Synthetics polymers derivatives of petroleum are
produced all over the world. Approximately 140 million ton per year are introduced
in the environment as industrial wastes products, which are accumulated because
their degradation is carried out slowly. This has a negative impact in the
ecosystems and organisms.
Considering the problematic of plastic wastes, in
this study was applied the biodegradation in two types of polymers: low density
polyethylene (LDPE) and polypropylene (PP). These polymers are extremely
recalcitrant, and the most persistent plastics dumped in the environment. To
carry out this biodegradation they used endophytic
fungal strains isolated from two endemic plants Psychotria flavida and Humboldtia
brunonis which produce laccase enzymes that have the capacity to degrade
these materials, the activity of enzyme was quantified in each species of fungi
viz. Cunnighamella echinulata,
Pestalotiopsis sp, Hypoxylon anthochroum, Paecilomyces lilacinus, Aspergillus sp,
Lasiodiplodia theobromae (Fig.1,2).
To be possible the biodegradation, the microorganism
has to join to the polymer forming biofilms and use it as a sole source carbon.
In this case were produced biofilms with different dose of irradiated gamma
which induce the photo-oxidation in two polymers, the dose was 0-1000 kGy for
LPDE and 0-100 kGy for PP (Fig.3,4). This generated a large surface area and
produced a great degree of hydrophobicity due to the introduction of carbonyl
groups that was used for endophytic fungi in their metabolisms enhancement the
biodegradation. The possible mechanisms is the transformation of carbonyl
groups to carboxyl groups in presence of oxygen (Fig.5) which undergo to B-
oxidation and subsequently undergo to cyclic acid citric, that results in the
production of CO2 and H2O (Fig.6). The efficiency for
degradation of the polymers was measured with the decrease in intrinsic
viscosity and average molecular weight of gamma irradiated.
Figure 1. Shows a) the formation for biofilm
fungi in the polymer and b) the presence of enzyme laccase.
Figure 2 Shows the activity of enzyme laccase
in each species of fungi where the production level of laccase in L. theobromae
was high (10.70 ± 1. U/ml) and in Hypoxylon anthochroum quite low (1.18 ± 0.10
U/ml).
Figura 3 shows percentage weight loss in gamma irradiated fungal inoculated LDPE films.
Figure 4 shows percentage weight loss in gamma irradiated fungal inoculated PP films.
Figure 5 shows (a) control film unirradiated (b) showed the peaks that correspond to addition of
oxygen and photoxidation compared with the control film. The gamma irradiated
LDPE (1000 kGy) rendered wavenumber 1712 cm-1 related to carbonyl group formation
which was absent in control. The area of peak at wavelength (3100-3500) cm-1 was broad and bended in irradiated (1000 kGy) fungal treated samples (c)
shows the presence of O-H stretching band of
hydroxyl groups and adsorbed water corresponding to decrease in
hydrophobicity and attributing to
degradation.
Figure 6 show the possible mechanisms for
biodegradation a) Gamma radiation and b) the efficiency for degradation by
fungi.
The biodegradation through irradiated gamma is
a biologic alternative for the problematic of plastic wastes. This study shows
that the radiation gamma can increase the capacity of microorganisms for use
the polymer as a sole carbon source in their metabolism producing enzymes that
degrade these materials.
If you have interested about the subject you can
search the next paper “Biodegradation of gamma irradiated low density
polyethylene and polypropylene by endophytic fungi”
-Reference
Sheik, S., Chandrashekar, K.R., Swaroop, K., & Somashekarappa,
H.M. (2015).Biodegradation of gamma irradiated low density polyethylene and polypropylene
by endophytic fungi.International Biodeterioration & Biodegradation.