Introduction
⌅In a context in which industrial environmental pollution is a source of conflict, there is a need to promote social responsibility committed to the preservation, restoration and care of the environment as a central strategy to promote the health of the inhabitants of the affected areas (Guzmán et al., 2019GUZMÁN, M.A.R.; CRUZ, P.O.; VALDÉS, C.R.: “Efectos de la contaminación por metales pesados en un suelo con uso agrícola”, Revista Ciencias Técnicas Agropecuarias, 28(1), 2019, ISSN: 2071-0054.). This problem is undoubtedly one of the most important ones affecting 21st century society according to CEPAL (2021)CEPAL: Cuarto informe sobre el progreso y los desafíos regionales de la Agenda 2030 para el Desarrollo Sostenible en América Latina y el Caribe., [en línea], Ed. CEPAL, Santiago de Chile, Chile, 2021, Disponible en:https://foroalc2030.Cepal.org/2021/es/..
This environmental situation could compromise the fulfillment of some of the millennium goals and affect the process of updating the economic and social model in Cuba, which would guarantee a more just, equitable and inclusive society, moving along the path of sustainable development, which integrates its three dimensions: economic, social and environmental (NN.UU., 2021NN.UU.: Agenda 2030 Informe nacional Voluntario, CUBA 2021124 p, Inst. NN.UU., La Habana, Cuba, 124 p., 2021.).
This is influenced by the development of certain industrial activities that constitute a moderate risk of environmental pollution, given the leaks of components that accumulate in the soil from the natural channel and irrigation with wastewater and as a consequence, "contaminated soil" may appear (Valdés et al., 2017VALDÉS, C.R.; CRUZ, P.O.; BALBÍN, A.M.I.; GURIDI, I.F.; GUZMÁN, M.A.R.; MESA, P.M.A.; MILANÉS, A.F.; KAEMMERER, M.; SÁNCHEZ, J.M.: “Fitogestión (FITOG-MP): tecnología para recuperar áreas contaminadas con metales pesados”, Revista Ciencia Universitaria, 15(1), 2017.). One of the most persistent pollutants are heavy metals (HM), although their negative effects on animal and human health are manifested in the long term (Alarcón et al., 2015ALARCÓN, S.; GRANA, S.; VALDÉS, C.; GOICOCHEA, B.: “Contaminación con metales pesados alrededor de la Empresa de Cerámica Blanca “Adalberto Vidal”, San José de las Lajas. Percepción del riesgo”, Revista de Gestión del Conocimiento y el Desarrollo Local, 2(1): 62-67, 2015, ISSN: 2707-8973.; Doležalová et al., 2019DOLEŽALOVÁ, W.H.; MIHOČOVÁ, S.; CHOVANEC, P.; PAVLOVSKÝ, J.: “Potential ecological risk and human health risk assessment of heavy metal pollution in industrial affected soils by coal mining and metallurgy in Ostrava, Czech Republic”, International journal of environmental research and public health, 16(22): 44-95, 2019, ISSN: 1660-4601.).
To solve these problems that arise, there are treatment techniques based on the ability of different organisms (plants and microorganisms) to degrade, extract or immobilize pollutants from water or soil. These techniques have been called Bioremediation and, as a particular case when using different plants, Phytoremediation (Becerril et al., 2002BECERRIL, J.; BARRUTIA, O.; HERNANDEZ, A.; PLAZAOLA, J.; HERNÁNDEZ, A.; GARBISU, C.: Fitorremediacion y biorremediacion: nuevas tecnologias biologicas para la eliminacion de los contaminantes del suelo., Ed. CCMA-CSIC, Ciencia y Medio Ambiente, II Jornadas Científicas ed., 145-152 p., 2002, ISBN: 84-699-7972-8.; Ardizzi, 2018ARDIZZI, M.: La biorremediación aplicada a la rehabilitación de suelos contaminados con hidrocarburos, Editores: Lucrecia Brutti-Marcelo Beltrán-Inés García de Salamone ed., 137 p., 2018.).
