Pesticide evaluation in water, sediment and in oyster shells (Crassostrea rhizophorae) in the Manzanillo- Niquero coastal area, Cuba

Occasionally pesticides have been used excessively for the pest control in agriculture, and many of these compounds become toxic for living organisms, including man. Adjacent lands to Guacanayabo gulf, Cuba, show an important use in agriculture, mainly in rice due to the contribution of fluvial waters from several hydrographical basins. The coastal area from Manzanillo to Niquero, Granma province, is the habitat of commercial shrimps, oysters and fish. The objective of the study was to determine in that region the presence of chemical residues from pesticides in the waters, sediments and shells of the mangrove oyster Crassostrea rhizophorae, Guilding (1828), as indicators of contamination. Samplings were carried out in maximum rainfall months. Besides samples for pesticide determination by gas chromatography, hydrology was studied, and there were carried out surveys (85 farmers) to know about pesticide types, dose and application frequency per crop, for conceptual analysis of the study objective. Results indicate a non-affectation by chemical residues of pesticides in any of the evaluated matrixes; and satisfactory quality of the waters for fishing use according to the used hydrological indicators. Ignorance exists on the farmer part on the application and dose of these chemical products, and recommendations are offered on pesticide use to prevent future impacts on the ecosystems.


INTRODUCTION
In the southern area of the Guacanayabo gulf, it is carried out the commercial capture of Penaeus sp. shrimps, fish and crustaceans as the common lobster of the Caribbean Panulirus argus (Latreille, 1804), and the mangrove oyster (C. rhizophorae).
In Cuba, the capture of these resources has diminished in the last 20 years, due to different natural factors and of human origin, such as the damming of rivers and its consequent reduction in the contribution of nutritious inorganic to the coastal area (Baisre and Arboleya, 2006). Contamination has also been pointed out by heavy metals and chemical pesticides coming from agriculture (Arencibia-Carballo et al., 2014). Due to the fishing environmental and biological importance of the Manzanillo -Niquero coastal region, the irrational use of pesticides constitutes a serious problem, due to the adverse effects th at it causes in the health of the aquatic and marine organisms, as well as in coastal ecosystems and the environment (Arencibia, 2005). Although one knows that in the last years it has happened a decrease in Cuba of the inorganic sources of contamination (Montalvo et al., 2010) and less toxic pesticides to the environment and man are used, as the buprofezin insecticide, used for the control of insectpests in rice and potato (Orta-Arrazcaeta, 2002), it is necessary to diminish risks associated to indiscriminate use of the same ones (Concepción-Villanueva et al., 2016). The study of pesticide residues facilitates the evaluation of the level of contamination (Zhang et al., 2012). The Fishery Research Center (CIP) of Cuba carries out an environmental monitoring in a periodic way, in waters, sediments and organisms of fishing interest, where pesticide determination is a complementary analysis. Being the objective of the present paper the determination of residues of chemical pesticides in water and superficial marine sediment, as well as in shells of mangrove oyster (Crassostrea rhizophorae), of the Manzanillo-Niquero coastal area, in the Guacanayabo gulf.

II. MATERIALS AND METHODS
The study area is located in the southeastern region of Cuba, Granma province, and it covered the coastal area, from 20°21.204'N and 077°08.156'W (Manzanillo city) up to 20°03.276'N, 077°36.266'W (Niquero municipality), it has a total surface of 8 969 km 2 and a current population of 47 475 inhabitants, (Fig. 1).

