Are people living near graveyards at increased risk of exposure to biohazards?
Do you ever wonder: in those houses built strategically next to graveyards, are the occupants drinking residual waste products (or atoms that the body is composed of) of those buried next to them? Think about it--if they're drinking well water, coffins begin to break down over time, right? Is it plausible to assume they are consuming their beloved deceased? Just something I have always thought about.
Get a grip, champ. You bring up a subject that most people most of the time are happy not to think about. Every so often, however, some innocent realizes: Wait--cemeteries are full of dead bodies! GROSS! Although I have to say your liquid cannibalism angle is an innovative twist.
Years ago people seemingly had greater cause for concern. In 1839 a British surgeon named George Alfred Walker published a book entitled Gatherings from Grave Yards, Particularly Those of London, With a Concise History of the Modes of Interment Among Different Nations From the Earliest Periods, and a Detail of Dangerous and Fatal Results Produced by the Unwise and Revolting Custom of Inhuming the Dead in the Midst of the Living. Walker wasn't troubled so much by the stray atoms that might work loose from a cadaver as by the good-size chunks--London graveyards were so crammed with corpses that grave diggers were frequently obliged to hack through old and not-so-old coffins in order to make space for new ones. Not only was the pileup of putrefying bodies disgusting and disrespectful of the departed, Walker felt, it led to debility and disease among those still present. He mentioned contaminated well water in his writings, but his real concern was "the deadly emanations of human putrescence" or "malaria" (literally, bad air), which he suggested might be a cause of "typhus fever" among other things. It wasn't--the different forms of typhus are transmitted by insects, while typhoid fever is caused by waterborne bacteria. Nonetheless, during the 19th century municipal officials throughout Europe and North America were sufficiently alarmed by such warnings that they outlawed the opening of new cemeteries within city limits and sought to relocate old ones to the hinterlands.
Today we know that methane and other gases released by decomposition, while not entirely benign, don't cause disease. As you rightly suspect, the real danger, if there is one, is groundwater contamination. Local regulations typically forbid burials below the water table, specify minimum distances between wells and burial grounds, and so on. For a long time most people were content to leave it at that, but over the past decade or so a few scientists and environmental officials in various parts of the world have felt moved to investigate just how serious a public-health threat cemeteries actually were. In general they found that (a) remarkably little research has been done on the subject, (b) elevated levels of contaminants can be detected at some grave sites, (c) contamination generally decreases significantly the farther you get from the sites, and (d) overall there's little evidence that cemeteries have much impact on groundwater. Australian hydrogeologist Boyd Dent, an expert on cemetery-related environmental issues, put the matter bluntly in the title of a 1998 paper: "Cemeteries: A Special Kind of Landfill." In other words, cemeteries represent a manageable risk.
All that having been said, the last word on the subject is a long way from written. Some researchers wonder whether embalming fluid is dangerous, the older stuff in particular--in the late 1800s morticians commonly pumped cadavers full of solutions containing arsenic, sometimes as much as two pounds of it per body. The "green burial" movement, a dust-to-dust approach in which the dead are interred without embalming fluid and sometimes without coffins, is likewise apt to drive more study, as advocates attempt to placate the squeamish public. On a related matter, some public-health types are trying to make the media and the public understand that dead bodies aren't inherently dangerous and thus there's no need for mass burials following natural disasters, which make it impossible to identify the dead.
Finally, let's face it, there's a lot about what happens after they lay you in the cold, cold ground that we just don't know. Boyd Dent, I notice, has been publishing quite a few papers lately about adipocere, also known as grave wax. For reasons still poorly understood, corpses don't invariably decompose into potting soil as many assume. Instead, the fat tissue, usually in the presence of moisture, sometimes turns into a solid, soaplike substance that makes the cadaver look like something you'd find in a wax museum, albeit the George Romero wing. The Internet being the boon to humanity that it is, you can find numerous full-color examples in milliseconds by googling adipocere, lest you lack visuals as you contemplate our icky common fate.