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This study investigated the effect of nitrogen (N) and phosphorous (P) stress on the production of DHA or EPA and total fatty acids (TFAs) in the marine microalga Tisochrysis lutea and the freshwater microalga Monodus subterraneus. Five N or P starvation/limitation conditions (N sufficient and P limited, N sufficient and P starved, N starved and P sufficient, N starved and P limited, and N and P starved) and one N and P sufficient condition (control) were studied. The results demonstrated that the proportion of DHA or EPA among TFAs and production in the microalgae suspensions decreased (57%, 73% for N stress and 18%, 51% for P stress, respectively) under N or P stress in both microalgae compared with the N and P sufficient group. Differently, DHA dry weight content of T. lutea decreased significantly, and EPA dry weight content of M. subterraneus decreased slightly under N starved conditions. Clear differences in TFA content/production and the relationship between TFA and DHA or EPA production/content and CO2 fixation were observed between the two microalgae. These results give a new sight on the difference between marine microalgae and freshwater microalgae. Meanwhile, it gave a potential application to produce DHA or EPA and TFA combining with CO2 fixation by these microalgae.

This paper evaluated the excretion masses and environmental occurrence of 11 classes of 50 antibiotics in six typical swine and dairy cattle farms in southern China. Animal feeds, wastewater and solid manure samples as well as environmental samples (soil, stream and well water) were collected in December 2010 from these farms. Twenty eight antibiotics, including tetracyclines, bacitracin, lincomycin, sulfonamides, fluoroquinolones, ceftiofur, trimethoprim, macrolides, and florfenicol, were detected in the feeds, animal wastes and receiving environments. The normalized daily excretion masses per swine and cattle were estimated to be 18.2mg/day/swine and 4.24 mg/day/cattle. Chlortetracycline (11.6 mg/day/swine), bacitracin (3.81 mg/day/swine), lincomycin (1.19 mg/day/swine) and tetracycline (1.04 mg/day/swine) were the main contributors to the normalized daily excretion masses of antibiotics per swine, while chlortetracycline (3.66 mg/day/cattle) contributed 86% of the normalized daily excretion masses of antibiotics per cattle. Based on the survey of feeds and animal wastes from the swine farms and interview with the farmers, antibiotics excreted by swine were mainly originated from the feeds, while antibiotics excreted by dairy cattle were mainly from the injection route. If we assume that the swine and cattle in China excrete the same masses of antibiotics as the selected livestock farms, the total excretion mass by swine and cattle per annum in China could reach 3,080,000 kg/year and 164,000 kg/year. Various antibiotics such as sulfonamides, tetracyclines, fluroquinolones, macrolides, trimethoprim, lincomycin and florfenicol were detected in well water, stream and field soil, suggesting that livestock farms could be an important pollution source of various antibiotics to the receiving environments.