V-Lacour-Haiti-1

ECOLOGICAL RISK ASSESSMENT OF NITROGEN AND PHOSPHOROUS SUBSTANCES IN URBAN EFFLUENTS OF PORT-AU-PRINCE (HAITI)

Lacour J. (1) Joaneson Lacour is an Agronomist Engineer and currently in the Master of Sciences in Ecotoxicology, Environment and Water Management at Université Quisqueya in Haiti, and working on the Integrated Management of Water Resources under the direction of Evens Emmanuel. Emmanuel, E. (1*)

Professor Evens Emmanuel is actually the Dean of the Faculty of Sciences and Engineering, and the Director of the Laboratory of Water and Environment Quality (LAQUE) of Université Quisqueya in Haiti. He is also the responsible of the Graduate School of Ecotoxicology, Environment and Management of Water. Dr. Emmanuel is teaching Water and Wastewater Treatment. Balthazard-Accou K. (1)

Ketty Balthazard-Accou is a chemist and she received the Master of Sciences in Ecotoxicology, Environment and Water Management of Université Quisqueya in Haiti. She is in charge of the laboratory of chemistry of the Université Quisqueya in Haiti.

Plancher M. J. (1) Michel Plancher Junior is an Environmental Engineer, and currently in the Master of Sciences in Ecotoxicology, Environment and Water Management at Université Quisqueya in Haiti. He is working on the use of active carbon in water and waste water treatment, under the direction of Sara Gaspard and Evens Emmanuel. Marseille J. A. (1) Jean Antoine Marseille an Environmental Engineer, and currently in the Master of Sciences in Ecotoxicology, Environment and Water Management at Université Quisqueya in Haiti. He is working on the use of agricultural by-products, such as sugar cane bagasse, in water and waste water treatment, under the direction of Osnick Joseph and Evens Emmanuel. (1): Laboratoire de Qualité de l’Eau et de l’Environnement, Université Quisqueya, angle rue Chareron et Blvd H. Truman/ BP 796, Port-au-Prince, HT 6120, Haïti, (+509) 466-8400-(+509) 221-4211- evemm1@yahoo.fr

ABSTRACT

The release of nitrogen and phosphorus substances in liquid effluents, contributes to anthropogenic eutrophication of the ecosystem of Port-au-Prince Bay. Information reported in the literature on this ecosystem health conditions put in evidence a significant disappearance of the corals, sedimentation of the natural habitats and proliferation of brown algae. Indeed, the nitrogen and phosphorus play a major part in eutrophication. Certain forms of these nutritive substances are toxic even with relatively weak concentrations. A content of 0,5 NH4 mg/L is toxic for the aquatic organisms. The aim of this study was to allow an ecological risk assessment of nitrogen (nitrates, ammonia) and phosphorus pollutants in liquid effluents generated by Port-au-Prince urban activities. NO3, NH4, PO4 and COD (non-conventional pollutant) have been selected as stressors. Their effects were studied on algae, crustacean, and fish. An approach based on single action of the considered pollutants has been applied to characterize their effects on the selected

organisms by using toxicological information available in the international data bases. 42 samples were collected on the effluents originating from the biggest collector of the city sewer network. Highest concentrations of 22.88 mgNO3/L, of 16 mgNH4/L, of 62 mgPO4/L and of 630 mg COD/L were measured. These concentrations were greater than the threshold values proposed by European commission regulations on effluents discharge in aquatic ecosystem. The scenario allows to a semi-quantitative risk characterization. These first results make it possible to advance that disruptions appear in nutrients cycles, involving a biologic unbalance. Now it will be necessary to verify these first observations on effluents from other points of the sewer network. It will be also interesting to pursue works in order to assess the exposure of aquatic organisms and to understand the effluents dilution process within the bay.

Keywords: Urban effluents, risk assessment, nitrogen and phosphorus substances, dystrophysation, Port-au-Prince bay.