Plants used for such purposes accumulate in their aerial tissues both essential elements for crops (Fe, Mn, Zn, Cu, Mg, Mo, Ni) and non-essential elements or elements with biological functions yet to be determined (Cd, Cr, Pb, Ag, Se, Hg), reaching very high concentrations that are toxic to most plants Gonzales et al. (2017)GONZALES, J.; ACEBEDO, J.; ARMAS, C.; CUSTODIO, M.; GARCÍA, M.; GONZALES, A.; VÁSQUEZ, M.: “Fitorremediación de un suelo con exceso de cobre utilizando cuatro especies vegetales;“girasol”,“alfalfa”,“geranio” e “higuerilla”, Searching-science, 1(1): 1-12, 2017.; Alonso et al. (2018)ALONSO, B.J.N.; MONTAÑO, A.N.M.; SANTOYO, P.G.; MÁRQUEZ, B.L.; SAUCEDO, M.B.C.; SÁNCHEZ, Y.J.M.: “Biorecuperación y fitorremediación de suelo impactado por aceite residual automotriz”, Journal of the Selva Andina Research Society, 9(1): 45-51, 2018, ISSN: 2072-9294.; Lama (2018)LAMA, E.: “Fitoextracción de plomo en suelos de tres parques por el girasol (Helianthus annuus) inoculado con el hongo micorrítico Glomus intraradices”, 2018, Disponible en:http://repositorio.lamolina.edu.pe/handle/UNALM/3499 , so those used for such purposes should not be consumed by animals or humans.
In this case, nickel and copper are essential elements for plants that, in high concentrations, cause disorders in the human body such as heart damage and skin irritation, damage to the nervous system, liver and kidney function, the musculoskeletal system, etc., specifically in the child population that is more sensitive to these effects. This situation is exacerbated because the concern for having guaranteed food led man to cultivate and propagate plant species in agricultural areas close to industrialized or contaminated areas, which according to Valdés et al. (2017)VALDÉS, C.R.; CRUZ, P.O.; BALBÍN, A.M.I.; GURIDI, I.F.; GUZMÁN, M.A.R.; MESA, P.M.A.; MILANÉS, A.F.; KAEMMERER, M.; SÁNCHEZ, J.M.: “Fitogestión (FITOG-MP): tecnología para recuperar áreas contaminadas con metales pesados”, Revista Ciencia Universitaria, 15(1), 2017., is a global reality, and Cuba is no exception.
By taking on the challenge, the Faculty of Agronomy-UNAH studies the problems of heavy metal contamination in vulnerable agroecosystems (Guzmán et al., 2021GUZMÁN, M.A.R.; VÁZQUEZ, P.O.; CRUZ, O.; VALDÉS, R.; VALDÉS, P.: “Fitotecnología para la recuperación de agroecosistemas contaminados con metales pesados por desechos industriales”, Centro Agrícola, 48(2): 5-11, 2021, ISSN: 0253-5785 ISSN on line: 2072-2001.).
Despite the existence of the National Environmental Strategy (EAN) 2021-2030 CITMA-Cuba (2021)CITMA-CUBA: Estrategia Ambiental Nacional (EAN) 2021-2030, Etapa 2021-2025, Inst. Ministerio de Ciencia, Tecnología y Medio Ambiente, La Habana, Cuba, 25 p., Publisher: MINISTERIO DE CIENCIA, TECNOLOGÍA Y MEDIO AMBIENTE, 2021., in Cuba, there are areas in the country where, for various reasons, the necessary environmental safety is not met, such as the case of the municipality of San José de la Lajas, in Mayabeque, where 78% belongs to the industrial sector, and although it constitutes an important line in the economy, it is considered a source of environmental pollution and an impact on local food security (ONEI-Cuba, 2019ONEI-CUBA: Anuario Estadístico de Cuba 2018. Oficina Municipal de estadística e información en Mayabeque, 2012-2018, [en línea], Inst. Oficina Nacional de Estadísticas e Información, Anuario Estadístico de Mayabeque, Anuario estadístico, San Jose de las Lajas Mayabeque, CUBA, 2019, Disponible en:http://www.one.cu/aed2018/.).
Taking into account the situation presented, the work aims to propose mathematical models to predict the behavior of nickel and copper concentrations in an agroecosystem, adjacent to the dumping of industrial waste in the municipality of San José de las Lajas.
