Effect of disinfectants used as floor cleaners on the growth of plants

Does the growth of mung beans (Vigna radiate), measured in terms of seed vigour index depends on the concentration (measured in terms of volume percentage) of commonly used disinfectants – Lysol and Dettol exposed to the seeds?

Being an inquirer, observing phenomena and using my scientific knowledge and principles to analyze or explain them are my forte. The idea of the current investigation originates from a daily life observation. It was unfortunate to note that the potted plants in the small garden on our terrace were dying all of a sudden. While trying to find the reason behind this, it was found that our maid was disposing the unused water used for mopping floors on them. To delve further, it came to my mind that it may be the floor cleaners which she mixed in the water which may have caused these plants to die. Floor cleaners are disinfectants dissolved in alcohols. Most of them contain ammonia solution and are usually acidic in nature. They are mainly used to kill germs and bacteria on the floor and remove stains. When plants are exposed to them, various metabolic processes in them like synthesis of chlorophyll, water uptake by root hair cells, germination of seeds are disturbed. The chemical composition of floor cleaners depends on the type of it and thus the effect will vary too. The focus of this investigation is to understand is two -fold; firstly to understand that whether the percentage concentration of floor cleaner used has any effect on the growth parameters of plant or not; secondly to understand if there is any significant difference between the effect that a floor cleaner has on the plant and the type of it. We use a lot of household chemicals everyday for various purposes and most of them are either surfactants or ammonia based. But how do we dispose them? Do we follow any customized safe disposal method? In most cases, we do not as we just simply dump them into the drainage system which seeps into the water that plants use. In this way, disposal of household chemicals has been a major reason of water pollution and has a detrimental effect on the ecosystem. The relevance of the current investigation lies in the fact that how this sort of water pollution are affecting the growth of plants.

Mung beans(Vigna radiate ) are one of the essential part of daily nutrition and is a chief source of protein for vegetarian diet. It is used to obtain sprouts. Although, India is the main source of these plants yet now it is available in various parts of UK. It is a kind of legume belonging to the„ Fabaceae‟ group. It is a plant with an annual life span. This plant can grow vertically maximum up to 1.0 m of height . There are various reasons behind choosing this seeds for the investigation which mainly are -

• The seeds are cheap and easily available in the local super market. 
• The germination of these seeds and their growth as well do not require any extreme conditions.
• The results obtained from these seeds are quite reliable. 
• The germination of seeds does not need any feeding as such. 
• Average temperature condition is good enough for the germination of seeds.

Measuring seed vigour is a useful tool to understand or get an insight about the germination or growth of seeds before it is sown into the field. As there are lot of physic-chemical factors playing a role in this process, a standard definition of seed vigour was given by ISTA Congress in 1977 as – “the sum total of those properties of the seed which determine the level of activity and performance of the seed or seed lot during germination and seedling emergence”. Higher the value of seed vigour index, more the growth of the plant.

It is usually calculated according to the formulagiven below -

Seed Vigour Index (SVI) = [G%  R] + SR .............................. (equation 1)

\(G\% = \text{Germination percentage} = \frac{number\ of\ seeds\ germinated}{total \ number\ of \ seeds}\)

R = Length of root in cm

SR = number of secondary roots

Floor cleaners are mainly disinfectants dissolved in alcohols. They can affect the growth of plants in multiple ways - Floor cleaners contain detergents or surface active reagents. They have the ability to solubilise the waxy cuticle in leaves. Absence of waxy cuticles in leaves may cause the leave to dry and also reduces the heat tolerance of it. Detergents can also interfere with the water absorption by root hair cells as if water containing detergents dissolved in it are absorbed by root, it may destroy the lipid membrane of the root hair cells and that will inhibit the uptake of water and nutrients from soil which may cause the plant to die. Water soluble ionic salts are also part of the composition of the floor cleaners. Once it is mixed with the water, the osmotic pressure of the water rises and thus the water absorption of the root process of absorption of water from soil by root hair cells might slow down which will again dehydrate the plant and inhibit various metabolic functions in it. Floor cleaners are mostly acidic in nature. Presence of such acidic substances in the water exposed to plants will lower down the pH of the soil in which the plant grows and makes the soil unsuitable for growth of the plant.

Lysol is a popular disinfectant manufactured by the company Reckitt Benckiser. It is mainly composed of antiseptics like – lactic acid, 4-chloro-2-benzyl hydroxybenzene, dimethyl benzyl ammonium chloride dissolved in ethanol and propan-2-ol as solvents. It also contains trace amount of hydrogen peroxide. The most active ingredient of Dettol is chloroxylenol which acts as an insecticide and has anti bacterial properties. Castor oil, pine oil, ethanol and castor oil are used as solvent in it. Trace amount of surfactants like SDS (Sodium do decyl sulphate) are also found in it.

