Introduction

Have you ever seen small chalk-like colourful balls lying in a corner of your grandparents' home? Remember when you tried to pick up that curious little 'sweet', only to be stopped by your parents or an older folk? Perhaps you have been told about the dangers of touching those colourful balls. Here, we would like to give a more detailed explanation as to why those balls are harmful. We hope you stay and enjoy the read!

Those colourful balls are: MOTHBALLS.

They are placed in cupboards and wardrobes to keep away moths that would feed on clothes. Moths died immediately because mothballs contained substances that were toxic to them. Humans thought it only killed moths. However, we discover that the toxic substances have a considerable effect on humans too.

What are the active ingredients in mothballs?

-naphthalene (we will concentrate on this)

-paradichlorobenzene

These two can sublimate (change from solid to gas) and emit gasses that irritate the eyes and lungs. When inhaled, it can cause headaches, dizziness and nausea. Naphthalene can also cause red blood cells to break apart, resulting in hemolytic anaemia.

On top of all these, naphthalene can be absorbed by the skin and possibly enter the bloodstream. If the amount of naphthalene is high enough, it can cross the placenta and cause fetal toxicity.

What exactly is naphthalene?

Naphthalene is a white solid with a polycyclic aromatic hydrocarbon composed of two fused benzene rings.

 

Most of the naphthalene entering the environment is released directly to the air from sources such as burning of fossil fuels and use of naphthalene-containing mothballs. Other sources include urban air pollution and cigarette smoke.

Current Available Methods

1) Gas chromatograph (GC) is a type of chromatography used for separating and analysing compounds that can be vaporise without chemical decomposition. It can be used for the detection of naphthalene in mothballs.  Helium was used as the carrier gas at a constant inlet pressure of 70 kPa.

2) High Performance liquid chromatography (HPLC) is a form of chromatography to separate compounds that are dissolved in solution. Compounds are separated by injecting the sample of mixture into column. The different components in the mixture pass through the column at different rates due to differences in their interaction with the stationary phase. This method can also be used for the detection of naphthalene in samples. 

Selected analysis method:  Gas chromatograph (GC) with Mass Selective Detector (MSD). GC is a method that we are more familiar with. Small amounts of samples are sufficient for analysis. Tentative identification can be made with the retention time matching of the sample with standards of naphthalene. Some researchers have also favoured GC as the method best suited for the rapid analysis and have conducted the experiment with it. This is because capillary columns is used allowing a higher carrier gas flow rate, thus less resistance in an open tubular capillary columns, resulting in less back pressure and fast analysis. Also MSD is used which enhance its capability to confirm identities of compound.

Materials & Methods

Gas chromatography

Agilent model 5890 gas chromatograph equipped with Agilent model 5971A mass-selective detector operating in electron impact mode (70 eV)

Column used:  30 m × 0.25 mm × 0.25 µm HP1-MS column

Split/Splitless injector: Split injector

Injector temperature: 250°C

Oven temperature:  Programmed from 50°C to 110°C (At 2°C /min.)

Mobile phase used: Helium

Materials

Moth repellent balls

Toluene (used as the extracting solvent) from Fisher Scientific

Standards of naphthalene from UCB

Cotton cloth

Vials

Cabinet (109cm X 90cm X 34cm)

Reagent preparation

1) Standard preparation

- Prepared by using the known standard solution of naphthalene.

2) Sample preparation

The exposure period for all cloth strips was 120 h.

- During the experiments, the room temperature was kept constant at 22 °C during morning and afternoon hours, but was allowed to drop to 18 °C at night.

- The room was kept closed during the exposure to keep the conditions constant.

- Each cloth was analyzed separately after the exposure period.

Direct transfer of moth repellent to clothing

Downward migration of the repellent agent

1) A moth repellent ball was placed directly on ten layers of cotton cloth (4 × 4 cm) (cotton is the most often used type of fabric.)

2) Pieces measuring 4 × 4 cm were analyzed using ultrasonic extraction followed by GC–MS analysis.

Ultrasonic bath

3) The cloth pieces were placed in vials containing 5 ml of toluene and extracted in an ultrasonic bath for 15 min prior to gas chromatographic analysis.

4)  All experiments were repeated three times and mean values were calculated.