Materials and methods
⌅The experimental site corresponds to an agricultural area, located 200 m from the source of contamination (Company Cerámica Sanving S.A.) at 22º57’49.66’’ N, 82º10’13.02’’ W and 22º58’7.95’’ N, 82º10’13.60’’ W, according to the Cuba Norte coordinate system, and adjacent to the waste dump. The site belongs to farmers who participate in the Urban, Suburban and Family Agriculture Program of the Jamaica People’s Council, San José de las Lajas municipality, Mayabeque, on a soil classified as Ferralitic Yellowish Leached, according to Hernández et al. (2015)HERNÁNDEZ, J.; PÉREZ, J.; BOSCH, I.; CASTRO, S.: “Clasificación de los suelos de Cuba 2015”, Mayabeque, Cuba: Ediciones INCA, 93: 91, 2015.. The crop plots produce vegetables and grasses of the Cynodon genus belonging to the Poaceae family, for free animal consumption, which according to Guzmán et al. (2021)GUZMÁN, M.A.R.; VÁZQUEZ, P.O.; CRUZ, O.; VALDÉS, R.; VALDÉS, P.: “Fitotecnología para la recuperación de agroecosistemas contaminados con metales pesados por desechos industriales”, Centro Agrícola, 48(2): 5-11, 2021, ISSN: 0253-5785 ISSN on line: 2072-2001. accumulate high concentrations of these heavy metals in their leaves.
Study of heavy metal content in soil
⌅“The data series corresponding to the values of 42 samples of concentration of heavy metals Nickel and Copper was taken from 2005 to 2018, provided by the FITOPLANT Scientific Group of the Faculty of Agronomy of UNAH”. The values were compared with the maximum permissible limits and dangerous levels for soil and plants, proposed by Kabata (2010)KABATA, P.: Trace elements in soils and plants, Ed. CRC press, DOI: http://dx.doi.org/10.1201/b10158 p., 2010, ISBN: 0-429-19112-X. & Fadigas et al. (2006)FADIGAS, F. de S.; SOBRINHO, N.M. do A.; MAZUR, N.; CUNHA DOS ANJOS, L.H.: “Estimation of reference values for cadmium, cobalt, chromium, copper, nickel, lead, and zinc in Brazilian soils”, Communications in soil science and plant analysis, 37(7-8): 945-959, 2006, ISSN: 0010-3624..
Mathematical analysis to estimate decontamination in the study area of copper and nickel
⌅Taking into account the concentration of the major elements found in the soil analyses (copper and nickel) according to Guzmán et al. (2021)GUZMÁN, M.A.R.; VÁZQUEZ, P.O.; CRUZ, O.; VALDÉS, R.; VALDÉS, P.: “Fitotecnología para la recuperación de agroecosistemas contaminados con metales pesados por desechos industriales”, Centro Agrícola, 48(2): 5-11, 2021, ISSN: 0253-5785 ISSN on line: 2072-2001., the analyzed of the time in which this soil could be decontaminated was carried out.
To characterize the behavior of the concentrations and analysis of the possible decontamination, the data were tabulated in the Microsoft Excel 2003 program. Next, the simple linear regression was performed with the STATGRAPHICS Centurium XVIII program. The estimation was carried out by the interpolation method with the linear equation Y = a+bx Del Valle et al. (2022)DEL VALLE, M.J.; GONZÁLEZ, V.D.; RAFAEL, P.L.; SÁNCHEZ, A.O.R.; DELGADO, T.C.: “Efecto de las variables climáticas sobre el rendimiento agrícola del arroz (Oryza sativa L.)”, Ingeniería Agrícola, 12(1), 2022, ISSN: 2306-1545, e-ISSN-2227-8761. where “Y” corresponded to the concentration of each variable and “X” years analyzed. In parallel, the behavior and trend for each case were analyzed. In addition, the annual concentration means were analyzed with respect to the Reference Values and Upper Permissible Limit (Fadigas et al., 2006FADIGAS, F. de S.; SOBRINHO, N.M. do A.; MAZUR, N.; CUNHA DOS ANJOS, L.H.: “Estimation of reference values for cadmium, cobalt, chromium, copper, nickel, lead, and zinc in Brazilian soils”, Communications in soil science and plant analysis, 37(7-8): 945-959, 2006, ISSN: 0010-3624.; Kabata, 2010KABATA, P.: Trace elements in soils and plants, Ed. CRC press, DOI: http://dx.doi.org/10.1201/b10158 p., 2010, ISBN: 0-429-19112-X.).