INTRODUCTION

The aquatic ecosystems are generally used in many countries as natural receptacle for the liquid effluents generated by the urban plants, generating a negative interaction between human activities and these environments (Vitousek and Al, 1997; Valiela and Al, 2001). This kind of management of wastewater causes disturbances in nutrients cycles, changes in the structure and the functioning of the biotic community, and a biological unbalance in the aquatic ecosystems (Karr, 1991). The wastewater collected in the urban area of Port-au-Prince, transported in channels of drainage in the open air, is released directly into the sea without any preliminary treatment (Emmanuel and Azaël, 1998). The information reported in the literature on the health of the ecosystem of Port-au-Prince bay makes state of a significant disappearance of the corals, sedimentation of the natural habitats and proliferation of brown algas (Vermande and Raccurt, 2001).

The biological degradation of the high organic matter levels contained in the liquid rejections causes an significant oxygen demand. These processes of natural purification have as a direct consequence the dissolved oxygen uptake of the natural environment and the production of ammoniacal nitrogen starting from the decomposition of the nitrogen organic compounds (Dyer and Al, 1997). In the presence of phosphated compounds the nitrogen substances can cause the eutrophication of the receiving environment, phenomenon in which nitrogen and phosphorus play a major part.

Some nitrogen and phosphate substances are toxic even at relatively weak concentrations. For example, ammonia is toxic around 0.5 mg/L for higher aquatic organisms such as fish (Zimmo and Al, 2004). In addition, phosphorus content higher than 0.5 mg/L constitutes an index of pollution (Rodier, 1996). It should be noted that respective concentrations of the phosphorus, from weak to strong, vary from 12 to 50 mg/L and from 4 to 15 mg/L in domestic wastewater (Metcalf and Eddy, 1991). Untreated effluents that contain such nitrogen and phosphate loads can be major causes of the dystrophisation especially in vulnerable ecosystems like Port-au-Prince bay (European Commission, 1998).

MATERIELS ET METHODES

Context of the ecological risk assessment

This ecological risk assessment was carried out for the general management scenario of urban wastewater observed in Haiti. This scenario envisages the discharge of urban effluents directly into the natural aquatic environment (figure 1). In the studied scenario, the ecosystem of Port-au-Prince bay has been considered as the only exposed ecosystem to the pollutants of urban effluents. An internal collector drained out these effluents flowing into the ocean. Approximately 500 m² of area with an average depth of 10 meters have been estimated as the part of the littoral directly affected by these rejections, which is equivalent to a volume of 5 000 m³ of seawater.

Figure 1 showed the conceptual framework elaborated for this ecological risk assessment. For the characterization of the effects, the following assumption was elaborated: "the discharge of of urban effluents into the Port-au-Prince bay will generate proliferation of algae and have toxicological effects on the living species (particularly the fishes and the crustaceans) of the marine ecosystem". It is based on the characterization of these effluents according to their chemical composition, i.e. the measurement of the global parameters, whose chemical oxygen demand (DCO), electric conductivity (EC), the temperature, the potential of hydrogen (pH); and of mineral pollutants (NO3

-, NH3, PO43-). The measurements taken for these various parameters are

compared with lawful limiting values for the rejection of the effluents in the urban networks of cleansing (Agence de l’eau, 1995; Commission Européenne, 1998; MATE, 1998). For Cp>Vs (CP: concentrations in pollutants in the effluents; values thresholds), the step concludes with an intrinsic danger from the effluents, whose dystrophisation related to multiple factors, and recommends to pass at the following stage of the identification of the factor determining in the dystrophisation. For any report/ratio N/P< 7 (N: nitrate weight; P: phosphate weights), according to the principle of the limiting factor, in fact the nitrates determine the effective dystrophisation of bay, having to be subjected to a detailed evaluation (Miquel, 2003).

Figure 1: Conceptual framework of the ecological risk assessment

Experimental site and intake points

Seven (7) intake points (BCP1, BCP2, BCP3, BCP4, BCP5, BCP6, BCP7) were retained on the section of the Bois de Chêne chanel arranged out of concrete, a 2 km length (figure 1), located between the intersection of Harry Truman and Oswald Durand streets (18o30' 10 "of Northern latitude and 72o21' 35" Eastern of longitude) and Capois street (18o30' 10 "of Northern latitude and 72o20' 35" of Eastern longitude). The channel is indeed the main sewer of the drainage

N/P > 7 Nitrate, limiting factor of the risk

Phosphate, limiting factor of the risk

Ecological risk affecting the balance of biogeochemical cycles of the ecosystem of Port-au-Prince bay

no

yes

Urban effluents

Risks of dystrophisation related to various factors and generating proliferation of toxic algae and aquatic macrophytes.

