The worldwide use of semi-persistent organophosphate pesticides has become increasingly frequent and notorious. Their presence is registered in both continental and coastal waters; the latter ones are known for their subtly balanced environmental richness, difficult to recover once lost. These xenobiotics compounds reach the coastal zone through rivers that have crossed human settlements, as well as through peripheral run-off water used to exterminate agricultural pests. In Mexico, a developing country, the use of pesticides for several decades has not been adequately regulated, which is why various coastal ecosystems are the accumulation areas of these agrochemicals used in the continent. In the Gulf of Mexico, one of the coastal systems of high fishing importance for many years is the lagoon of Alvarado and receives the discharges of two great rivers, Blanco, Limón and Papaloapan, which travel more than 200 km from its source to the sea, crossing large extensions of farmland where there are also livestock activities and the use of these pesticides. For this reason, the objective of this work was to determine the presence of organophosphate pesticides in the Alvarado lagoon at the Gulf of Mexico as a potential aspect of high impact contamination. Five pesticides have been identified in the lagoon sediments, of which the most important and highest concentrations are Dimethoate and Chlorpyrifos, with 75.65 - 79.0 ng/g and 0.17 - 0.23 ng/g respectively, both internationally classified as moderately toxic. These concentrations were comparable to levels in other world regions with intense agricultural activity and vector control like the Mediterranean Sea and the lagoon of Alvarado was evidenced as a hot spot for the accumulation of these organophosphates with the high risk for the benthic organisms and for the human health when consuming these fishery products.
Organophosphate pesticides (OPs) are the chemical compounds most used in the world, representing between 30% and 40% of insecticide sales in the planet [
The geographic coordinates of the Alvarado lagoon are: 18˚43'51" and 18˚52'40"N - 95˚42'23" and 95˚57'25"W, with an area of 4452.5 ha, and a maximum depth of 2.6 m. It connects with the Gulf of Mexico through a marine mouth and a 0.4 km wide barrier. The great Alvarado Lagoon System (SLA for its initials in Spanish) is constituted by interconnected lagoons as Buen País and Camaronera and large number of interior lagoons like Tlalixcoyan, among others; and the Blanco, Camarón, Acula, Palma Real and Papaloapan rivers (
Samples of surface sediments were collected using a van Veen dredge to obtain the first 5 cm of the sedimentary column in 10 lagoon sites (
Sampling sites of surface sediments | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Organophosphate pesticides (OPs) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | Mean ± SD | Molecular weight | Log Kow | Water solubility (mg/L) |
Chlorpyrifos | 203.8 | 215.0 | 167.8 | 165.4 | 199.6 | 207.4 | 224.0 | 209.4 | 225.5 | 195.7 | 201.4 ± 20.7 | 350.6 | 4.5-5.3 | 0.3 - 1.4 |
Chlorpyrifos methyl | <2.0* | <2.0* | <2.0* | <2.0* | <2.0* | <2.0* | <2.0* | <2.0* | 43.9 | <2.0 | 322.5 | 4.3 | 4.0 | |
Diazinon | <0.4* | <0.4* | <0.4* | <0.4* | <0.4* | <0.4* | <0.4* | <0.4* | <0.4 | <0.4 | 304.3 | 3.8 | <1.0 | |
Dimethoate | <8.3* | <8.3* | <8.3* | <8.3* | <8.3* | <8.3* | <8.3* | <8.3* | 78,999.6 | 78,651.7 | 78,825.7 ± 246.0 | 229.2 | 0.8 | 1 - 10.0 |
Dioxanthion | <1.0* | <1.0* | <1.0* | <1.0* | <1.0* | <1.0* | <1.0* | <1.0* | <1.0* | <1.0* | 456.5 | 3.0 | <0.1 | |
