Impacto das actividades humanas no ecossistema de Palizada, Campeche, México

Abstract

The present research concerns the environmental impact of pesticides used in the Fluvio Lagoon Palizada River Subasin (FLPRS) in Campeche, Mexico on environmental health using biomarkers in wild mosquitofishes (Gambusia yucatana) and whistling ducks (Dendrocygna autumnalis), likewise in campesinos (peasants). Mosquitofishes (G. yucatana) and black-bellied whistling duck (D. autumnalis) were chosen as bioindicators as they are abundant species, the fishes in small streams of the region; and the whistling ducks (D. autumnalis) in wetlands, being most abundant in flooded savannahs and irrigated rice fields. In this work were included human been because they applied the pesticide and are exposed at the first time. The biomarkers used to asses the environmental exposures to pesticides were acetylcholinesterase (AChE, EC 3.1.1.7), glutathione-S-transferases (GST, EC 2.5.1.18) and lactate dehydrogenase (LDH, EC 1.1.1.28). In this research was evaluated the environmental impact of pesticide use in the FLPRS in order to 1) know the environmental conditions of PRS in relation to water quality and land use, 2) evaluate in laboratory the use of biomarkers such as AChE, GST and LDH in wildlife exposed to pesticides, 3) estimate with biomarkers the environmental pesticide effects on organisms from aquatic (mosquitofish, G. yucatana) and terrestrial (whistling ducks, D. autumnalis) compartments, and 4) evaluate the adverse effects of pesticides used by fieldworkers from El Juncal, Palizada using symptoms related to pesticide exposure and a biomarker. The assessing of environmental impact of pesticide was carry out with the biomarkers mentioned with a test battery in situ through a biomonitoring study and toxicity test chambers in aquatic organisms, and with a survey on brain cholinesterase biomarker in terrestrial organisms. The results of this study indicated that during the last 20 years, in the Palizada River Subasin (PRS) the land use change has been drastic mainly in agriculture cover because this increase in more than 1,000 %, and the total amount of pesticide used is parallel to this increase in agricultural hectares. The use of an index of water quality (WQI) identified that from the nine sampling sites studied in the PSR, sites with cattle ranching (WQI= 0.58) and agricultural (WQI= 0.65) activity were the sites with a significant average of WQI worse than the others sites (WQI = 0.68 – 0.73). In mosquitofish (G. yucatana), the characterization of cholinesterases seems that the main form present in both muscle and head is AChE. The ranking of in vivo toxicity (LC50) of the tested pesticides to G. yucatana was chlorpyrifos > carbofuran > glyphoste. ChE activities of muscle and head of mosquitofish were significantly inhibited by furadan after 24 hrs of exposure with an inhibition of 60% at 0.06 mg/L. The mixture chlorpyrifos/glyphosate is 34% more toxic than the chlorpyrifos tested alone. In the test with 6 chlorpyrifos, fish that survived after an exposure of 96h to concentrations between 0.006 and 0.012 mg/L showed a ChE inhibition near to 80%. Muscle and head AChE activity was inhibited by chlorpyrifos and carbofuran; gill GST was inhibited by carbofuran; and muscle LDH activity was not altered by any of pesticides tested. In the case of whistling duck (D. autumnalis), the forebrain ChE seems to be AChE. The carbofuran-chlorpyrifos mixture was the most potent in vitro inhibitor of D. autumnalis brain ChE tested. This is important because in real conditions the exposure is with a mixture of pollutants which can cause possible synergistic effects. The field study in the PRS was focused to three different sampling sites, one with cattle ranching activity, other with agricultural activity, and the last one was the Palizada River. The first phase of the in situ study demonstrated the possibility of a link between the water quality index (WQI) and the variation of abiotic conditions that may cause effects on survival, growth, and biomarkers on fishes exposed not related with direct effects of pollutants. In the biomonitoring studies using enzymatic biomarkers in wild fish present the advantage of diagnosing the real exposure and/or effects of environmental contaminants but they may underestimate the actual contamination of the water, since organisms with a reasonable degree of mobility may avoid the exposure. The results obtained in this study indicate that some water variables can influence directly or indirectly on enzymatic activity, and consider it as a natural variability of activity. The integration of information generated in situ toxicity test and wild fishes reflected a concordance between percentages of AChE activity in wild fishes and exposed in situ in the Palizada River during February, July and November. The results of the study with whistling duck (D. autumnalis) suggest that ducks are exposed to pesticides (inhibition above 30% of ChE activity), at least during the season of intensive application. The evaluation of the adverse effects of pesticides in fieldworkers from El Juncal, Palizada using AChE as a biomarker showed no conclusive results from the regression analysis of symptoms and AChE inhibition activity. Some symptoms are probably compatible with acute organophosphate and carbamate poisoning such as headache, weakness, nausea, sweating and tiredness. No differences were observed with respect to use of protective clothing. It is recommended the use of pesticide less aggressive to environment and human health, also further field studies incorporating a systematic monitoring of wild populations and investigating also population parameters are particularly important for local pesticide management.