- Global parameters : T 0C, pH, EC, COD- Nutrients: NH3, NO3

-, PO43-.

Absence of significant risk of dystrophisation

no

yes

Identification of the limiting factor

or the risk

Cp > Vs

system of Port-with-Prince. It is approximately a 10 km length, and occurs at the Morne l’Hôpital at more than 400 m of altitude in the heights of Pétion-Ville. It is directed from the Est to the West towards of Port-au-Prince bay and curves the administrative space of the metropolitan Area of Port-au-Prince, i.e. mainly the communes of Pétion-Ville and Port-au-Prince (Léger, 2002).

Figure 2 : Expérimental Site et intake points

Sampling campaigns

Two sampling campaigns, consisting each one of 3 days of taking away, were carried out respectively during the dry season (November - March) and the rainy season (April - May). The first one took place between February 10th and March 9th, 2005 and the second between April 20th and May 11th, 2005. During these programs, 42 samples were taken at a rate of 6 per intake point. The method of flash sampling was used for the collection of the samples.

Physicochemical parameters measurements

Some physicochemical parameters such as the pH, the EC and the temperature have been measured out in situ. The pH has been measured out using an ionometer WTW pH 340ION. A conductimeter WTW-LF330 (multifunction) has been used to measure the EC. This same instrument is built-in a probe which made it possible to measure the temperature. The COD, nitrates, the ammoniacal nitrogen and the phosphates have been detected by absorption molecular spectrophotometry by means of a Spectroquant NOVA 60.

RESULTS ET DISCUSSION

Global parameters Tables 1 and 2 present the average results, the minimum and maximum, as well as the coefficients of variation (CV) obtained for certain total parameters such as temperature, pH, EC, and COD, measured on the 7 sampling stations during dry and rainy seasons.

Tableau 1: Results of dry season Stations T oC EC

(mS/cm) pH COD (mg/L) N03

- (mg/L)

NH3 (mg/L)

PO43-

(mg/L) BCP1 28,40 2,42 7,42 279,00 12,04 3,19 19,10

BCP2 29,25 2,30 7,63 277,00 1,98 2,59 27,85

BCP3 29,05 1,80 7,76 475,00 3,08 2,00 38,15

BCP4 28,55 1,94 7,61 412,00 3,08 2,00 33,10

BCP5 27,65 1,64 7,87 458,00 11,22 2,52 32,15

BCP6 29,15 8,62 8,50 571,00 12,10 0,57 56,65

BCP7 29,30 1,58 7,69 191,00 2,42 2,63 14,70

Ў 28,76 2,98 7,81 380,43 5,02 2,16 32,44

Minimum 26,40 1,16 7,42 154,00 0,88 0,23 14,40

Maximum 31,00 14,25 8,50 630,00 22,88 3,61 62,00

CV 2,09% 24,11% 4,30% 35,45% 90,90% 43,70% 47,44%

Tableau 2 : Results of rainy season

Stations T oC EC (mS/cm)

pH

COD (mg/L)

N03-

(mg/L) NH3 (mg/L)

PO43-

(mg/L) BCP1 27,10 1,78 7,65 259,00 3,52 7,61 7,50 BCP2 28,85 1,79 7,77 260,00 5,50 7,62 7,65 BCP3 28,70 1,71 7,92 361,00 4,18 8,13 12,60 BCP4 28,10 1,51 7,92 268,00 3,96 7,69 7,05 BCP5 28,00 1,54 7,95 239,00 5,50 3,06 7,05 BCP6 30,90 2,06 8,11 318,00 5,94 9,26 14,25 BCP7 31,10 1,28 7,72 223,00 4,18 2,97 3,90 Ў 28,96 1,67 7,86 275,43 4,68 6,62 8,57 Minima 27,10 1,00 7,60 130,00 0,88 2,00 2,40 Maxima 32,10 2,36 8,11 540,00 10,12 16,06 19,20 CV 5,19% 15,14% 2,12% 17,40% 20,06% 38,21% 41,77%