aEPN | <7.4* | <7.4* | <7.4* | <7.4* | <7.4* | <7.4* | <7.4* | <7.4* | <7.4* | <7.4* | 323.3 | 4.8 | Insoluble | |
Ethion | <1.9* | <1.9* | <1.9* | <1.9* | <1.9* | <1.9* | <1.9* | <1.9* | 555.4 | 418.1 | 486.8 ± 97.1 | 384.5 | 5.1 | 2.0 |
Fenchlorphos | 48.9 | 28.0 | 31.0 | 38.9 | <0.3* | <0.3* | 36.8 | <0.3* | <0.3* | <0.3* | 36.7 ± 8.1 | 321.5 | 5.1 | 1.0 |
Malathion | <6.6* | <6.6* | <6.6* | <6.6* | <6.6* | <6.6* | <6.6* | <6.6* | <6.6* | <6.6* | 330.3 | 2.4 | 143.0 | |
Parathion | <2.2* | <2.2* | <2.2* | <2.2* | <2.2* | <2.2* | <2.2* | <2.2* | <2.2* | <2.2* | 291.2 | 3.8 | 11.0 | |
Parathion methyl | <1.8* | <1.8* | <1.8* | <1.8* | <1.8* | <1.8* | <1.8* | <1.8* | <1.8* | <1.8* | 263.2 | 2.9 | 37.7 | |
Terbufos | <0.5* | <0.5* | <0.5* | <0.5* | <0.5* | <0.5* | <0.5* | <0.5* | <0.5* | <0.5* | 288.4 | 4.5 | 5.1 | |
∑OPs | 252.7 | 243.0 | 198.8 | 204.3 | 199.6 | 207.4 | 260.8 | 209.4 | 79,824.4 | 79,265.5 | 16,086.6 ± 33,445.8 | NR | NR | NR |
p, p’-DDT (organochlorine pesticide) | 354.5 | 6.4 - 6.9 | Insoluble |
*Detection limits (LOD) (pg/µL); aEPN (Ethyl p-nitrophenyl benzenethiophosphonate); NR: Not Reported.
concentrations of stations 7, 1, 2, in descending order, were 260.8, 252.7 and 243.0 pg/g respectively, followed by sites 4, 6 and 8 with contents between 204 and 209 pg/g and finally, stations 3 and 5 with levels between 198 and 199 pg/g. Except for the maximum contents of points 9 and 10, the results determined in the rest of the analyzed sediments at the level of total concentration had a comparable magnitude between 198.8 and 260.8 pg/g which would mean that these agrochemicals are used in the surrounding areas of the lagoon, and that the urban and agricultural area of Alvarado is the main pollutant source which explains the high records found.
One of the few phosphorus compounds reliably quantified was Chlorpyrifos, which was determined in all samples and had a concentration range between 165.4 (station 4) and 225.5 (station 9) pg/g; its methylated form was only detected in site 9 with a content bellow (43.9 pg/g). Dimethoate was exclusive of the sediments of the marine interaction zone (stations 9 and 10) with the maximum values already mentioned (>7000 pg/g) same as Ethion, with unique concentrations in these sampling stations, with levels of 555.4 and 418.1 pg/g respectively. The last organophosphate pesticide found in the sedimentary matrix of the Alvarado lagoon was the Fenchlorphos in sites 1 to 4 and 7, with contents ranging from 28.0 (station 2) to 48.9 (station 1) pg/g. It is important to highlight the absence of this compound in the area inside the Tlalixcoyan lagoon (stations 5 and 6), as well as in the region of Port of Alvarado and the lagoon marine mouth (sites 8, 9 and 10) (
Some of the main physicochemical characteristics of the evaluated molecules provide information on their degree of persistence.
As can be seen, Dimethoate has a Log Kow < 1 and can be considered the least persistent of the group of evaluated organophosphates. Malathion and Parathion-methyl with Log Kow < 3 would follow, contrasting with the environmental behavior of Chlorpyrifos, Ethion, EPN and Fenchlorphos, since their octanol-water partition coefficient is between 4.8 and 5.27 as well as their aqueous solubility, with values from insoluble to 2 mg/L, and it is these molecular characteristics that could favor their permanence for longer periods of time in the environmental matrixes, resulting high degree of persistence at the sediment with harmful effects on the benthic community.
