Tocantins is located on an agricultural border, an area that converts natural habitats
to agriculture, which makes this region susceptible to environmental impacts, which can affect
the enormous biodiversity that is characteristic of the region. These frontiers are concentrated
today in environments that are beginning to suffer the effect of land management and its harms,
such as the use of pesticides and fertilizers. In this work, chemical contaminants (pesticides,
metals), bioindicators and physical chemical parameters were investigated in water, soil and
sediment of the Rio Formoso, in the State of Tocantins, in the region of influence of the Rio
Formoso agricultural project. Four quarterly collections were made (2018 to 2019), covering
the dry and rainy periods in the region. One point was sampled on the river, before it passed
through the agricultural project (P1) 25 km before the start of the project region, 5 points along
the project (P2 to P6) and one point after the river passed the project's margin ( P7), making 45
km from P2 to P7. The quantified and / or detected pesticides were mostly present in the water
samples (21 active ingredients), and some in the soil (4 active ingredients). No pesticides were
detected in the sediment. It was found that the driest periods are the most critical, there is less
dilution and therefore a higher concentration of substances. However, at low concentrations in
water, the substances found may be able to cause harmful effects in some species due to their
high toxicity, since the effects of a pesticide, can be enhanced in the presence of others
(synergy), or cause cumulative effects. . Although the waters of the Rio Formoso were already
contaminated even before passing the margins of the Rio Formoso Project (P1), mainly with
atrazine and clomazone, this contamination is aggravated by the appearance of other substances
on the margins of the project, such as ametrine, carbendanzim, fluazafope , imazetapyr,
methylsulfuron, simazine, tebuconazole and tricyclazole, which were found in the waters of the
Rio Formoso, only between points P2 to P7, (points on the margins of the agricultural project).
This behavior is an indication that the contamination by these substances, in this environmental
compartment, is due to local agricultural activities, and the soil is also contaminated at points
P4 and P5. The analysis of the physical-chemical parameters in the water, indicated high levels
of total phosphorus and low levels of dissolved oxygen, although the Water Quality Index
showed good water quality in the monitored period. The amounts of metals were below the values of the legislation. Because there are no values of backgrounds in the region, for metals,
its presence cannot be attributed to the project. Multivariate statistical analysis and main
components indicated that the river's behavior differs in the dry and rainy period, indicating the
need for monitoring in these two distinct periods. The Family Biotic Index indicated organic
contamination in the waters of the Rio Formoso, which was confirmed by the analysis of
pesticides, as well as showing a better biological quality of benthic organisms in P1. With this,
it can be concluded that there is a real impact of the agricultural activities of this project, in the
quality of the aquatic environments of the Rio Formoso.
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