2. Health risk assessment for
farmers
Health risk can be localized in the different activities in
the field when, the farm workers use compost, urine and greywater to amend the
soil and the crops.
2.1. Spreading compost
When using fertilizer products containing human or animal
excreta, the reduction of excreted pathogens is a critical step in minimizing
the risk of further spreading of pathogens.Transmission of disease may occur if
humans or animals come in contact with the excreta and accidentally ingest the
pathogen-containing material before the pathogens have been inactivated
(Schönning et al., 2007).According to WHO, (2006a) the variations in the
risk for infection depend on the organism in question. Some Salmonella are able
to regrow in stored but unstabilized materials, especially if the materials are
partly moist. Viruses and parasites generally have longer survival in the
environment as well as lower infectious doses, which resulted in high risks for
rotavirus, the protozoa and Ascaris.For WHO, (2006a), in considering
two mean scenarios which are unconditional (applying the incidence in the
population) and conditional (assuming that one member of the family actually
had an infection during period of collection). Thus in this situation, the
difference in risk between the conditional and unconditional scenario was 1-4
orders of magnitude, and the difference between typical (50%) and worst case
(95%) varied from none to five orders of magnitude, depending on the organism.
For the unconditional scenario, the risk was never higher than
4x10-2 (rotavirus). Only after 12 months of storage and taking
incidence into consideration were the risks <10-4 for all
organisms, excluding Ascaris (Pinf = 8 x 10-4),
when emptying the container and applying the material(WHO, 2006a);
(Schönning et al., 2007).For -Carr, (2005), agricultural field workers are
at high risk of parasitic infections because of the long survival of the
protozoa and Ascaris in the compost because WHO guidelines recommend
to reduce the helminth eggs in compost to = 1 egg/L (WHO, 2006a). But
exposure to hookworm infection can be reduced, even eliminated, by the use of
less contaminating irrigation methods and by the use of appropriate protective
clothing (i.e. shoes for field workers and gloves for crop handlers).
2.2. Spreading urine
For the hygienic risks related to the handling and reuse of
urine, temperature, dilution, pH ammonia and time are the mean determinants
affecting the persistence of organisms in collected urine (WHO, 2006a). Urine
contains the majority of plant macronutrients that originate from household
wastewater (Swedish EPA, 2007). Furthermore, the potential pathogen content is
low, especially compared to faeces. Therefore, separate collection of urine for
later use as a fertilizer in agriculture has been promoted through the use of
urine separating toilets and latrines (Höglund et al., 2002).The short
survival of E. coli in urine makes it unsuitable as a general
indicator for faecal contamination by, for example, viruses and protozoa(WHO,
2006a).According to WHO(2006a), the Gram-positive faecal streptococci has a
longer survival process (normally a T90 value of 4-7 days at
20°C, but up to 30 days at 4°C), and spore-forming clostridia are
not reduced at all during a period of 80 days. In general, lower temperature
and higher dilution result in longer survival of most bacteria (Höglund et
al., 1998; WHO, 2006). However, the urine is generally contaminated at the time
of the micturition by germs coming from faeces, which increases the load of
pathogenic and constitutes a health risk (Tagro, 2012). According to WHO
(2006a), the pathogenic germs of bacterial, viral or parasitic origin are
responsible for several diseases such as diarrhea, cholera, typhoid fever,
salmonellosis, shigelloses, amoebiasis, bacterial dysentery, amoebic
dysentery, and parasitism. But, urinary excretion of pathogens that can be
transmitted through the environment are uncommon (Höglund et al., 2002).
The use of non-treated urines as fertilizer in agriculture can contribute to
the transmission of these diseases to the directly exposed field workers
(Tagro, 2012). However if the farm workers are used the protective equipment
before spreading of urine in the field, the risk of infection can be
reduced(WHO, 2006a). Furthermore, Höglund et al., 1998 suggest that
estimate the risk of pathogen transmission for handling, transportation and
reuse of source separated urine that follow it is necessary to determine the
exact amount of faecal material introduced in the urine fraction.
Therefore, the estimated risks of pathogens for different
pathways were calculated by Höglund et al., 2002 for three indicator
pathogens (C. jejuni, C. parvum and rotavirus). It arises that in the
case of an epidemic, where no inactivation and accidental ingestion of 1 mL of
unstored urine was assumed to occur in the collection tank and spreading in the
field, viruses may pose an unacceptably high risk, and bacteria pose a greater
risk than protozoa. The annual risk of viral infection at 4°C is 0.81,
since very low inactivation of rotavirus occurs at this temperature and
slightly lower at 20°C (Pinf = 0.55) (WHO, 2006a). The risk
from exposure to aerosols when farm workers spread urine in the field depend,
according to Höglund et al., 2002 and WHO, 2006 of the technique of
spreading of the urine.
|
|
