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Page 1: Investigatory Project

Julian Paolo BiyoJason Andrei TemeloI-RubyPhilippine Science High School Western Visayas Campus

Investigatory Project

TITLE: Effect of the Different Types of Substrates on the Biodegradability of SM Plastic Bags

I. Background of the Study

Official figures show that plastics make up around 25% of the garbage that metro manila churns out, while an independent survey conducted by Ecowaste Coalition and Greenpeace on the composition of discards on manila bay in 2006 found that 51% were plastic bags, 19% sachets and junk food wrappers, 5% Styrofoam, 1% hard plastics, 10% rubber, 13% biodegradable wastes (Cayetano, 2008; www.senatorpiacayetano.com/psc/pressreleasedetails.php?recordID=175)

Biodegradable plastics are degradable plastics on which the degradation results from the action of naturally occurring micro-organisms such as bacteria, fungi , and algae ([email protected]). These plastics are broken down into water, carbon dioxide, methane and biomass primarily through enzymatic action on microorganisms(Azios, 2007 www.csmonitor.com/2007/1219/p16s01 -sten.html ). Biodegradable will fully disintegrate in six months or less. It turns into powder and blends with the soil after a few months (Demetillo, 2008 www.smprime.com/News.php?BlurbID=1113).

Many biodegradable plastics will decompose in industrial plants, backyard compost piles, or open environments. The inherent biodegradability of plastics depend on several environmental factors such as moisture, temperature, surface area, and the manufacturing method of the finished product. (Nolan-ITU Pty Ltd, 2002 www.environment.gov.au/settlement/publications/waste/deg )

Although some brands claim to be biodegradable in open air and saltwater, virtually no decomposition occurs within a closed landfill that has been capped, preventing air circulation. (Azios, 2007 www.csmonitor.com/2007/1219/p16s01 -sten.html )

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The SM mall chain has started shifting biodegradable plastic bags for its supermarkets and department stores (Cayetano, 2008). The use of biodegradable plastics help lessen the burden of the ever-growing garbage problem in the Philippines and in the whole world

II. Problem of the Study

This study was conducted to answer the following problem:

Will exposing the SM plastic bags to different substrates such as compost soil, loam soil, tap water, and seawater over a period of time affect its biodegradability?

III. Hypothesis of the Study

If SM plastic bags will be placed in different substrates over a period of time, then its biodegradability will be affected.

IV. Objectives of the Study

A. General Objective:

To determine the effect of different substrates on the biodegradability of SM plastic bags.

B. Specific Objectives:

1. To expose SM plastic bags to different substrates such as compost soil, loam soil, seawater and tap water for a duration of several months.

2. To measure the weight of the plastic bags (grams) before and after different exposure periods to the substrates.

3. To compare the percent weight loss of the SM plastic bags exposed to different substrates after a period of time.

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V. Design of the Study

A. Variables

A1. Independent variables/ manipulated variable: substrate1. Compost soil2. Loam soil3. Seawater4. Tap water

A2. Dependent variable/ responding variable: biodegradability (percent weight loss)

B. Materials

6, 1-litre glass jars 6, 7”x9” aluminium trays 12 pcs. 3”x4” SM plastic bags 500g loam soil 500g compost soil 500mL seawater 500mL tap water Analytical balance Graduated cylinder Weighing scale

C. Procedures

We cut the SM plastic bags into 3”x4”sizes strips. We labelled the plastic strips into C1, C2, C3 for compost soil, L1, L2, L3 for loam soil, S1, S2, S3 for seawater, and T1, T2, T3 for tap water treatments. We then determined the initial weights of the plastic strips in grams using the analytical balance. The initial weights (W1) of the plastic strips were then recorded in our log book.

Three aluminium trays (7”x9”) were labelled C1, C2 and C3. Five hundred grams of compost soil were measured using a weighing scale and placed in each tray. Another three aluminium trays (7”x9”) were labelled L1, L2, and L3. Five hundred grams of loam soil were placed in 3 each tray.

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One hundred mL of tap water were mixed with the soils. Plastic strips labelled C1, C2 and C3 were placed in trays labelled C1,C2 and C3 containing compost soils. Plastic strips L1, L2 and L3 were placed in trays L1, L2 and L3 containing loam soil.

Five hundred mL of seawater were placed each in three glass jars. The jars were labelled S1, S2 and S3. In another three jars, 500mL of tap water were placed. The jars were labelled T1, T2 and T3. Plastic strips labelled S1, S2 and S3 were placed in jars containing seawater while plastic strips T1, T2 and T3 were placed in jars containing tap water. The plastic were immersed in the different substrates last September 9, 2008.

The set-ups were placed in the Biology laboratory room and were observed from time to time. Physical observations of the plastic strips were made on the following dates: September 24, 2008, October 6, 2008, and November 15, 2008.

