C. Amaneesh, Hee-Sik Kim, Rishiram Ramanan 

Microplastics (MP) have received worldwide attention in recent years because of its prevalence in key ecosystems, including agroecosystems. Occurrence of MP in native paddy fields, which are critical to world’s food security, is not reported till date. This study reports the abundance of MP in two different rice cultivars, one of which is the ‘Pokkali’ crop that is Geographical Indication tagged and is a salt-tolerant, climate-resilent variety in Kerala, India. Major MP detected in this study which was conducted in the surface water layer of paddy fields during vegetative season (transplantation) and ripening season (near harvesting) were polyethylene (PE) and polypropylene (PP). MP density in vegetative phase was more than twice the ripening phase concentrations in the tested rice cultivars. Influx of monsoon rains bringing plastic runoff and soil tilling might be the potential causes. Subsequently, impacts of MP and plastic leachates (PL) on phytoplankton which are naturally found in the rice fields were examined. Microalga, Chlorococcum sp., isolated from the paddy land, and cyanobacterium, Synechococcus sp. were tested with environmentally relevant concentrations of PE-MP and PE-PL. MP bestowed a significant hormetic effect on the specific growth rate of the microalga whereas the cyanobacterial growth was negatively impacted. Such low-dose stimulatory effect is a classic response of over-compensation to mild environmental stress in microalgae. The significantly increased catalase activity and reduced superoxide dismutase activity in the cyanobacterium corroborated the toxic impact on growth. The differential response to MP and PL stress by microalga and cyanobacterium suggests that phytoplankton and MP type and size, may play major roles in determining stress response. This study underscores the possible change in community structure and function of paddy field phytoplankton at presently prevalent environmental MP concentrations and, consequently, on rice productivity.