Plastic laboratory materials are found to affect vital parameters of the waterflea Daphnia magna. The main responsible factor is defined as "newness" of the materials. Juvenile D. magna were raised individually in; a) new laboratory-standard 50 ml polypropylene tubes, and; b) identical tubes which had been washed and aerated for several weeks. Newness had significant effects on growth and fecundity of D. magna. New tubes caused delayed maturation, reduced reproduction and reduced growth when compared to washed and re-used tubes of the same commercial brand. The findings indicate that newness of tubes has inhibiting or toxic effects on D. magna. Often laboratory plastics are intended for single-use due to sterility demands. Newness might be an important confounding factor in research results and should not be disregarded. Disposable plastic utensils may come with a seemingly ignored cost and induce adverse effects in biological test-organisms and systems. The presented findings accentuate continued need for general awareness concerning confounding factors stemming from material laboratory environment. Based on the present findings the authors suggest that plastics intended for use in sensitive research may need to be washed and aerated prior to use.