Male reproductive organs are at risk from environmental hazards

Male reproductive disorders that are of interest from an environmental point of view include sexual dysfunction,infertility,cryptorchidism,hypospadias and testicular cancer. Several reports suggest declining sperm counts and increase of these reproductive disorders in some areas during some time periods past 50 years. Except for testicular cancer this evidence is circumstantial and needs cautious interpretation. However,the male germ line is one of the most sensitive tissues to the damaging effects of ionizing radiation,radiant heat and a number of known toxicants. So far occupational hazards are the best documented risk factors for impaired male reproductive function and include physical exposures （radiant heat,ionizing radiation,high frequency electromagnetic radiation）,chemical exposures （some solvents as carbon disulfide and ethylene glycol ethers,some pesticides as dibromochloropropane,ethylendibromide and DDT/DDE,some heavy metals as inorganic lead and mercury） and work processes such as metal welding. Improved working conditions in affluent countries have dramatically decreased known hazardous workplace exposures,but millions of workers in less affluent countries are at risk from reproductive toxicants.New data show that environmental low-level exposure to biopersistent pollutants in the diet may pose a risk to people in all parts of the world. For other toxicants the evidence is only suggestive and further evaluation is needed before conclusions can be drawn. Whether compounds as phthalates,bisphenol A and boron that are present in a large number of industrial and consumer products entails a risk remains to be established. The same applies to psychosocial stressors and use of mobile phones. Finally,there are data indicating a particular vulnerability of the fetal testis to toxicants-for instance maternal tobacco smoking. Time has come where male reproductive toxicity should be addressed form entirely new angles including exposures very early in life.

The effects of nitrogen fertilizer application on methane and nitrous oxide emission/uptake in Chinese croplands

The application of nitrogen（N） fertilizer to increase crop yields has a significant influence on soil methane（CH_4） and nitrous oxide（N_2O） emission/uptake.A meta-analysis was carried out on the effect of N application on（i） CH_4 emissions in rice paddies,（ii） CH_4 uptake in upland fields and（iii） N_2O emissions.The responses of CH_4 emissions to N application in rice paddies were highly variable and overall no effects were found.CH_4 emissions were stimulated at low N application rates（〈100 kg N ha^（-1）） but inhibited at high N rates（〉200 kg N ha^（-1）） as compared to no N fertilizer（control）.The response of CH_4 uptake to N application in upland fields was 15%lower than control,with a mean CH_4 uptake factor of-0.001 kg CH_4-C kg^（-1） N.The mean N_2O emission factors were 1.00 and 0.94%for maize（Zea mays） and wheat（Triticum aestivum）,respectively,but significantly lower for the rice（Oryza sativa）（0.51%）.Compared with controls,N addition overall increased global warming potential of CH_4 and N_2O emissions by 78%.Our result revealed that response of CH_4 emission to N input might depend on the CH_4concentration in rice paddy.The critical factors that affected CH_4 uptake and N_2O emission were N fertilizer application rate and the controls of CH_4 uptake and N_2O emission.The influences of application times,cropping systems and measurement frequency should all be considered when assessing CH_4 and N_2O emissions/uptake induced by N fertilizer.