Quantification of Phosphorus species, total phosphorus and phosphates in marine and freshwater samples and in fish feed from fish farms using spectrophotometry.

Abstract

Phosphorus (P) is very important for plant growth and is a key element in animal‘s many physiological and biochemical processes. However, the excess of phosphorus in waters causes eutrophication which in turn causes the death of aquatic life due to the decrease of dissolved oxygen levels. To control eutrophication, total phosphorus is recommended to be no more than 0.05 mg/L in streams that enter lakes and 0.1 mg/L in flowing waters. This work aims to determine total phosphorus and PO4-3 in marine water, freshwater from fish farms and fish feed using the ascorbic acid method followed by spectrophotometric quantification. The calibration curves of both total P and PO4-3 were performed and the R2 values were 0.999 for both. The analysis of water from different fish farms was carried out. The results show that the marine waters have a higher concentration of P and PO4-3 than freshwaters. The total P and PO4-3 in the fish farm‘s outflow water is higher compared to the inflow water specially in the case of marine water. However, all the concentrations found were below the Portuguese legal limits for the kind of water analyzed. On the other hand, the analysis of the fish feed water suspension simulating feed waste, showed that dissolution of both P and PO4-3 increased with time and the contribution of particulate P was high. Finally, the results of this work show the high efficiency of ascorbic acid method to quantify the total P and PO4-3 in water samples. This method could be used to control the P content as well as the eutrophication of waters.