Abstract:
There is much concern about the hazardous effects of hand washing products on the
environment due to their increased use during the Covid-19 pandemic. Even though
these products have been released into streams for several years, their fate and behaviour
are not well known yet. This study aimed to evaluate the impact of four regularly
used handwashing liquids in the Sri Lankan market on freshwater algae. Chlorella
vulgaris, the test organism, was grown in the OECD medium amended with four selected
concentrations (0.50, 1.00, 1.50, and 2.00 mL/L) of four liquid handwashes, and a control
sample was maintained without adding handwash. An inoculum of Chlorella vulgaris
was added to each test concentration to obtain 105 CFU/mL initial algal count. The
growth of Chlorella vulgaris was detected using the optical density measurements at 430
nm in quintuplicate. The procedure was repeated at 24-hour intervals for one week and
at 72-hour intervals until 21 days. The relative growth of test samples based on optical
density was calculated as a percentage in comparison to the untreated control, and
the effect of each hand wash on algae was determined in terms of percentage survival.
According to the graphical interpretation of the results, survival percentages drop as
handwash concentration rises, but surprisingly, they rise at 1.50 ml/L in three products.
The repeated measures ANOVA technique is used to analyse the effect of handwash
concentration and the interactive effect of concentration and time on algal growth.
According to the statistics, there are no significant differences in the growth when
increasing the concentration of three products (p < 0.05). However, growth has increased
when increasing the concentration only in one product, and the growth has increased
with time (p < 0.05) in all products. It can be concluded that liquid handwashes affect
the growth of freshwater algae in either a positive or negative manner. This may be due
to the collective effect of constituents of the handwashes tested.