Last November 15, 2008, the plastic strips were harvested from the different substrates. They were washed with tap water and air dried for 48 hours. Physical changes in each strip were noted and recorded. Pictures of the plastic strips were also taken to observe changes before they were immersed in the different substrates and after immersion for about two months. The dry weights in grams of each plastic strip were measured using an analytical balance. Results were recorded in the log book.

The plastic strips were again were submerged to the different substrates for further observations.

Percent weight loss in each plastic strip was determined using the formula:

Percent weight loss= Initial weight (W1) – Final weight (W2) / Initial weight x 100

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Plate 1. SM plastic strips (3”x4”) used in the experiment.

Plate 2. Measuring the initial weight of the SM plastic strips.

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Plate 3. Preparing the soil substrates.

Plate 4. Recording the initial weights of the plastic strips.

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Plate 5. Plastic strip immersed in loam soil.

Plate 6. Plastic strips immersed in seawater and tap water.

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VI. Results of the Study

On September 24, 2008, 22 days after the plastics were submerged to the different substrates, the plastic strips were harvested to observe any physical change. No physical change was observed in any of the strips. On October 6, 2008, a month after the immersion, the plastic strips were again observed. No physical change was seen in any of the plastic strips.

On November 8, 2008, 66 days after the plastic strips were immersed, they were harvested, washed with tap water and air dried for 48 hours. This time, almost all the strips showed physical changes such as the appearance of small holes, thinning in some portion, and discoloration.

Plate 7. Thinning and discoloration observed in plastic strip immersed in loam soil for 68 days.

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Plate 8. Thinning and tearing in some portions of the plastic strip submerged in seawater for 68 days.

Plate 9. Discoloration observed in plastic strip submerged in compost soil for 68 days

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Table 1. Percent weight loss in SM plastic strips exposed to different substrates after 68 days exposure period.

Treatment

Replicate

Initial weight(g)(Sept. 9, 2008)

Final weight(g)(Nov. 15, 2008)

% weight loss

Compost C1 0.3474 0.2422 30.28

C2 0.4230 0.4226 0.09

C3 0.3524 0.2556 24.47

Mean= 18.28

Loam L1 0.3902 0.3490 10.56

L2 0.4013 0.3440 14.27

L3 0.3945 0.3895 1.26

Mean= 8.70

Tap water T1 0.4114 0.4099 0.37

T2 0.3618 0.3248 10.22

T3 0.4275 0.4240 0.82

Mean= 3.80

Seawater S1 0.3643 0.2788 23.47

S2 0.3593 0.2630 26.8

S3 0.3487 0.3175 8.95

Mean= 19.74

Overall mean=

12.63

Table 2: Qualitative observations on SM plastic strips exposed to different substrates after several days duration of exposure.

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Substrate Sept. 24, 2008 (16 days exposure)

Oct. 6, 2008(28 days exposure)

November 15, 2008(68 days exposure)

Compost Soil No physical change observed

No physical change observed

Thinning in some portions of the plastic strips.Discoloration in some areas of the plastic strips.Tearing was observed.

Loam SoilNo physical change observed

No physical change observed

Thinning in some portions of the plastic strips.Discoloration in some areas of the plastic strips.Tearing was observed.

Sea water No physical change observed

No physical change observed

Thinning in some portions of the plastic strips.Discoloration in some areas of the plastic strips.Tearing was observed.

Tap water No physical change observed

No physical change observed

Thinning in some portions of the plastic strips.Discoloration in some areas of the plastic strips.Tearing was observed.

Summary of Results:

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Weight loss was observed after about two months exposure to different soil and water medium. Percent weight loss ranged from 0.09% to 30.28%. Weight loss was higher in plastic strips submerged in seawater and compost soil. This was followed by weight loss in plastic strips submerged in loam soil. Weight loss was lowest for plastic strips submerged in tap water. Mean weight loss for all was plastic strips was 12.63% (Table 1).

No physical changes were observed in all plastic strips on September 24, 2008, 16 days after exposure to different substrates. Likewise, no physical changes were observed on the plastic strips on October 26, 2008, after 28 days of exposure. On November 15, 2008, after 68 days of exposure to the different substrates, physical changes were observed in all plastic strips. Some plastic strips have small holes. Other portions of the strips have thinned out, while some showed discoloration (Table 2, Plates 7, 8, and 9).

Results showed that after about two months exposure to loam soil, compost soil, seawater and tap water, the SM plastic strips manifested signs of degradation such as weight loss, changes in physical appearance like tearing, thinning and discoloration. However, it is too early to tell whether the degradation observed are due to physical and chemical factors such as temperature, moisture, and enzymatic reactions, or these are due to the action of microorganisms like bacteria (biodegradation).

After observing the physical changes and measuring the dry weight of the plastic strips, these were again returned to the different treatment substrates for further observations.