The statistical processing for the prediction of pollution consisted of calculating the confidence intervals of the means by treatments of the variables evaluated, for a confidence level of 99%. The calculated and predicted values were taken into account to prepare the prediction graphs, combining the statistical program STATGRAPHICS Plus for Windows 5.1 and the Excel program, taking into account the equations obtained from the models, predicting until the year 2034.
Results and discussion
⌅It was found that the concentrations of MP in the contaminated soil samples are higher than those determined in the standard soil, which is presented in Table 1.
The following decreasing order in contamination contributions is Ni ˃ Cu, with values of 233 and 57 units of differences respectively between the contaminated soil and the standard soil, which is equivalent to a percentage of 310.66% for Ni above the upper permissible limit, being the one that makes the greatest contribution to the soil, which means that when exceeding the intervention limit of said standards, it is classified as a soil in need of urgent remediation due to these concentrations.
| Samples | Ni ± std | Cu ± std |
|---|---|---|
| mg kg-1 | ||
| Standard | 84± 29 | 364± 98 |
| Contaminated | 317± 25 | 421± 32 |
| VRa | 35 | 36 |
| VIa | 210 | 190 |
| LSPb | 75 | 100 |
| CTc | 74 | 55 |
a- Reference Values (VR) and Intervention Values (VI) of the Dutch Standards.
b- Upper Permissible Limit in soils.
c- Values reported for the Earth's crust.
Figure 1 shows a comparison of the intervention limits with respect to the concentration percentages of the metals Ni and Cu to mitigate the excessive increase in these soils, since despite being essential elements for plant growth, when they exceed the standard values they become food toxins with the consequent risk to animal and human health, which is determined by this intervention limit as proposed by Doležalová et al. (2019)DOLEŽALOVÁ, W.H.; MIHOČOVÁ, S.; CHOVANEC, P.; PAVLOVSKÝ, J.: “Potential ecological risk and human health risk assessment of heavy metal pollution in industrial affected soils by coal mining and metallurgy in Ostrava, Czech Republic”, International journal of environmental research and public health, 16(22): 44-95, 2019, ISSN: 1660-4601..
Figure 2 shows the metals compared to the permissible levels for healthy foods (N.P.A.S), average phytotoxic levels (N.M.F) and levels in Cuban agricultural soils (N.S.A, Cuba) (Muñiz, 2008MUÑIZ, U.: Los microelementos en la agricultura [en línea]. edit. Agencia de Información y Comunicacion para la Agricultura (Agrinfor), 2008, 132 p, Ed. Editorial Agroinfor, La Habana, Cuba, publisher: Ministerio de la Agricultura. Instituto de Suelos. La Habana. Cuba., 2008, ISBN: 978-959-246-201-4.).
It can be seen that these elements are found in concentrations much higher than those required by these established levels, obtaining statistically significant differences with respect to the three values with which they are compared. The samples with the highest levels with respect to their indicators are those of Cu, which exceed these limits by very high percentages (1 830%, 421% and 1 472%, permissible levels for healthy foods, average phytotoxic levels and levels in Cuban agricultural soils, respectively).
All these results have a chemical-biological influence on the crops produced in these areas since, as can be seen, the values with which they are compared are related to food safety Muñiz et al. (2015)MUÑIZ, U.; RODRÍGUEZ, A.; MONTERO, A.; ESTÉVEZ, A.; DE AGUIAR, A.; ARAUJO, D.W.: “El níquel en suelos y plantas de Cuba”, Cultivos Tropicales, 36: 25-33, 2015, ISSN: 0258-5936.; GOC-Cuba (2020)GOC-CUBA: “Decreto Ley 9/2020 “Inocuidad de los Alimentaria””, Gaceta Oficial de la República de Cuba, 76, GOC-2020-675-076, 2020, ISSN: 0864 -0793, e-ISSN: 1682-7511. a property that is of interest in local food safety, in addition to confirming the importance of these studies because under normal conditions these elements are essential for the growth and development of plants.