The temperature of the samples oscillates between 26.4 0C and 31.0 0C during the dry season, while during the rainy season it varies from 27.10C with 32.10C. It is relatively constant during various seasons, with one CV going from 2.09% to 5.19%. This situation does not represent a priori any effective danger to the tropical ecosystems of bay of Port-au-Prince, it can nevertheless or not support certain chemical and biochemical processes disturbing like the nitrification and the proliferation of the toxic brown algae (Landelout and Van Tichelen, 1960; Gay, 1983; Féray, 2000, Lacour and al., 2006). The EC of the sampled liquid effluents, variable between 1.0 and 14.25 mS/cm during the various seasons, represented an important mineralisation and confirms the presence of cations and anions like heavy metals, nitrates and phosphates probably related to urban and industrial water discharges untreated. The pH presents light variations between 2.12% and 4.30%, with values close to neutrality (7.42 - 8.50). It does not constitute a direct danger to the watery communities, insofar as it remains within the acceptable limits (5.50 and 8.50) in surface waters (Mate, 1998). On the other hand, the recorded values (higher than 7) can support the prevalence of the gas shape of the ammoniacal nitrogen, which is very toxic in particular for fish (Miquel, 2003, Lacour and al., 2006). The COD corresponds to an estimate of the oxydable matter present in water, whether this matter has mineral or organic origin. For the dry seasons, it varies through the stations and the days of taking away 130 and 630 mg/L. The average concentrations obtained in 2004, are close to certain values reported in the literature (250 to 1000 mg/L of COD) for domestic worn water untreated (Fresenius and al., 1990; Metcalf and Eddy, 1991, Grommaire-Mertz, 1998). In addition, during the rainy season the COD varies from 130 to 540 mg/L. This strong variation of the COD during the same pluviometric season translates the great diversity of the urban effluents of all kinds (Henze and al., 2001) poured in bay by the network of drainage of the city.

Summary ecological risks assessment related to nitrogen and phosphorus

Ammoniacal nitrogen

The ammoniacal nitrogen generates during the season dries a danger going from clear pollution (0.5 to 2 mg/L) to important pollution (2 to 8 mg/L). The maximum ammoniacal nitrogen concentration (16,06 mg/L) recorded during the rain season makes more than the double of the threshold of pollution important (8 mg/L) (Figure 1). Moreover, the ammonia average charge poured in bay is around 2.21 mg/L, value corresponding, in the ecotoxicological tests, with a lethal concentration (Cl50 96h) for resistant families of fish, such Cyprinidés (Garric, 1987). The

considerable increase in the ammoniacal nitrogen content recorded during the rain season can be explained by a beginning of thorough mineralisation of organic nitrogen, dependent on climatic and ecological changes considerable (Miquel. 2003)

0

2

4

6

8

10

12

14

16

18

BCP1 BCP2 BCP3 BCP4 BCP5 BCP6 BCP7

Station

Azo

te a

mm

onia

cal (

mg/

L)

Situation normale Pollution modérée Pollution nette Pollution importante Jour 1

Jour 2 Jour 3 Jour 4 Jour 5 Jour 6

Figure 1: Pollution levels by ammoniacal nitrogen during dry and rainy seasons

Forms of ammoniacal nitrogen in the samples

The ammoniacal nitrogen exists theoretically in aqueous solution in the forms of ammonium ions (NH4+) or ammonia (NH3), dependently of the pH of the solution, in accordance with the equilibrium equation: NH3 + H2O NH4

+ + OH-

On levels of pH higher than 7, balance is moved on the left, but on levels of pH lower than 7, the ion ammonium is prevalent (Metcalf and Eddy, 1991; Emmanuel and Al, 2005). The results obtained reveal a prevalence of ammonia (NH3). This dissolved gas has harmful effects for the majority of the aquatic organisms, it is very toxic for fish and, consequently, implies a danger very threatening for the integrity of the various compartments of the bay (Dyer, 2003; Miquel, 2003).