5) Analyte concentrations in the extracts were calculated from external calibration graphs determined using 1:10 split injection.

Horizontal migration of the repellent agent

1) A moth repellent ball on a strip of cloth (4 × 60 cm), which was cut after the exposure into seven sections (4 cm in length, centered at 2, 6, 14, 28, 36, 44 and 55 cm.)

2) These strips were analyzed using ultrasonic extraction followed by GC–MS analysis

3) The cloth pieces were placed in vials containing 5 ml of toluene and extracted in an ultrasonic bath for 15 min prior to gas chromatographic analysis.

4) All experiments were repeated three times and mean values were calculated.

5) Analyte concentrations in the extracts were calculated from external calibration graphs determined using 1:10 split injection.

2) Indirect transfer of moth repellents to clothing

1) Pieces of cloth were placed on all three shelves in the cabinet-109 cm in height, 90 cm in length and 34 cm in width. (lower, middle and upper).  

2) Mothball repellent tablet was placed on the middle shelf.

3) One piece of cloth, placed on the shelf with mothball, was exposed to air for one-hour prior to extraction and analysis. The other pieces were extracted and analyzed immediately after exposure.

3) The cloth pieces were placed in vials containing 5 ml of toluene and extracted in an ultrasonic bath for 15 min prior to gas chromatographic analysis.

4) All experiments were repeated three times and mean values were calculated.

5) Analyte concentrations in the extracts were calculated from external calibration graphs determined using 1:10 split injection.

Risk Assessment

Department: LSCT 

Process: Gas Chromatograph (GC) with Mass Selective (MS) detector 

Results

In all cases, relative standard deviations did not exceed 10% and R² values were higher than 0.998. The purity of the moth repellent tablets was examined by comparing the response to that of a known standard solution. All tablets were found to be nearly 100% pure. Quantitation was based on extracted ions of m/z 128 naphthalene.

Fig. 1. Results of downward migrations of mothball repellent agents. Analyte concentration vs. the number of the cloth layer in the stack for the moth repellent agents

The concentration of the naphthalene remained nearly constant (at 150µg/g) throughout the stack with the exception of the top layer. This indicates that naphthalene approached equilibrium by saturating or nearly saturating the cloths in the stack. Therefore, naphthalene found in mothball can be transferred onto the clothes.

Fig. 2.Horizontal migration of the moth repellent agents

The concentration distribution decrease exponentially with distance from the position of the mothballs.  However, the concentration of the naphthalene released from mothballs can still be felt at a distance of 60cm.

Fig. 3. Indirect transfer experiments with the moth repellent agents

Naphthalene vapors are heavier than air. Thus,the observed concentration distributions is due the density of the chemicals in relation to that of the air. Concentration of naphthalene on the lower shelf is higher than on the upper shelf. The largest analyte concentration was found on the cotton cloths placed on the middle shelf, containing the mothball. As the shelves act as obstacles hindering vapor transport between the individual compartments defined by the shelves. As a result, the cloths placed on the middle shelf were exposed to moth repellent vapors for the longest time and adsorbed the largest amounts of the analytes.

Fig. 4.  Indirect transfer of the analytes to cloths placed on the middle shelf, with and without airing.

Airing the cloths for one-hour lowered the concentration of the repellent in the cloths. However, the residual concentration of the repellent agent was still high after this time. The results obtained indicate that one-hour airing is insufficient to significantly lower the concentration of the moth repellents.

Discussion & Conclusion

Although they are immensely potent at keeping moths away from feeding on our clothes, mothballs are becoming less popular as more people learn of the harm it can cause us. Naphthalene residues are now proven to be transferable from pellet to clothes in direct contact. It can also travel through a few layers of clothing. If it can move from layer to layer, our skin would be no exception when wearing these clothes. 

Another finding was that naphthalene vapours linger at lower areas of the cupboard due to a higher density. This means that clothes placed at the bottom of cupboards would soak up the most naphthalene. Lastly, we discovered that even after airing the clothes for some time before wearing, the clothes still had one-third of the original naphthalene concentration in them. 

These analyses, achieved through Gas Chromatography coupled with a Mass Selective Detector, too strongly suggest that naphthalene residues are not easily removed from clothes. And unless the clothes are washed before wearing, naphthalene would undoubtedly get onto the skin and silently cause harm.