Testes de toxicidade com sementes como ferramenta na avaliação da poluição do solo em lixões: o caso do lixão de Crateús-CE

Abstract

Urban Solid Waste (MSW) is generated by human activities and can be in solid, semi-solid or gaseous state. In 2022, according to a report by the Brazilian Association of Public Cleaning and Special Waste Companies, 81.8 million tons were generated annually, while in 2021, 29.7 million tons of waste were sent to landfills still operating in the country. Leachate contamination is one of the major impacts caused by controlled dumps and landfills. The leachate produced by MSW has varied physical, chemical and biological characteristics, making it a challenge to assess its impacts on ecosystems. Ecotoxicological tests are an important tool for monitoring and assessing risks to environmental health. Therefore, the present study aims to evaluate the phytotoxic effects of soil elutriate from the Crate˙s landfill using Allium cepa L. and Brassica juncea L. as bioindicators, determine the most sensitive toxicity parameters for evaluating soil contamination by leachate and sensitivity of seeds; determine the most toxic sampling point from phytotoxic tests. To obtain the elutriate, the soil was collected from 5 different points at a depth of 20 to 30 centimeters, solubilized with distilled water in a 1:4 ratio, shaken and decanted for 1 hour. The bioassay used 10 seeds of each species arranged in 90 mm Petri dishes with filter paper as substrate and moistened with 4 ml of elutriate. The plates were stored at a temperature of 25±2 ºC, and a photoperiod of 12:12h (light:dark) during the exposure period of 96 and 120 hours. The test was performed in triplicate for each point. After the period of exposure, measurement and counting of seeds, roots and hypocotyls, it was observed that A. cepa seeds showed a lower germination average for point 5, equivalent to 37% average germinated seed. The same point presented a moderate IER and an inhibition of 68.46 and 67.46% in root growth compared to the two controls P0 and P6 respectively. The seeds of B. juncea presented, for points 1, 2 and 3, lower GI, yet only point 3 showed a moderate IER for the control with water, while for the soil control all points, except point 1 that showed a hormesis effect, had a high IER. It was possible to conclude that the IG and IER parameters were more sensitive in determining elutriate toxicity, the B. juncea seed was the seed with the greatest sensitivity and points 3 and 5 were those that exhibited greater toxicity compared to the others.