In Mexico there is no established regulation that mentions the highest allowed limits of pollutants in coastal and marine sediments. In the case of pesticides, the
2016 Official Pesticide Catalog, issued by the Federal Commission for the Protection against Sanitary Risks (COFEPRIS for its initials in Spanish), an entity subordinated to the Ministry of Health, should be considered [
Terbufos is category 1 since its median lethal dose (LD50), ingested orally by rats as test animals, is 1.3 mg/kg, and dermally, by rabbits, is 0.87 mg/kg, it is therefore classified as extremely hazardous, belonging to the class Ia according to the World Health Organization classification [
Pesticides | Uses | LD50 (mg/kg) | Acute toxicologic category | Effects on the environment | Ground water (µg/L) | Surface waters (µg/L) | Marine sediments (ng/g) | Soils (ng/g) | |||
---|---|---|---|---|---|---|---|---|---|---|---|
Fresh | Marine | ||||||||||
Acute | Chronic | Acute | Chronic | ||||||||
Chlorpyrifos (ethyl and methyl) | Agricultural, domestic, cattle-ranching, urban, industrial | 96 (Rats/oral) >2000 (rats/ dermal) | 3 | Very toxic to fish, birds and bees | 30.0 | 0.083a | 0.041a | 0.011a | 0.0056a | NR | NR |
Diazinon | Agricultural, domestic, cattle-ranching, urban, industrial, gardening | 1250 (Rats/oral) > 2020 (rabbit/ dermal) | 4 | Highly toxic to birds, fish and bees | 20.0 | 0.17 | 0.17 | 0.82 | 0.82 | 1.9 | NR |
Dimethoate | Agricultural, gardening, industrial | 235 (Rats/oral) >400 (rats/ dermal) | 3 | Moderate to high Toxicity to aquatic organisms and birds. Extremely toxic to bees | 6.0 | NR | 6.2CA 0.15NZ | NR | NR | NR | 218.0M |
Dioxathion | Agricultural, cattle-ranching, domestic, gardening, urban, industrial | 23 - 64 (Rats/oral) | 2 | Very toxic to aquatic organisms | NR | NR | NR | NR | NR | NR | NR |
EPN | Agricultural, cattle-ranching, domestic, gardening, urban, industrial | 17.8 (Rats/oral) 30 (rabbit/ dermal) | 2 | Very toxic to aquatic organisms | NR | NR | NR | NR | NR | NR | NR |
Ethion | Agricultural, cattle-ranching | 21 (Rats/oral) 838 (rabbit/ dermal) | 2 | Highly toxic to fish and birds. Not toxic to bees | NR | NR | NR | NR | NR | NR | NR |
Fenchlorphos | Agricultural, gardening | 1250 (Rats/oral) 1000 - 2000 (rabbits/ dermal) | 4 | Very toxic to aquatic organisms | NR | NR | NR | NR | NR | NR | NR |
Malathion | Agricultural, cattle-ranching, gardening, urban, industrial | 5500 (Rats/oral) > 2000 (rabbits/ dermal) | 4 - 5 | Slightly to extremely toxic to fish. Moderately toxic to birds, highly toxic to bees | 190.0 | NR | 0.1 | NR | 0.1 | 0.67 | NR |
Parathion (parathion methyl) | Agricultural, industrial | 6 (Rats/oral) 66 (rat/dermal) | 2 | Toxic to aquatic and terrestrial organisms | 50.0b | NR | 0.065b | 0.013b | NR | NR | 0.34V |
Terbufos | Agricultural | 1.3 (Rats/oral) 0.87 (rabbits/ dermal) | 1 | Extremely toxic to birds, mammals, reptiles, fish and other aquatic organisms | NR | NR | NR | NR | NR | NR | NR |
aonly for Chlorpyrifos; bonly for Parathion; NR: Not Reported; CA: Canadian Water Quality Guidelines; NZ: quality criteria for epicontinental waters in Australia and New Zealand; M: Toxicity towards mammals; V: Toxicity towards plants.
