ABSTRACT
Aim: This study aimed to investigate the effects of nitrogen (NO3-N, NH3-N) and phosphorus (PO4-P) on the growth and microcystin production of two bloom-forming Microcystis species (toxic M. aeruginosa MAHC160824 and non-toxic M. viridis MVHC160824).Methodology: The two Microcystis species were isolated from the lower reaches of the Nakdong river, South Korea. In the culture experiments, the average nutrient concentrations (NH3-N, NO3-N and PO4-P) at which Microcystis appeared (> 15°C) was used as control medium. Different concentrations of NH3-N, NO3-N and PO4-P were then employed in nutrient testing (control, vs. 4 times and 16 times higher than the control). Microcystin levels were measured using a UPLC™ (LC MS/MS) system. Results: Both toxic and non-toxic Microcystis strains exhibited a maximum cell density at 30°C and a maximum growth rate at 25-30°C. In the nutrient addition assays, the maximum growth of two Microcystis species were found at nutrient concentrations 4 to 16 times higher than the control (NH3-N: 0.468 mg l-1, PO4-P: 0.100 mg l-1, NO3-N: 32.5 mg l-1). The highest microcystin production levels were found under optimal growth conditions. The microcystin levels of toxic M. aeruginosa MAHC160824 were below the detection limit despite a higher number of cells (> 300,000 cells ml-1) at the same nutrients concentrations as those found in raw water from the Nakdong river. Interpretation: Higher production of microcystin occurs when there is an increase in NH3-N and PO4-P within a restricted range in toxic species M. aeruginosa MAHC160824, else the production is low
ABSTRACT
In order to determine the contents of lead, cadmium and zinc, the tissues of the crussian carp, Carassius carassius, collected from the middle streams of the Nakdong river were examined. During the dry season from 8 to 15, March, 1987, six loci were selected to sample the fish and river water; five of them were the midstreams of the Nakdong river i.e., the vicinities of the Andong dam, the Nakdong bridge, the Waegwan bridge, Gangjung and Gaepori, the other one was the Kumho river around the Paldal bridge(see Fig.1). The microanalyses of lead and cadmium contents were undertaken by the atomic absorption spectrophotometer(Model IL-551) connected with CTF-IL 655, while that of zinc by the flame method with IL-551 only. The contents of lead and cadmium in water sampled from Gaepori distant from about 30km downward from the junction with the Kumho river were about 1.5 times higher than those from Gangjung distant about 0.5km upward from the junction, and the content of zinc from Gaepori was slightly higher than that from Gangjung. However, the contents of lead and cadmium in water sampled from Gaepori were three fifth of those from the vicinity of Paldal bridge far about 2km upperward from the junction. In the other words, the contents of lead and cadmium in the samples from the vicinity of the Paldal bridge were about 2.5 to 3 times higher than those from the Gangjung and 5 times higher than those from the Andong dam. The contents of the heavy metals in the tissues of Carassius carassius were relatively consistent to those of the aquatic environments were the fish were collected, with higher contents in the tissues of the crussian carp collected from the vicinity of Gaepori and the Paldal bridge which were so much polluted than in those from other loci in upper stream from the junction. And the contents of lead and cadmium in tissues were positively correlated with the age of the fish, however, that zinc was not. The contents of lead in bone of crussian carp from the vicinity of the Paldal bridge in the group of 0-1 year old fish were similar to those of 4-5 years old fish from Gaepori, and higher than those of 3-4 years old fish collected from the upper stream of the junction. It is likely that fishing from Gaepori and the paldal bridge is not recommended, and all the industrial producers have to pay intensive attention to the water pollution due to the sewage disposal.