hazardous是什么意思？

And, apparently, that day has come because seemingly routine operations such as knee replacements are now much more hazardous due to the looming threat of these infections.

Researchers studying teenagers in Israel concluded that, in that hazardous environment, mobile phones were regarded as "security objects" in parent-teen relationships―important because they provided the possibility ofcontact and communication at all times.

You know, forecasting's become a very hazardous business so I don't want to commit myself too much.