Abstract
Pollutants and other external factors effect the strength and service life of fishing nets. The effects of some pollutants such as heavy metals and temperature on the mesh breaking strength of knotless polyamide (PA) fishing nets were determined in this study. The PA net samples were subjected to heavy metal solutions containing Cd (Cadmium), Cu (Copper), Ni (Nickel), Hg (Mercury), Zn (Zinc), Cr (Chromium) and Pb (Lead) for 14 days at 99°C in metal and glass containers. Also, the samples were hold on metal and glass surfaces and suspended in the air at 130 and 175°C for the periods of 30 min., 1 and 2 hours. The order of breaking strenght values of heavy metal treated samples in metal containers was found Ni> Cd >Pb > Zn> Hg> Cu> Cr, respectively, whereas the order of samples was Cr> Hg> Cu> Pb> Zn> Cd> Ni for glass containers. Regarding to the test conditions and the temperature, the breaking strenght values of samples treated with 130°C were found significantly high (p˂0.05) compared with those hold at 175°C for both metal and glass surfaces and air suspended groups in all durations.
Highlights
Fisheries have developed continuously over the centuries, utilising improved and larger ships, more sophisticated fishing equipment and catch preservation techniques
The mesh breaking strength of 36/18 fishing net samples in metal and glass containers after exposure to heavy metal solutions at 99 °C for 14 days, show that the samples treated in metal containers lost their strength much more than those of samples treated in glass containers
For the samples treated with metal solutions in metal containers, the order of breaking strength values is Ni>Cd>Pb>Zn>Hg>Cu>Cr whereas the order was Cr>Hg>Cu>Pb>Zn>Cd>Ni in glass containers
Summary
Fisheries have developed continuously over the centuries, utilising improved and larger ships, more sophisticated fishing equipment and catch preservation techniques. Most net cages are made of square mesh knotless Polyamide (PA) netting and Polyester (PES), Polyethylene (PE), Polypropylene (PP) and Polyvinyl alcohol (PVAA) ropes (Ramos 1999; Klust 1982; Moe et al 2007). Materials are degraded most often by sunlight, thermal effects and moisture Other factors such as air contaminants, oxygen and salt can contribute to degradation. High humidity is known to accelerate the rates of degradation of several classes of plastics. This may be brought about by the plasticizing action of small quantities of sorbed water leading to increased accessibility of the matrix to atmospheric oxygen or by the leaching out of stabilizing additives from the formulation (Andrady 1990). Plastics at sea will not suffer from such temperature build up and may undergo slower oxidative degradation and photodegradation (Boxhammer 1999; Boxhammer & Scott 1999; Summers & Rabinovitch 1999; Masters & Bond 1999; Wypych & Faulkner 1999)
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