Special Issue Survey of Cetaceans in Captive Care

358 CouquiaudActivated Carbon—Activated carbon isamong the most effective materials for the physicalabsorption of organic carbon (Spotte, 1991).They are classified in the paragraph on mechanicalfiltration because they function on a physicalprinciple of absorption. These filters are made ofabsorbents manufactured from a number of carbonbasedmaterials. They typically have a 0.5 to 1 µmfiltration capability, making it helpful for particulatefiltration. Activated carbon commonly is usedfor dechlorination, for reducing soluble materialssuch as Dissolved Organic Carbon (DOC)—chloraminesissued from chlorination—and to preventthe accumulation of total organic carbon (TOC)precursors of trihalomethanes (THM; mutagenicand carcinogenic compounds present as traceconcentrations in chlorinated water and ozonatedseawater) in closed systems (Anonymous, 1999;Spotte, 1991). It can be installed on a side-streamafter mechanical filtration in combination withvarious oxidation systems. Activated carbon doesnot have a long life span and is quite expensive tochange. The disposed material has to be treated ashazardous waste (Spotte, 1991).Chemical PurificationRidgway (1972) calculated that a dolphin, weighing136 kg and eating 6.6 kg of fish, passes over4 l of urine and 1.4 kg of faeces per day. Themajority of this waste matter is soluble, and highlevels of organic nitrogen make a very good culturemedium for bacterial and fungal growth. Itis important to remove these matters by eliminatingthe water through an open circuit or throughthe use of oxidation in a closed system (Manton,1986). Chemical reactions also are related to temperature.The development of bacteria is acceleratedby high temperature.The objective of water sterilisation is to placethe agent in contact with microorganisms by themost efficient means. Two methods are used:(1) point-contact sterilisation (e.g., ozonation,UV irradiation) or (2) bulk-fluid (e.g., chlorination)(Spotte, 1991). Chemical purification alsoincludes catalysts such as copper and silver. Themost widely distributed systems used are chlorinationand ozonation. Chlorination still is used bya majority of facilities, but ozonation has becomequite popular. Chlorination as a single choice isin decline.Silver and Copper Catalysts—Metal ions, suchas silver and copper, used in conjunction withchlorination, are efficient for maintaining goodwater clarity, removing bacteria, and controlingalgae; however, copper toxicity has been reportedin marine mammals (Boness, 1996; McDevitt,1986) and copper might accumulate in the liver(Ford, 1997). Its use will therefore be avoided.Chlorination—Chlorine is one of the mostpopular chemical agents used for the eliminationof microorganisms and algae (Faulk, 1990); however,it is a difficult process and can give rise to anumber of problems (Boness, 1996; van der Toorn,1987). Injudicious use of such chemicals canbe more life-threatening than the organisms andexcreta they control (Geraci, 1986). As opposed toozone, chlorine generally is used as an oxidisingagent in the bulk-fluid and has a prolonged timeof action. Chlorine-based products are inexpensive,possess strong antimicrobial properties, andare easy to store and inject; however, they presentimportant disadvantages in that they form productswith lower oxidation potential—the chloramines—aswell as mutagenic and carcinogenicbyproducts (Spotte, 1991). Therefore, byproductsof the transformed chlorine are hazardous if notremoved by chemical processes or frequent waterrenewal.Chlorine is available as liquified gas (under pressureand referred to as liquid chlorine) and as solutionsof chlorine compounds such as sodium hypochlorite(Manton, 1986); however, as Geraci (1986)stated, chlorine as sodium hypochlorite is perhapsthe most commonly misused chemical treatment.When chlorine gas (Cl2) or sodium hypochloriteis mixed with water, it is transformed intohypochlorous acid (HOCl), which is an excellentoxidiser (Faulk, 1990; Manton, 1986; Spotte,1991). For optimal oxidation, pH has to be maintainedbetween 7.5 and 7.6. At higher pH levels,the concentration of hypochlorous acid, the activeagent, will drop, therefore reducing its sterilisationcapacities. Hypochlorous acid is highly unstable,however, as it breaks down with sunlight (Faulk1990). Free chlorine is the amount of hypochlorousacid and hypochlorite ions (OCl-) free andavailable to react. Hypochlorous acid reacts withammonia from urinary waste to form differentchloramines (monochloramine and subsequentlydichloramine and nitrogen trichloride). They persistlonger than free chlorine, but they possesslower oxidising potential (Spotte, 1991).Pool water is tested in dolphinaria for free andtotal chlorine. The survey showed that a safe rangeis below 0.2 ppm for free chlorine and 0.5 ppmfor total chlorine (combined residual chlorine).Saltwater test kits for chlorine and chloraminescan be used. Most of them give free and totalchlorine readings. Faulk (1990) recommends todelineate chloramines as well. Surveyed facilitiesperform these tests two to three times per day.Chlorine is a good bactericide; however, manyprotozoans, yeasts, cysts, and viruses are resistant(Boness, 1996). Skin infections are quite common inchlorinated water. It can be the result of the destructionof beneficial microflora and the inactivation of