Effects of Conventional and Eco-Labelled Laundry Detergents on Water pH and Dissolved Oxygen

Thomas Chen1, Wilson Li1, Alvin Sheng1  (1Case study, Spring 2026)

01
Introduction

Laundry water carries surfactants and builders into municipal systems and eventually into rivers and coastal water, where they are reported to stress aquatic organisms even at low concentrations.1

“Eco-friendly” is a marketing phrase rather than a regulated one, and shoppers have no simple way to verify it. This study asks whether an eco label corresponds to a measurably gentler effect on water.

02
Objectives
  • Measure how four laundry detergents change water pH and dissolved oxygen (DO) over a fixed window.
  • Compare eco-labelled products against conventional ones on the same two indicators.
  • Separate detergent effects from background drift using an untreated control.
03
Methods
  • Prepared five identical water samples, each starting at pH 7.0.
  • Dosed four samples with an equal amount of one detergent each; the fifth was left untreated as a control.
  • Recorded baseline pH and DO at t = 0.
  • Re-measured both indicators every 10 minutes for 50 minutes.
  • Compared each sample against the control over the same window.

Table 1. Detergents tested and their marketed category.

SampleCategory
Eco MaxEco-friendly
Old DutchEco-friendly
Kirkland UltracleanConventional
Tide UltracleanConventional
WaterUntreated control
04
Results

Acidity

Every detergent pushed the water alkaline within the first 10 minutes and then held steady. The two eco-labelled products settled roughly a full pH unit above the conventional pair, while the control stayed near neutral.

6.8 7.0 7.4 7.8 8.2 8.6 8.9 0 10 20 30 40 50 Eco Max Old Dutch Kirkland Tide Water (control) Time (min) pH

Figure 1. pH of each sample over 50 minutes, recorded at 10-minute intervals.

Dissolved oxygen

All four detergents lowered DO steadily from the same 8.85 mg/L baseline, with no sign of levelling off by 50 minutes. The ordering reverses here: the conventional detergents stripped the most oxygen and Old Dutch the least.

8.0 8.2 8.4 8.6 8.8 0 10 20 30 40 50 Eco Max Old Dutch Kirkland Tide Water (control) Time (min) Dissolved oxygen (mg/L)

Figure 2. Dissolved oxygen concentration over the same window.

05
Conclusions

Table 2. Net change in pH and dissolved oxygen after 50 minutes.

SampleΔ pHΔ DO (mg/L)
Old Dutch+1.70−0.30
Eco Max+1.68−0.45
Tide Ultraclean+0.76−0.75
Kirkland Ultraclean+0.72−0.65
Water (control)−0.08−0.05

Every detergent raised pH and lowered DO while the control barely moved, so the shifts are attributable to the products rather than to the water or the handling.

The eco label did not predict a gentler result. It predicted a larger pH shift and only a slightly smaller oxygen loss.

06
Discussion

Interpretation

The result contradicts our hypothesis. One untested explanation is that pH tracks the alkaline builders used for cleaning power rather than surfactant toxicity.

Limitations and next steps

pH and DO indicate change, not harm, and a single trial in a beaker cannot account for dilution or biodegradation in a river. Replicates, a longer observation window, and tests of individual ingredients rather than whole formulas would sharpen the comparison.2

References

  1. Effects of detergents and surfactants on aquatic organisms. PubMed Central. https://pmc.ncbi.nlm.nih.gov/articles/PMC12035000/
  2. Impact of surfactants on marine ecosystems. International Research Journal of Environmental Sciences, 3(8). https://www.isca.me/IJENS/Archive/v3/i8/1.ISCA-IRJEvS-2013-210.pdf