WATER NITRATE POLLUTION IN THE MEKONG DELTA


NHIM NITRATE TRONG NC VNG CHU TH SNG CU LONG

Abstract: Water Nitrate pollution in the Mekong River Basin . In addition to occupying a peculiar geographical situation, to being favored by its dual monsoon climatic characteristics, to being irrigated by crisscrossing river tributaries and canals draining into the South China Sea and into the Gulf of Thailand, the Mekong River Basin is also the greatest rice-producing region in Vietnam and consequently, an area of ever increasing population development. This uncontrollable human development naturally ensues urgent problems in city planning, communications, education, food supply and above all environmental pollution in which emerges the important issue of water Nitrate Pollution. The excessive use of Nitrate-containing fertilizers with an aim to boost agricultural production, the traditional unsanitary ways of human and animal wastes disposal, the slow oxidation of underwater organic material in inundated areas, are the main sources of Nitrate pollution in the Basin. Nitrate under the form of its water soluble basic salt K, Na, Mg, Ca readily infiltrates soils and underground water and when ingested by humans, especially infants, can be harmful. For this reason, the maximum allowable amount of Nitrate in water is 45 mg/L, the water biochemical oxygen demand BOD should not exceed 25 mg/L and the water total dissolved solids TDS not reach the value of 20. The transformation reaction of Nitrate into Nitrite in the human body by bacteria leads to the rapid combination of Nitrite with blood Hemoglobin and the formation of Methemoglobin, a substance devoid of Oxygen-carrying capacity, thereby reducing the Oxygen supply to body tissues. According to USEPA, Nitrate water pollution has a profound impact on pregnant women with damage to fetal nervous and cardiovascular system, prematurity and low birth-weight.. The prevention and treatment of nitrate-polluted water in the Mekong River Basin with its demographic explosion are more than ever urgent and through his remedial proposals, the author would like to awaken the awareness and concern of all the inhabitants in the Basin on the current and future impact of this problem. Among the Nitrate pollution treatment methods that had been presented and taking into consideration the cost-effectiveness and feasibility of each of these methods, the author suggested the ion-exchange Chlorination of water and the injection of vegetable oil into the Nitrate polluted water bodies and underground water to promote the transformation of Nitrate into Nitrogen. A series of preventive measures such as the adequate storage of fertilizers, the location of water supply sources away from Nitrate-containing materials, the remodeling of water wells and latrines, associated with the sanitation education of the population, has also been proposed.

Vng Chu Th Sng Cu Long l va la ln nht Vit Nam, rng 39.574.000 mu ty, chim 12% tng din tch Vit Nam. Vi hnh th mt bn o c ba mt u gip bin, Chu Th Sng Cu Long c mt sc thi kh hu rt c bit, mt mt chu tc ng ca h thng bin pha ng v Ty, mt mt chu nh h߷ng ca thy triu khc nhau: pha Ty gip vi Vnh Thi Lan v pha ng vi Bin Nam Hi. V vy, vng ny c mt c im him thy l trn cng mt chu th c nhng con sng chy ngc chiu nhau: sng ra bin pha ng, sng ra bin pha Ty v nhng sng khc ni lin bin ng v Ty.

Thm vo , Chu Th Sng Cu Long cn chu nh h߷ng ca gi ma Ty Nam t thng nm n thng m߶i mt (ma ma); v ma kh c gi ng Bc t thng m߶i hai n thng t. Lng ma trung bnh khong 2.400 mm pha Ty v 1.600 mm pha ng. Vng ny l vng duy nht ng Nam khng b tc ng trc tip ca ging bo nhit i, do kh hu t߽ng i n nh v c s gi nng trung bnh hng nm l 2.400 n 2.800 gi, rt thun li cho vic trng trt v chn nui.

c l l l do dn s pht trin nhanh chng t 2.9 nm 1954 n 15.5 trong nm 1995 v cng v vy ny sinh ra mt s vn phc v cho nhu cu i sng khng theo kp vi mc gia tng dn s nh vic pht trin th, nhu cu giao thng, gio dc, l߽ng thc v nht l vn mi sinh v nhim mi tr߶ng, trong n߾c sinh hot cho dn chng c tm quan trng hng u. Trong phm vi bi vit hm nay, ng߶i vit xin trnh by vn nhim n߾c sinh hot trong vng, c bit l nhim nitrate.

nhim nitrate trong ngun n߾c l mt u t rt ln, nht l trong cc vng sn xut la go v nng phm cn n vic x dng nhiu phn bn nh vng Chu Th Sng C Long. Bn cht ca nitrate (NO3-) t n khng nh h߷ng g n sc khe ca con ng߶i v th vt; nhng khi xm nhp vo c th con ng߶i, Nitrate c th bi6n dng thnh Nitrite (NO2-) v d߾i dng ny c th gy t vong cho tr con d߾i su thng, tr߾c khi h thng tiu ha ca tr em c cu to hon chnh.

