178 Environmental Biotechnology
The question of methane production, so central to the original thrust of the
legislation has been addressed by requiring sites to collect the landfill gas pro-
duced and use it for energy generation, conceding that it may be flared off where
for some reason this is not possible.
A second potential environmental problem typically associated with landfills is
the production of polluting leachates, which can be aggravated by the dumping of
biowaste. Water percolating through the site tends to leach out both organic and
inorganic substances which can lead to contamination of the groundwater. The
persistence of pathogens and the potential translocation of many biologically
active chemicals have recently become of increasing concern in the light of
growing (though largely circumstantial) evidence of health problems associated
with proximity to certain landfill sites. However, there is considerable variance
between many aspects of different facilities and, additionally, much uncertainty
as to the extent of any possible exposure to chemicals found therein (Vrijheid
2000). The UK government commissioned the world’s most extensive study to
date into the potential health risks of living within 2 kilometres of landfills,
to examine the incidence of low birth weight, congenital defects, stillbirths and
cancers in the vicinity of 9565 landfill sites, with a sample size in excess of some 8
million pregnancies. This revealed a 7% increase in the rate of both chromosomal
and nonchromosomal birth defects (Elliottet al. 2001) but the expert advisory
committee observed that this represented only a small excess risk and might well
be accounted for by factors other than those directly attributable to landfill itself.
While domestic landfill operations, then, may well be of little significant threat
to those around them, the situation for hazardous waste sites, though admittedly
less well investigated, appears somewhat different.
The findings of the recent, new investigation (Vrijheidet al. 2002) of data
originating from a smaller study of certain European landfills which accept haz-
ardous waste (Dolket al. 1998) suggests a 40% increase in chromosomal birth
defects and a 33% increase in the risk of nonchromosomal abnormalities, within a
3 kilometre radius. However, whether the observed increase in risk arises merely
from living near such a hazardous waste site, or as a result of other factors as
yet unknown, remains unclear. Greater understanding of the true scope of land-
fill releases, their potential toxicity and the possible exposure pathways will be
required to permit more meaningful interpretations of the epidemiological data
to be made.
Even where there is nothing to suggest an adverse effect on the local popula-
tion, high concentrations of biowaste-derived leachate remain undesirable. Such
rich liquors provide heterotrophic micro-organisms with a ready and abundant
source of food. In conditions of relatively low organic loading, a dynamic equi-
librium is reached between the bacteria breaking this material down and the
autotrophic organisms, typically algae, which subsequently make use of these
breakdown products. The oxygen balance works, since the requirements of the
aerobic decomposers is offset by the contribution of the photosynthetic algae