BP,4.1and2.7times to2,-4-DCP and NP,respectively.I also evaluated the effectiveness of the chorion of A. sinica cysts (shell) as abarrier against nonylphenol exposure. Both whole and decapsulated cysts were exposed to seawater containing5μgL1nonylphenol during their hydration and hatching phase.The concentration of nonylphenol was found highest in the exposed decapsulated cysts,then in the whole cysts, and lowest in the embryos with the chorions removed. Theseresults indicated that nonylphenol was blocked by the shell.Section2. Bioassay using Exopalaemon carinicauda. I examined the antioxidantenzyme activities in Exopalaemon carinicauda in response to naphthalene. The aim ofthis experiment was to evaluate the efect of different concentrations of naphthalene onthe antioxidant defenses in cephalothorax of juvenile shrimp E. carinicauda. This is thefirst report of the cephalothoraxic antioxidant response of shrimps to naphthaleneexposure. The shrimps were exposed to six diferent concentrations. Groups ofnaphthalene (160–318μg/l) for4days and then cephalothoraxic tissues were dissectedfor measurement of the activities of antioxidant enzymes including Catalase (CAT),Superoxide Dismutase (SOD), Glutathione S-transferase (GST) and GlutathionePeroxidase (GPx); CAT responded to naphthalene exposure significantly in Group3 (p<0.05) and4(p<0.01) and reached the maximum in Group4with an activation rate upto38.4%. SOD was also induced significantly by naphthalene in Groups2,3and4(p<0.05) and highly significantly in Group5(p<0.01) with an induction rate of23.5%.The activity of GPx was not greater in the exposed shrimp and the response was similarbetween Groups3,46, and7, but the activity was significantly affected only in Group5(p<0.05), with an activation rate of35.6%. Similarly, GST activity was induced highlysignificantly (p<0.01) only in Group4with an activation rate up to42.2%. Thus, all ofthe above antioxidant defense enzymes are inducible enzymes; however, when theanimals were exposed to a higher exposure concentration of naphthalene, all enzymeactivities decreased, indicating that a severe oxidative stress was restraining the activitiesof these enzymes.