Fig.1: Sampling network , main populations and hydrographical basins in the study area.
The sampling network included 10 coastal seasons ( Fig. 1) that were sampled in May and June, 2016, months of high temperature and rainfalls, since high temperatures increase the incidence of pests and the use of chemical pesticides can increase, and significant rainfalls induce a bigger terrigenous runoff with a bigger probability of contamination of coastal marine ecosystems . For pesticide residues there were taken sediment samples in all seasons, water samples in four seasons and oyster shells in the region of Campechuela, forming a sample made up of 10 shell kg. Water samples were collected with a Van Dorn bottle at 30 cm depth and stored in wide mouth amber glass bottles while sediment samples were collected with a dredger and they were stored in black nylon bags, being conserved frozen until their transfer to the destination laboratories . Oyster shell samples went to the Research Center for the Mining and Metallurgical Industry (CIPIMM) to be grinded and to homogenize in a ball mill, next, they were sifted to 0.1 mm and they were sent joined to the samples of the different matrixes to the Chemistry laboratory of the National Institute for Vegetable Health Research (INISAV) for the analysis of pesticide residues in a gas chromatograph, M-DANI brand, whose detection limit for quantification is 0.2 µg/L and an uncertainty based on the standard deviation of0.4 (Ricardo-Mariño, 2009). In each season, there were carried out in situ recordings of water temperature (°C), pH, salinity (ups), oxygen saturation (%), concentration of dissolved oxygen (mg L -1 ) and total dissolved solids (mg/L), at 0.50 m depth, with a HANNA HI 9828 multi-parametric probe with an error (precision) of ± 0.1 units. Data averages are shown with their standard deviation (± DS). In parallel it was carried out a survey to 85 farmers that inhabit near towns to the coastal area, to obtain information about the pesticide type used, dose and application frequency by crop types, for conceptual analysis of the outlined study object (I annex 1).

III. RESULTS AND DISCUSSION
The results of hydrological sampling are shown in Table 1. They indicate that the evaluated parameters didn't show indicative values of contamination, with concentrations in salinity (<34.7), of oxygen over 4 mg/L and dissolved solids (<100 mg/L), so it is considered of Good and Fair quality according to NC-25 the Cuban standard for fishing use (1999). The pH showed values characteristic of marine waters, and the average concentration and saturation of oxygen are acceptable, keeping in mind that the region shows a high degradation of organic matter, and bigger oxygen consumption than production of the same one (Montalvo and Perigó, 1999); The results of pesticide residues demonstrate that contamination doesn't exist in the coastal area below 0.2 µg/L, which could be a consequence that in the last years they have been applied rationally, or due to low concentrations, and when being highly biodegradable compounds in the marine ecosystem, added to the high temperatures of the region, they´re not detectable with the techniques being used. Pesticide analyses didn't detect chemical residues in water, sediment, or accumulations in the oyster shells (Table 2), (quotation). The results of the surveys carried out for the same period of study in the population of the coastal area are shown. Only 9 comments a bigger representativeness in the sampling of superficial water requires several samplings at different times and with more frequency, because when there are marine currents, it is constantly flowing and chemical residues are not retained because they´re beingdrawn by the same ones. It also could be sampled the sediment of the intertidal area as the high tide and low tide processes can contribute to their deposition in the coastal coast area. Absence of chemical pesticides in the study area can be used as baseline to evaluate future events that can involve these compounds, which would allow a precise analysis of their persistence, Methods of integrated handling of pests and agrienvironment politics are also developed. This has allowed the significant substitution of imported chemical pesticides, decrease of the toxic load on the ground and underground waters, improvement of the conservation of functional biodiversity, among other. The results of applied surveys don't allow to draw conclusions, but they give a vision of the risk, although it is recognized that the type of question to formulate and the hypothesis of the problem, determine in great measure the research design that we should use (Meltzoff, 2000).

IV. CONCLUSIONS
There were not found residues of chemical pesticides in the different evaluated matrixes, for what it is considered that the evaluated coastal area doesn't present contamination due to pesticides. Hydrological variables showed acceptable quality and in consequence with the period of sampling, of significant rainfalls. An ignorance of the appropriate use of pesticides exists on the part of some (put the %) farmers .

V.
RECOMMENDATIONS Annually maintain a pesticide monitoring in critical points of the Manzanillo-Niquero coastal area. Carry out pesticide analysis not only in the oyster shell but also in samples of the animal meat.