document for this group of pesticides are the same, from the agricultural to the industrial, including domestic and gardening uses. Likewise, the qualitative description of its toxicity indicates a gradient going from slightly toxic for fish (Malathion), to extremely toxic for bees, birds, fish and mammals (Dimethoate and Terbufos) [
Regarding the compounds detected in this study, for Chlorpyrifos in its ethyl and methyl forms, the Mexican Catalog reports oral and dermal LD50 of 96 and >2000 mg/kg and classifies it as acute toxicological category 3, while WHO includes it in the group of moderately hazardous (class II), being very toxic for bees, birds and fish. Dimethoate has a lower number of established uses, being and authorized for agricultural, industrial and landscaping purposes, not for domestic and livestock related uses, with a toxicity classification of 3, moderately hazardous like Chlorpyrifos, with different LD50, 235 and >400 mg/kg for oral and dermal intake in rats, respectively.
The Pesticide Official Catalog of Mexico establishes two uses for Ethion, agricultural and livestock-related, belonging to group 2 due to its acute toxicity, with LD50 of 21 and 838 mg/kg in tests, oral in rats and dermal in rabbits, and highly toxic for fish and birds, but not for bees. Fenclorfos has few registered uses, mainly in agriculture and gardening, with median lethal dose of 1250 mg/kg orally in rats, and 1000 - 2000 mg/kg dermally in rabbits; it belongs to highly toxic category 4, very toxic to aquatic organisms (
Even though we did not quantify levels above the limits of detection in most of the organophosphate pesticides in the lagoon, it is important to mention the discrepancies regarding the acute toxicity and the danger of classifying these compounds considering what has been established in a standardize [
Another fundamental aspect affecting the presence, accumulation and effects of these and other pesticides in Mexican ecosystems―including coastal ones such as the Alvarado lagoon―is the number of commercial entities with official records from the COFEPRIS for their distribution and use. In Annex 2 of the 2016 Official Pesticide Catalog there are, for Chlorpyrifos only its ethyl and methyl forms, 171 records out of a total of 5524 (3.1%), most of indeterminate validity, which allows their continuous use. Dimethoate has 79 records (1.4%) all of them with no expiration date. For Ethion there are only eight registers (0.14%) and, just as in the previous cases, with indeterminate validity. Officially, these three pesticides have an insecticide-acaricide use. It is worth mentioning that Fenchlorphos, found in this study, is not registered with COFEPRIS, which means it is not authorized in Mexico [
Thanks to scientific efforts of the highest quality, mainly from developed countries both in America and Europe, there are today environmental quality criteria for diverse ecosystem matrixes whose purpose is to provide reference of contaminant concentrations which can damage water, sediments and soil. The National Oceanic and Atmospheric Administration of the American Department of Commerce in the USA (NOAA), has gathered all this information and created the well-known Screening Quick Reference Tables or SQuiRTs [
For most of the organophosphate pesticides found in this study there is no ecotoxicological reference data from NOAA for marine sediments; however, we consider that it is important to present guide concentrations of possible effects established for groundwater, continental and marine surface water, soils and the average lethal dose (acute and chronic toxicity) that this environmental agency has available from some OPs analyzed in this work. These criterion concentrations are presented in
In studies of this nature, with not much background information on records of these pesticides, we need to compare our results with others from similar coastal environments with similar problems caused by the intensive use of these agrochemicals.