Nitrates et phosphates

The evaluation of these nutrients is made starting from the empirical data of CNRS, reported by Miquel (2003), which establish that in surface waters the risk of anthropogenic eutrophication can start at of 1 mg of NO3

-/L; as those mentioned by Rodier (1996) which foresee the phenomenon from 0,5 mg of PO4

3-/L. These standards are more restrictive but also more specific to the dystrophisation risk. Figures 3 and 4 illustrate for the dry and rainy seasons, the evolution of pollution by nitrates and phosphates, major parameters blamed in anthropogenic eutrophication.

Figure 2 : Evolution de la pollution par les nitrates

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

BCP1 BCP2 BCP3 BCP4 BCP5 BCP6 BCP7Station

Phos

phat

es (m

g/L)

Saison seche Saison pluvieuse Valeur seuil

Figure 3 : Evolution de la pollution par les phosphates

Pour les nitrates la tendance des concentrations mesurées est plutôt à la stabilité bien que moyennement moins élevées au cours de la saison des pluies par comparaison à la saison sèche (respectivement 4,64 mg/L et 5,02 mg/L), de CV respectifs = 20.06% et 90.90%. Mais dans tous les cas ou presque, au niveau de toutes les stations et au cours des deux 2 saisons, la teneur en nitrate dépasse de 1 à 12 fois la valeur limite de 1 mg/L (Miquel, 2003). Les phosphates affichent une baisse significative, probablement due à un effet de dilution au cours de la saison des pluies par rapport à la saison sèche. De 14,4 à 62,0 mg/L en saison sèche, les concentrations en ions phosphates descendent jusqu’au niveau de 2,4 à 19,2 mg/L en saison pluvieuse. Toutefois, ces concentrations restent toujours nettement au dessus du seuil de 0,5 mg/L.

Role of nitrates in the eutrofication of the bay

Under the terms of the principle of the limiting factor or Redfield ratio established between nitrates and phosphates, nitrates constitute the factor determining the growth of the algae when ratio N/P of nitrate and phosphate weight is lower than 7 (Miquel, 2003). The results of this work confirm that downstream of the watershed up to the estuarine, nitrates are generally the limiting factor of anthropogenic eutrophication (Capblancq and Dauta. 1990; Heathwaite, 1993). Phosphorus is limiting only on the upstream parts of the watershed. That is understood by a prevalence of the effluents of the urban type, rich in phosphorus, compared to those of agricultural origin richer in nitrogen, in urban wastewater (Miquel, 2003).

It consequently becomes interesting to stress that in spite of a visible phosphate ions dilution, the dystrophisation appears more effective during the rainy season. This thesis is corroborated by the fact that the nitrates, constituting the limiting factor, are potentially in raise during this season, insofar as the ammoniacal nitrogen, whose concentrations for the same season are more important, is called with nitrification, therefore to be added to nitrates.

CONCLUSION

These first results make it possible to advance that the ecological risk related to the nitrogen and phosphate substances is effective in Port-au-Prince bay, and its consequences are multiple and complex. The maximum concentrations of phosphates (62.0 mg/L) and especially of nitrates (22.88 mg/L), making respectively more than 120 and 22 times the standards, accelerate the phenomenon of dystrophisation, responsible for the disturbances in the nutrients cycles, implying a biological unbalance, and destruction of important habitats of the marine herbaria and the coral reefs, stated by Vermande and Raccurt (2001). Increase of the average concentration of ammoniacal nitrogen during the rain season, translates a nitrates load potentially in raise and, by rebound, a pronunciation of the risk of dystrophisation for this season. The slow nitrification of ammoniacal nitrogen led to conditions of anoxia of the estuarine zone. Moreover, its gas form (NH3), prevalent in the effluents, is toxic for fish. The parameters such as temperature and the pH determine less direct but considerable risks. It will now be necessary to check these first observations on effluents coming from other channels of drainage of the city. It will be also necessary to continue this work to evaluate the exposure of more organisms concerned, to estimate the prevalence of Ciguatera, intoxication related particularly to the dystrophisation, and to understand the water dilution of drainage in the bay.

Remerciements

Les auteurs présentent leurs remerciements au Programme des Nations Unies pour le Développement (PNUD) pour le financement de cette étude.

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