Analysis of statistical-mathematical models for the description of decontamination in the study area
⌅Figures 3 and 4 for copper and 5 and 6 for nickel present the mathematical statistical models for predicting the minimum time required for the recovery of contaminated soil or the possible reduction of PM concentrations under the study conditions presented. To do so, the company must regulate its discharges of waste to the exterior, taking the necessary measures to meet this objective.
The elements studied show a differentiated behavior, according to the predictions made.
In the case of Cu, according to the logarithmic model and the adjusted models (Figure 4), it shows that its concentrations will probably not begin to decrease until 2035, so the company must review its production process according to UNAH-Cuba (2017)UNAH-CUBA: Técnicas recuperativas para la protección de áreas contaminadas y su impacto en el desarrollo sostenible, Inst. Empresa Cerámica Blanca “Adalberto Vidal”-Grupo FITOPLANT, Grupo FITOPLANT, Agronomía, UNAH., Informe técnico, San José de las Lajas, Mayabeque, Cuba, publisher: Grupo FITOPLANT, Agronomía …, 2017., and the possibilities of recycling or using raw materials with less of this element, coinciding with what was proposed by Alarcón et al. (2015)ALARCÓN, S.; GRANA, S.; VALDÉS, C.; GOICOCHEA, B.: “Contaminación con metales pesados alrededor de la Empresa de Cerámica Blanca “Adalberto Vidal”, San José de las Lajas. Percepción del riesgo”, Revista de Gestión del Conocimiento y el Desarrollo Local, 2(1): 62-67, 2015, ISSN: 2707-8973. & González et al. (2017)GONZÁLEZ, O.L.; DÍAZ, F.J.; CALA, R.D.; BERAZAÍN, R.: “Métodos de inventario de plantas”, En: Diversidad biológica de Cuba: métodos de inventario, monitoreo y colecciones biológicas, pp. 60-85, 2017., who report that the pollutant load can be reduced if its presence in the raw materials used in the production process is reduced.
In the case of Nickel (Figures 5 and 6), the best-fitting model is the exponential one, and it can be seen that since 2019 the levels of this substance have begun to decrease, reaching 0 by 2035, which shows the possibility offered by the regulations complied with regarding the use of raw materials imported from other places in the country such as Moa, which in their nature provide large volumes of nickel, as reported in the UNAH-Cuba (2017)UNAH-CUBA: Técnicas recuperativas para la protección de áreas contaminadas y su impacto en el desarrollo sostenible, Inst. Empresa Cerámica Blanca “Adalberto Vidal”-Grupo FITOPLANT, Grupo FITOPLANT, Agronomía, UNAH., Informe técnico, San José de las Lajas, Mayabeque, Cuba, publisher: Grupo FITOPLANT, Agronomía …, 2017..
For all the above, it must be taken into account that, according to Alloway (2013)ALLOWAY, B.J.: Heavy metals in soils: trace metals and metalloids in soils and their bioavailability, Ed. Springer Netherlands, Alloway B. J. ed., Netherlands, 613, DOI: http://dx.doi.org/10.1007/978-94-007-4470-7. p., 2012, ISBN: 978-94-007-4469-1., one of the most serious problems presented by PM contamination is the half-life of the same, which in the case of copper (Cu) is 740 to 5 900 years, so the effects due to accumulation are more drastic than those produced by contamination caused at a specific time.
Conclusions
⌅The inclusion of mathematical models in contamination studies allowed us to evaluate agricultural areas contaminated with heavy metals and to define that the soils are unusable for agricultural production for consumption, both animal and human, and are classified as requiring urgent remediation due to the concentrations of Ni and Cu.
The mathematical statistical models allowed us to predict that the heavy metals studied have a different behavior; for Ni, their contents have decreased since 2019, but not for Cu, although the areas should not be used for agricultural purposes (at least to grow vegetables or allow free grazing) in the next 10 years.