V l do , vn Nitrate cn phi c lu tm nhiu hn na trong i sng hng ngy. Nitrate th߶ng hin din d߾i dng kim (Kalium v Natrium), kim th (Magnesium v Calcium), Nhm, St v mt s kim loi nng khc... Nitrate ha tan d dng trong n߾c, thm thu mau vu lng t v mch n߾c ngm. Nng Nitrate cho php c trong n߾c ung l 45mg/L (tiu chun ca B KHCN & MT 1995).

nhng vng c nhiu Nitrate, n߾c c nhu cu sinh ha oxy (Biochemical Oxygen Demand - BOD) cao ty theo c߶ng xm nhp ca Nitrate. Nu lng BOD > 25 mg/L theo tiu chun M, th c th nh h߷ng n sc khe con ng߶i v th vt. S hin din ca Nitrate cng lm tng lng cc cht rn ha tan trong n߾c (Total Dissolved Solids - TDS). Nu lng TDS > 20 (tiu chun VN 1995), n߾c tr thnh nguy hi n sc khe con ng߶i.

Nitrate n t u ? V nh h߷ng ca n trn con ng߶i v th vt nh th no ?

Ь tr li hai cu hi trn, nhn li bi cnh Vit Nam, c bit Vng Chu Th Sng Cu Long l ni dn chng sng chen chc gia hai Sng Tin v Hu, chen ln v s kinh rch chy ngang dc chng cht trong sut m߶i mt tnh trong vng. Pha Bc Sng Tin gm tnh аng Thp, Long An, Tin Giang; gia hai sng gm Bn Tre, Tr Vinh, Vnh Long v sau cng pha Ty Sng Hu gm tnh An Giang, Cn Th, Sc Trng, Kin Giang v Minh Hi. Mt kinh rch t 0.4 n 0.6 Km/Km2, c cao t 0.0 m n 1.5 m so vi mt bin. Уc bit vng trung tm Chu Th c ni thp hn trn mt bin nhiu v l vng c thot thy rt km. Dn chng trong vng a s theo ngh nng v sn xut la go l ngun li chnh.

C thin nhin ln con ng߶i l nguyn nhn to ra nhim nitrate vi nhng tnh cht c bit nh sau:

Phn bn cho nng nghip cha ngun Nitrate chnh, s lng Nitrate khng c cy c hp thu ht s tn ti trn mt t hoc theo ߶ng n߾c thm thu xm nhp vo mch n߾c ngm. Ь c mt khi nim v lng phn bn c x dng vng trn theo thng k nm 1965, lng phn bn c x dng trung bng l 63KG/Mu/Ma v cho n nm 1990 dn chng x dng trung bnh 74 KG/Mu/Ma phn bn. Tuy khng c s liu chnh xc v nng xut la trong hai giai on k trn nhng vi nng xut khong 8 Tn/Mu/Ma lacho nm 1965, thit ngh nng xut trong nm 1990 chc chn khng tng thm ( M ti Iowa trong vng hai m߽i nm t 1960 n 1980 lng phn bn tng hn 80%, nhng mc sn xut bp ch tng c 10% m thi !). Cc ni b nhim Nitrate theo ti liu ca L Huy B l h thng kinh Ci Sn, kinh Tm Ngn v T Gic Long Xuyn (Mi Tr߶ng - L Huy B - Nh Xut Bn KHKT 1997 - VN).

Cc iu kin thin nhin t tri ma n hin tng Oxid ha cc hp cht hu c trong thin nhin hay cc cht hu c ph thi t cc sinh hot hng ngy ca con ng߶i. Trong ma ma vng nng thn, nng Nitrate c th ln n 80 mg/L.

Phn ng߶i v phn sc vt cng l mt ngun Nitrate quan trng. Vng Chu Th Sng Cu Long a s dn chng i i tin trn sng hoc trn ng trng cng nh trn cc h nui c... to iu kin cho vic nhim Nitrate trm trng, nht l v ma n߾c l.

