Effects of high ammonia concentrations on three cyprinid fish: Acute and whole-ecosystem chronic tests.

A number of studies have revealed ammonia to be toxic to aquatic organisms; however, little is known about its effects under natural conditions. To elucidate the role of ammonia, we conducted 96-h acute toxicity tests as well as a whole-ecosystem chronic toxicity test for one year in ten 600-m2 ponds. Three common cyprinids, silver carp Hypophthalmichthys molitrix Val. (H.m.), bighead carp Aristichthys nobilis Richardson (A.n.), and gibel carp Carassius auratus gibelio Bloch (C.g.), were used as test organisms. The 96-h LC50 values of un-ionized ammonia (NH3) for H.m., A.n., and C.g. were 0.35, 0.33, and 0.73mgL-1, respectively. In the ponds, annual mean NH3 ranged between 0.01 and 0.54mgL-1, with 4 ponds having a NH3 higher than the LC50 of A.n. (lowest LC50 in this study). No fish were found dead in the high-nitrogen ponds, but marked histological changes were found in livers and gills. Despite these changes, the specific growth rate of H.m. and A.n. increased significantly with NH3. Our pond results suggest that fish might be more tolerant to high ammonia concentrations in natural aquatic ecosystems than under laboratory conditions. Our finding from field experiments thus suggests that the existing regulatory limits for reactive nitrogen (NH3) established from lab toxicity tests might be somewhat too high at the ecosystem conditions. Field-scale chronic toxicity tests covering full life histories of fish and other aquatic organisms are therefore encouraged in order to optimize determination of the effects of ammonia in natural environments.

Effects of high nitrogen concentrations on the growth of submersed macrophytes at moderate phosphorus concentrations.

Eutrophication of lakes leading to loss of submersed macrophytes and higher turbidity is a worldwide phenomenon, attributed to excessive loading of phosphorus (P). However, recently, the role of nitrogen (N) for macrophyte recession has received increasing attention. Due to the close relationship between N and P loading, disentanglement of the specific effects of these two nutrients is often difficult, and some controversy still exists as to the effects of N. We studied the effects of N on submersed macrophytes represented by Vallisneria natans (Lour.) Hara in pots positioned at three depths (0.4 m, 0.8 m, and 1.2 m to form a gradient of underwater light conditions) in 10 large ponds having moderate concentrations of P (TP 0.03 ± 0.04 mg L(-1)) and five targeted concentrations of total nitrogen (TN) (0.5, 2, 10, 20, and 100 mg L(-1)), there were two ponds for each treatment. To study the potential shading effects of other primary producers, we also measured the biomass of phytoplankton (ChlaPhyt) and periphyton (ChlaPeri) expressed as chlorophyll a. We found that leaf length, leaf mass, and root length of macrophytes declined with increasing concentrations of TN and ammonium, while shoot number and root mass did not. All the measured growth indices of macrophytes declined significantly with ChlaPhyt, while none were significantly related to ChlaPeri. Neither ChlaPhyt nor ChlaPeri were, however, significantly negatively related to the various N concentrations. Our results indicate that shading by phytoplankton unrelated to the variation in N loading and perhaps toxic stress exerted by high nitrogen were responsible for the decline in macrophyte growth.

[Alleles of HLA class II DRB1 of patients with essential hypertension in Yunnan Hans].

OBJECTIVE: To investigate the association between the alleles of human leukocyte antigens (HLA)-DRB1 and essential hypertension (EH) in the Hans living in Yunnan of China. METHODS: The alleles of HLA-DRB1 were typed by polymerase chain reaction-sequence specific primers (PCR-SSP) technique in samples from 83 patients with essential hypertension and 91 healthy controls. All of the subjects, their grandparents and grand-grandparents are Hans living in Yunnan of China. RESULTS: The frequency of DRB1*1501/2 in the EH patients (0.219) was significantly higher than that in the controls(0.060), chi quare=18.331, P<0.01. Relative risk (RR) was 4.46, and etiologic factor (EF) was 0.34. The frequency of DRB1*0901 significantly decreased in the group of patients with EH in comparison to the controls (0.081 versus 0.192) chi-square=8.704 P<0.05. RR was 0.41 and prevention factor(PF) was 0.19. CONCLUSION: HLA-DRB1*1501/2 is associated with the susceptibility to essential hypertension in the Yunnan Hans of China. DRB1*0901 may protect one from the disease.