Within the specific framework of individual organophosphate compounds, Chlorpyrifos is the pesticide with more data to compare; concentrations found in this study were similar to the lowest reported ranges in sediments of the Zigo River in Togo, Africa [
Area | ∑OPs | Chlorpyrifos | Dimethoate | Diazinon | Malathion | Reference |
---|---|---|---|---|---|---|
Africa | ||||||
Zigo River, Togo | 0.82 - 26.93 | ND | ND | ND | [ | |
Asia | ||||||
Guan River, China | 0.0 - 2.18 | [ | ||||
America | ||||||
Zumpango Lake, Mexico | 5120.0 | 110.0 | [ | |||
Europa | ||||||
Portuguese rivers | 11.5 - 19.2 | [ | ||||
Arc River, France | 0.01 - 0.02 | [ | ||||
Guadalquivir River, Spain | 0.7 - 15.9 | 0.2 - 175.5 | [ | |||
Mediterranean Sea | ||||||
Damietta Channel, Egypt | 303.8 | 279.0 | 5.12 | [ | ||
Llobregat & Anoia rivers, Spain | ND | 0.09 - 1.29 | ND | [ | ||
Llobregat River, Spain | 0.39 - 130.97 | 0.04 - 2.53 | [ | |||
Berre Lagoon, France | ND | [ | ||||
Turia & Jucar rivers, Spain | 4.51 - 55.95 | ND | ND | ND | [ | |
Tiber River, Italy | 1.42 - 68.5 | 0.26 - 32.85 | ND | 0.18 - 0.54 | ND | [ |
Alvarado Lagoon, Mexico | 0.2 - 79.8 | 0.17 - 0.23 | 78.7 - 79.0 | ND | ND | This study |
ND: Not Detected (
Lake, Estado de Mexico, with 110 ng/g [
The insecticide Dimethoate inhibits the acetylcholinesterase enzyme which causes the accumulation of the neurotransmitter acetylcholine and increases the cholinergic synapse. The effect of this organophosphate is similar in insects and mammals, the main difference being the way it is eliminated, as mammals are more efficient eliminating it through urine (87% - 90%) [
Organophosphate pesticides are found in the complex assembly of agrochemicals in coastal sediments; here, organochlorines and pollutants of industrial origin like the polychlorinated biphenyls, can cause a combined exposure from the intrinsic sedimentary toxicity involving unknown or poorly documented interactions causing high impact damage [
This information is a first approach to the presence of OPs in sediments of the Alvarado lagoon; there are many studies from this coastal area of the Gulf of Mexico regarding biological, geological, fishing, hydrodynamic, socioeconomic and, to a lesser extent, environmental factors, that focus mainly on metals, sanitary microbiology, organochlorine pesticides, water quality, change in geochemical signals of sedimentary accumulation due to important historical modifications in the basin, among others [
Five organophosphate pesticides were recorded in the sediments of the Alvarado lagoon. Chlorpyrifos was recorded in all analyzed sites, with low concentrations when compared to reports from several coastal environments around the world. Fenchlorphos was recorded in half of the analyzed samples, mainly in the central-northern region of the study area. Ethion and Dimethoate were registered in the influence area in the Port of Alvarado in connection with the Gulf of Mexico. Our study found that Dimethoate was the organophosphate compound with the highest concentration, with levels like those reported for polluted rivers that discharged into the Mediterranean Sea and this represented a high risk for benthos. Therefore, it can be classified to the Laguna de Alvarado, in particular to the area under the influence of the Port of Alvarado, as a hot spot site by organophosphate pesticides. The presence of these compounds in sediments constitutes scientific evidence of the impact of human settlements and their activities such as agriculture and livestock around the study area reaches it mainly through river runoff. These pesticides are used to control vectors, such as insect pests in order to avoid health problems from tropical diseases such as malaria and dengue fever, despite the risk of chemical contamination to the benthic organisms and long-term ecological disturbances on this biological community of great relevance to coastal ecosystems. Without enough studies of this type, there is not enough reliable data to define more effective control policies, with less environmental and human health consequences.
The authors wish to thank Salvador Hernández Pulido, academic technician, for elaborate the figures 1 and 2 that correspond to the study area with sampling sites, and distribution concentration of organophosphate pesticides at Alvarado lagoon, respectively and by correctly ordering the references in the text and in the corresponding section.
Funding was provided by Instituto de Biología, Universidad Nacional Autónoma de México, México Project 602 Alvarado Lagoon.
The authors declare no conflicts of interest regarding the publication of this paper.
Ponce-Vélez, G. and de la Lanza-Espino, G. (2019) Organophosphate Pesticides in Coastal Lagoon of the Gulf of Mexico. Journal of Environmental Protection, 10, 103-117. https://doi.org/10.4236/jep.2019.102007