Уc bit trn Vng Chu Th Sng Cu Long, Nitrate c to thnh do cc phn ng oxid ha chm cc hp cht hu c nh cy ci, t v cc cht khc trm tch lu ngy d߾i t.. do b dm su ߾i mt n߾c.

Cn c trn cc ngun to ra Nitrate k trn, con ng߶i d phn ng k khng km thin nhin vo vic to ra nhim ha cht ny. Theo ߾c tnh ca US Geological Survey th trn t M, nhim Nitrate do con ng߶i to ra l 50% v cc nguyn nhn khc gm c thin nhin l 50%. Nhnh trong iu kin Vit nam, thit ngh con ng߶i gp phn vo vic nhim trn nhiu hn ߾c tnh ca Hoa k !

Vic Nitrate nh h߷ng n con ng߶i c ghi nhn nh sau:

Theo khuyn co ca UNICEF Lin Hip Quc, nitrate trong ngun n߾c l mt nguy c nh h߷ng n sc kho ca con ng߶i v th vt, nht l tr con d߾i su thng to nn Hi Chng Tr Xanh (Blue Baby Syndrome) c tn khoa hc l methemoglobin huyt (Methe moglobinemia). Nitrate khi xm nhp vo c th tr em c cc vi khun trong c quan tiu ha hon chuyn thnh Nitrite v cht sau ny hp vi Huyt Cu T (Hemoglobin) trong mu to thnh Methemoglobin, do gim thiu lng Huyt Cu T v kh nng chuyn ch Oxygen ca cht ny trong c th. Do s thiu Oxygen trong c th, da i mu xanh do c tn l Hi Chng Tr Xanh.

Tr em d b nhim Nitrate hn ng߶i ln. Яi vi tr em trn su thng, bao t bt u tit ra Acid Chlorhydric do tiu dit c cc vi khun trong bao t v chn ng s hon chuyn Nitrate thnh Nitrite. S t vong do hi chng ny t߽ng i him, nhng cc di hi lu di cho n hm nay vn cn trong vng nghin cu. Tuy nhin mt s tr߶ng hp ung th ߶ng tiu ha c chng minh l do s tim nhim Nitrate trong thi gian di (Kross B.C. - Am. J. Public Health 83:270-272-1993).

C quan Bo V Mi Tr߶ng (USEPA) cng khuyn co dn chng bit l hai ngun nguy hi cn bn trong n߾c sinh hot hng ngy l Vi Khun v Nitrate. Khi ph n mang thai dng n߾c cha nhiu Nitrate, thai nhi s b nh h߷ng. Mt s pht hin c kim chng nh sau: h thng thn king ca tr so sinh b o ln, mm ung th c t trong bo thai, tim b tn th߽ng, sinh thiu thng v khng cn lng.

ng tr߾c him ha Nitrate trn, vi mt dn chng trong vng gp i so vi mt ca c n߾c (385 ng߶i/Km2 v 209 ng߶i/Km2 theo thng k nm 1992), vi t l sinh sn mc 2.2% v vi d kin tng tr߷ng dn s t n 18 triu nm 2000 (theo thng k 1995, dn s trong vng l 16.5 triu), v a s dn chng trong vng la tui thiu nin v thanh nin, nu khng c bin php phng nga hay gim thiu lng Nitrate nhim ngun n߾c sinh hot hin ti tr߾c mt....th t߽ng lai sc kho dn chng Vit Nam s b nh h߷ng kh nng n.

Tuy c kh khn v tr ngi trong vic suy tm d kin v nghin cu Vit Nam, ng߶i vit xin ng gp vi kin sau y v vn trn, ng hu dng ln ting chung bo ng n ng bo Vng Chu Th Sng Cu Long.

cc n߾c tin tin nh M, mt s bin php x l Nitrate chng t rt hu hiu, nhng chi ph x l rt cao v i nhiu k nng chuyn mn: l cc ph߽ng php chng ct, trao i ion v thm thu ngc (reverse osmosis)

Ph߽ng php chng ct v kt t i hi nng lng ln lao v h thng chng ct quy m, do kh p dng trong iu kin ca dn chng Vng Chu Th.

Ph߽ng php trao i ion bng Chlor ha n߾c b nhim v ion Chlor s thay th ion Nitrate trong n߾c. Ph߽ng php ny c ba li im l: va dit vi khun trong n߾c va thay th Nitrate v lm gim thiu lng cht rn ha tan trong n߾c (TDS). V tnh kh thi ca ph߽ng php ny, thit ngh c th thc hin c, v Chlor c sn xut trong n߾c v Chnh Quyn c th gp sc thit b h thng n gin em Chlor vo ngun n߾c sinh hot.