A research article titled – “The Effects of Household Chemicals on Household Plants” by Amy Hall, John Wood, Chris Kolososki and Matt Howell can be considered as a relevant literature reference for this investigation. It was based on a study of the effect of different brands on glass cleaners and soaps on different variety of seeds. As mentioned in the abstract it was clearly noted that – “The plants that are receiving chemicals appear to growing at a noticeably slower rate than the control plants, and more of them are dying”.

Null hypothesis
Commonly used floor cleaners – Lysol and Dettol has no effect on the growth of Mung beans.

Alternate hypothesis
Commonly used floor cleaners – Lysol and Dettol have a negative impact on the growth of Mung beans. As the % concentration of floor cleaners increases, the seed vigour index decreases.

There are two independent variables in this investigation-

Brand of floor cleaner used-
Lysol and Dettol. These two brands are chosen as these two are the most commonly used floor cleaners. Moreover, Lysol is ammonia based alkaline disinfectant while dettol is not. This would enable us to investigate the effect of ammonia as well as alkalinity on the growth of plants.

% concentration of floor cleaner used –
The % concentration (volume %) of floor cleaner used was varied by adding the floor cleaner using a graduated pipette to 100 cm³ of tap water. The values of concentration chosen were – 1.00%, 2.00%, 3.00%, 4.00%,5.00%, 6.00%, 7.00%,8.00%, 9.00% and 10.00%. The values of concentration are chosen within this range as the recommended dosages¹⁰ of the floor cleaners lies in the range of 1.00% to 10.00%.

The dependent variable of the investigation is the seed vigour index. Growth of a plant can be measured can be measured in various aspects – root length, germination %, shoot length, number of leaves, chlorophyll content and many more. Seed vigour index is a standard protocol to monitor the growth as well as to understand the feasibility of crops grown as already discussed in the background information. The seed vigour index will be calculated using the equation -1 (refer to Page 2).

Protective clothings like safety masks, safety gloves and lab coats were used as exposure of the floor cleaners used and inhalation of their vapors may cause nausea and vomiting. None of the materials used were ingested or inhaled as consuming them may cause toxic health effects like respiratory disorders, cardiac disorders.

Minimum amount of seeds were used. Any methodology that might give rise to any undesirable ethical issues were not entertained.

All waste and unused materials were diluted by adding tap water and disposed off safely into the waste bin.

A 10.00 % solution of Lysol was made by adding 10.00 ± 0.05 cm³ (using a graduated pipette) of Lysol to 90.00 cm³ of tap water (using a graduated measuring cylinder) in a 100 cm³ glass beaker. 1.00 ±0.05 cm³ of this stock solution was added to 9.00 ± 0.05 cm³ of tap water in a test tube to prepare 1.00 % of the Lysol solution. Similarly 2.00%, 3.00%, 4.00%, 5.00%,6.00%, 7.00%, 8.00% and 9.00% solutions were prepared by using 2.00 cm³ , 3.00 cm³ , 4.00 cm³ , 5.00 cm³ , 6.00 cm³ , 7.00 cm³ , 8.00 cm³ and 9.00 cm³ of the stock solution to 8.00cm³ , 7.00 cm³ , 6.00 cm³ , 5.00 cm ³ , 4.00 cm³ , 3.00 cm³ , 2.00 cm³ and 1.00 cm³ of tap water. The Dettol solutions were prepared in the same way. All the test tubes were labelled using a permanent marker and kept on the test tube stand. A 10.00 cm³ graduated pipette was used to add both the stock solution and tap water.

A petri dishes were taken and washed with 1% solutions of NaOCl and dried in air. Two filter papers were kept on the dish. 2.00 ± 0.05 cm³ of tap water was added to it using a graduated pipette. Ten seeds were kept in them. The seeds were allowed to germinate for 1 day. Next day, the number of seeds germinated (out of 10 ) were counted and noted down. Then, the seed was allowed to grow for 7 days and after 7 days, the root length was measured using a ruler in cm and the number of secondary roots was counted. This was taken as a control and the same procedure was used for all other % of both Lysol and Dettol- 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, 6.00%, 7.00%, 8.00%, 9.00% and 10.00% (stock solution). In total, 21 (10 for Lysol, 10 for Dettol and 1 for control ) petri dishes and 210 ( 10 seeds in each of the 21 petri dish) seeds were used. All the petri dishes were placed near a window sill so that they receive optimum sunlight.

• A tiny root of pinkish white colour emerged from the seed after 1 day. 
• More number of seeds were germinated in the control petri dish in comparison to the ones with Lysol and Dettol.
• Trace amount of shoot development was noted in the direction of light with tiny leaves of light green colour.
• The roots were growing at a faster rate than the shoots.