The comparison effect on earthworms between conventional and biodegradable microplastics

Abstract

Many studies have reported the toxic effects of microplastics (MPs) on organisms, especially on how conventional plastics affect organisms after short-term exposure. The effects of biodegradable plastics on organisms are, however, largely unexplored, especially concerning their impact after long-term exposure. We perform a series of experiments to examine the effects of conventional (polyethylene (PE)) and biodegradable (polylactic acid (PLA)) microplastics on earthworms at three concentrations (0.5 %, 2 %, and 5 % (w/w)) and particle sizes (149, 28, and 13 μm) over short- (14 d) and long-term (28 d) periods of exposure. Negative effects on earthworms are more pronounced following exposure to PE than PLA, particularly over the shorter term. After longer-term exposure, earthworms may adapt to PE and PLA environments. A close relationship exists between the effects of MPs on earthworms and activities of superoxide dismutase, catalase, and malondialdehyde enzymes, which we use to evaluate the degree of antioxidant damage. We report both PE and PLA to negatively affect earthworms, but for the effects of PLA to be less severe after longer-term exposure. Further investigation is required to more fully assess the potential negative effects of PLA use on soil organisms in agriculture.

Keywords: Adaptation; Earthworms; Microplastic; Oxidative stress; Polyethylene; Polylactic acid.

Fig. 1

The mortality in E.fetida induced by exposure to MPs. (A) and (B) are the mortality after 14 days of exposure to PE and PLA, respectively; (C) and (D) are the mortality after 28 days of exposure to PE and PLA, respectively. Different alphabet letters indicate significant differences between treatments at the p < 0.05 level.

Fig. 2

The biomass change rate in E.fetida induced by exposure to MPs. (A) and (B) are the biomass change rate after 14 days of exposure to PE and PLA, respectively; (C) and (D) are the biomass change rate after 28 days of exposure to PE and PLA, respectively. Different alphabet letters indicate significant differences between treatments at the p < 0.05 level.

Fig. 3

The SOD level in E.fetida induced by exposure to MPs. (A) and (B) are the SOD level after 14 days of exposure to PE and PLA, respectively; (C) and (D) are the SOD level after 28 days of exposure to PE and PLA, respectively. Different alphabet letters indicate significant differences between treatments at the p < 0.05 level.

Fig. 4

The CAT level in E.fetida induced by exposure to MPs. (A) and (B) are the CAT level after 14 days of exposure to PE and PLA, respectively; (C) and (D) are the CAT level after 28 days of exposure to PE and PLA, respectively. Different alphabet letters indicate significant differences between treatments at the p < 0.05 level.

Fig. 5

The MDA level in E.fetida induced by exposure to MPs. (A) and (B) are the MDA level after 14 days of exposure to PE and PLA, respectively; (C) and (D) are the MDA level after 28 days of exposure to PE and PLA, respectively. Different alphabet letters indicate significant differences between treatments at the p < 0.05 level.