Ph߽ng php xuyn thm thu i hi chuyn vn n߾c cn x l xuyn qua h thng p sut v mng thm thu (t tin v khng t sn xut trong n߾c c), do ch lit k ra y vi tnh cch thng tin v tham kho hn l mt ph߽ng php ngh x l Nitrate Vit Nam.

Gn y nht B Nng Lng M (US Dept of Energy) c cng b mt ph߽ng php mi v ang c p dng M t u nm 1996, l ph߽ng php dng du thc vt kh Nitrate ! Ph߽ng php ny c bit c dng kh Nitrate nhim trong cc mch n߾c ngm. Bm du thc vt vo mt t chung quanh ngun n߾c nh ging, ao, h, sui.... Khi thm thu su vo t chung quanh v ty theo iu kin cu to th nh߷ng, du s tch t nhiu lp khc nhau. Khi n߾c cha Nitrate i xuyn qua lp du trn, cc vi sinh vt trong thin nhin s hp th Carbon trong du v pht trin mnh bin Nitrate thnh kh Nitrogen, kh ny s c hp th li trong n߾c. V n߾c c kh Nitrate s theo dng chy m i vo ao h ging...tr li.

Vi ph߽ng php ny ta c th x l Nitrate t nng trn 800 mg/L xung thp hn tiu chun cho php l 45 mg/L.

Ph߽ng php sau cng trn y c v kh thi hn ht v du thc vt l loi du n khng c hi t hy trong lng t sau mt thi gian, gi r v c sn xut khp min Nam. Mt im li khc ca ph߽ng php ny l mt s nhim hu c trong n߾c nh xng du v mt s cht dung mi dng trong thuc tr su ry, thuc dic c di cng c hp th theo.

Trn y l bn gii php ngh v vic x l nhim Nitrate trong ngun n߾c sinh hot. Tuy nhin phng nga nhim hay gim thiu nhim vn l mt ph߽ng php ti u tr߾c khi phi x l nhim.

Mt khc cc ngh sau y c tnh cch thit thc v nm trong kh nng ca mi ng߶i dn ng hu c th bo v chnh mnh v th h t߽ng lai ca Vit Nam.

  1. Tr߾c ht, v tr cc ngun n߾c ung (ging, h, ao, sui...) phi trn vng cao, v t nht phi cch xa cc chung nui sc vt cnh nh cc h phn cc xa khong 50 m.
  2. Bo qun tht k cc bao phn ha hc v cch xa ngun n߾c. Nn lu ch mt vi gram phn bn cng c th lm nhim n߾c c.
  3. Ging n߾c phi c thnh cao hn mt t cho n߾c trn mt t khng trn vo c.
  4. Cc h x gia nh phi c bo qun ng tiu chun v sinh v phi xa cch ngun n߾c.
  5. Cn phi t chc vic gio dc ng߶i dn min Chu Th Sng Cu Long v cc tai hi ca thi quen i tin trn sng hay cc h nui c trnh nhim.
  6. H߾ng dn cho ng߶i dn x dng ng cch v ng liu lng thuc tr su ry, thuc dit c di, phn bn.... Cn nhn mnh rng bn nhiu phn cha hn lm tng nng sut thu hoch m c th lm cho t cha thm nhiu ha cht d tha, v cc cht ny xm nhp vo ngun n߾c sinh hot.
  7. Sau ht ph bin n ng߶i dn nim thm canh phi phi hp vi lun canh v l ph߽ng php tt hn ci to t v tng nng sut thu hoch so vi vic tng thm lng phn bn.

Vi bin php gin d c ngh trn y v vi s lu tm thc hnh ng ca tt c, hy vng nn nhim Nitrate trong ngun n߾c sinh hot s c phngcng nh gim thiu v t n tiu chunchp nhn c.
Mai Thanh Truyet
Orange, CA 10/97

The author, Mai Thanh Truyet Ph.D. is currently:

  • QA Manager at Weck Laboratories Inc., Industry, CA.
  • Laboratory Manager and Leachate Treatment Plant Manager at BKK Laboratories, West Covina, CA.
  • Specialist in Toxic and Hazardous Waste Management and Air Monitoring.
For comments and questions, please contact Dr Mai Thanh Truyet at: Mttruyet@aol.com


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