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Effects of Downy Care Fabric Softener on Brassica rapa

Tim Austin, Angela James, and Andrew Kniss


Abstract: The effects of Downy Care fabric softener on Brassica rapa were tested using a completely randomized design. The plants were grown in artificial soil with no fertilizer using Wisconsin fast plant hydroponics under fluorescent light. Varying numbers of drops, at approximately 1.0 ml each, were added to the soil to test the phytotoxicity and it was found that increasing amounts of fabric softener were inhibitory to growth. The fabric softner was tested to determine its ingredients and was found to contain high levels of sodium, which were the probable cause of growth inhibition.
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Introduction

Wisconsin Fast Plants, Brassica rapa or Rapid Cycling Brassicas (RCBr) are in the family Brassicaceae. Related agricultural species include, turnips, cabbage, and pak choi. Brassica rapa or B. campestris was originally a wild mustard weed species. The University of Wisconsin developed and bred the wild plant for use as an education tool for teaching plant biology. Because of their small size and rapid life cycle, biological plant research can be conducted on the plants in a limited amount of space, over a period of four to eight weeks and without expensive special equipment. Experiments frequently conducted on RCBr include genetics, ecology, plant growth, and phytotoxicity or phytoremediation (Green 1989). In this experiment, the affects on the growth of B. rapa plants, from small amounts of Downey Care fabric softner, were studied.

Downy Care fabric softener, produced by Proctor & Gamble, lists its ingredients as being cationic and states that it is biodegradable(1). Due to the state of the environment, consumers feel better about buying products that are biodegradable. However, even though a product is biodegradable, it is not necessarily safe for the environment. For years, detergents and fabric softeners have contained phosphorus, which enhanced plant growth, but phosphorus buildup in the soil and water has begun to cause environmental problems. For this reason, companies were forced by law to change the ingredients in their products but were not required to list ingredients of the product. Because the ingredients for Downy Care were unlisted, the effects of the fabric softener were tested on Brassica rapa, and the expectation was that addition of fabric softener to the soil might enhance growth of B. rapa similar to other biologically safe products previously tested on brassicas.


(1) Manufacturer's label. - this footnote would go at the bottom of the page on which the reference occurred.

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Materials and Methods

The approved Wisconsin fast plant hydroponics set up was used, as described in the Fast Plant Manual Growing instructions (Green, 1989). Five seeds of the Brassica rapa plant were used in each treatment canister using an artificial soil mix containing 50% growth media and 50% vermiculite. No fertilizer pellets were added in the experiment. The plants were grown eight inches from fluorescent lights. All treatments were monitored weekly and watered as needed.

Varying numbers of drops of Downey Care fabric softener were added before the seeds were planted. The drops were added at rates of zero, six, twelve, eighteen and twenty-four drops for corresponding treatments. The experiment used a completely randomized design with one control and four treatment levels. Plants were harvested three weeks after the planting date of September 18, 1998. At harvest, plants were counted and wet weights for each individual canister were taken. Three weeks later dry weights for each replicate of the treatments were taken and recorded.

Dry weight data was statistically analyzed using the Statistical Analysis System (SAS) program at the University of Wyoming. The null hypothesis was that Downy Care would not affect the growth of Brassica rapa plants. The alternate hypothesis was that Downy Care would have an affect on Brassica rapa plant growth.

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Results and Discussion

Statistical analysis of the data showed that there were no significant differences between the control and the treatment of 6 drops of Downy Care. There were also no significant differences found between the treatments of 12 drops, 18 drops, and 24 drops of Downy Care. However, there was a significant difference between the control, and the treatments of 12, 18, and 24 drops of Downy Care. There was also a significant difference between the 6 drop treatment and the other three treatments, since for our analysis there is no difference between the control and the 6 drop treatment. From this point the control group and the 6 drop treatment will be referred to as group A, and the 12, 18, and 24 drop treatments will be referred to as group B. Group A exhibited significantly more growth than group B, so the null hypothesis was rejected in favor of the alternate hypothesis that Downy Care would cause a difference in growth. Table 1.0 shows the replicate means and the treatment means for the experiment.

The analysis showed that the F value was 14.99, and the probability of getting a greater F value was 0.0001 which is less than our selected 0.05 value for alpha, so the null hypothesis was rejected in favor of the alternate hypothesis. Figure 1.0 shows the treatment means graphed linearly. It can be concluded that Downy Care fabric softener has a phytotoxic effect on Brassica rapa at or above a level of 12 drops. The sample data for this experiment was not normally distributed, and transformations were not done.

The null hypothesis, that addition of Downy Care would have no effect on growth, was rejected in favor of the alternate hypothesis, that the Downy Care would cause a difference in growth. Since the cause of the growth decrease was unknown, the fabric softener was tested to determine the possible cause. The test showed that Downy Care fabric softener contained 288.82 MEQ/L sodium, 114.07 MEQ/L calcium and also had a Sodium Adsorptive Ratio (SAR) of 54.09.

Sodium, through many experiments, has been found to be phytotoxic at high levels. Tests show higher SAR levels affected growth of Brassica napus and found that at SAR levels above 20, the stem growth and yield were significantly reduced and at SAR levels over 34, stem number and seed production were also decreased. These findings show that at an SAR level of 54.09, as was found in the fabric softener, plant growth would be greatly inhibited and possibly even prevented. (Gutierrez, et.al.1996)


In an experiment conducted by Singh, it was found that higher salt concentrations reduced germination of five different vaieties of Brassica campestris (Singh 1992). Two additional experiments showed the effects of salinity on plants. The first showed that the potassium/sodium ratio in six rapid-cycling Brassica species was reduced greatly due to seawater salinity, and the decrease was attributed to salt-induced growth reduction. The second showed that factors such as the Relative Growth Rate (RGR), Net Assimilation Rate (NAR), and Leaf Area Ratio (LAR) of Brassica carinata were all reduced in the early stages of growth due to salinization. The NAR reduced mostly due to the reduced RGR, but because of the reduced NAR, concentrations of nutrients in the plant tissues, such as potassium and calcium were decreased and concentrations of sodium, magnesium, and chlorine were all increased (He and Cramer 1993).

Studies that show that sodium is phytotoxic to Brassica are easy to find and relatively conclusive. Due to the high level of sodium found in Downy Care fabric softener, the cause for growth inhibition of Brassica rapa is obvious. Proctor and Gamble changed the composition of their fabric softener and it no longer contains phosphorus, which is environmentally conscentious. However, the phosphorus was replaced with sodium, which is phytotoxic in high levels and is not environmentally safe. Instead of being a water pollutant that enhances plant growth, Downy Care fabric softener is now a toxic substance that kills vegetation and pollutes the environment.

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Literature Cited

Green, R.P. 1989. Wisconsin Fast Plant Growing Instructions. Carolina Biological Supply Co. pp. 3-14.

Gutierrez Boem, F.H. and Lavado, R.S. 1996. The effects of soil sodicity on emergence, growth, development and yield of oilseed rape (Brassica napus). Journal of Agricultural Science. 126: 169-173.

He, T. and Cramer, G.R. 1993. Salt tolerance of rapid-cycling Brassica species in relation to potassium/sodium ratio and selectivity at the whole plant and callus levels. Journal of Plant Nutrition. 16: 1263-1277.

He, T. and Cramer, G.R. 1993. Growth and ion accumulation of two rapid-cycling Brassica species differing in salt tolerance. Plant and Soil. 153: 19-31.

Singh, A.K. 1992. Seed germination of Brassica campestris. Indian Botanical Contractor. 9: 159-163.