N., and Bakry, N. M. (2006)

Abou-Arab, A. A. K. and Abou Donia, M. A. (2001). Pesticide residues in some Egyptian spices and medicinal plants as affected by processing. Food Chemistry 72: 439-445.
Chem Codes: Chemical of Concern: DZ Rejection Code: FATE.

Pesticide residues were determined in Egyptian spices and medicinal plants. For this purpose, a total of 303 samples, which represent 20 different plants were collected from sources in Egypt and several shipments All the collected samples were analyzed for the determination of organophosphorus and organochlorine residues. The obtained results showed the predominance of malathion in most of the analyzed samples. The detected concentrations of it in jews mallow, dill, celery, tea, caraway, chamomile and saffron exceeded the maximum permissible levels (MPLs), as did the concentrations of dimethoate in caraway and chamomile samples. Low levels of profenofos, pirmiphos-methyl, chloropyrifos. parathion and diazinon were determined in the analyzed samples. Residues of lindane, aldrin, dieldrin, DDT, chlordane and endrin in chamomile samples exceeded the MPLs. Residues of aldrin and dieldrin in karkade were higher than the MPLs, as was chlordane in peppermint. Residues were not detected in the watery extract when the medicinal plant was boiled in water. Also, immersing the plants in hot water transferred some pesticide residues to the aqueous extract.

ABOU-ARAB A AK (1999). Behavior of pesticides in tomatoes during commercial and home preparation.
Chem Codes: Chemical of Concern: DZ Rejection Code: FATE.

BIOSIS COPYRIGHT: BIOL ABS. Monitoring of pesticide residues in Egyptian tomatoes and its products was studied. The average contents of HCB, lindane, dieldrin, heptachlor epoxide and DDT derivatives were detected at levels 0.009, 0.003, 0.006, 0.008 and 0.083 mg/kg, respectively. On the other hand, the levels of dimethoate, profenofos and pirimiphos-methyl were 0.461, 0.206 and 0.114 mg/kg, respectively. In ketchup and paste samples, most organochlorine and organophosphorus pesticide residues were not detectable. The distr eling, were necessary to remove pesticide residues in the skin. Cooking of tomatoes (including processing tomato to paste) helped to eliminate most pesticide residues from contaminated tomatoes. Biochemistry/ Food Technology/ Poisoning/ Animals, Laboratory/ Biophysics/ Plants/Chemistry/ Plants

ABOU-ARAB AAK, KAWTHER, M. SOLIMAN, EL TANTAWY ME, BADEAA, R. ISMAIL, and KHAYRIA, N. (1999). Quantity estimation of some contaminants in commonly used medicinal plants in the Egyptian market. FOOD CHEMISTRY; 67 357-363.
Chem Codes: Chemical of Concern: DZ Rejection Code: HUMAN HEALTH.

BIOSIS COPYRIGHT: BIOL ABS. Pesticide residues, heavy metal contents and aflatoxins were estimated in five medicinal plants frequently used by both infants and adults (peppermint, chamomile, anise, caraway and tilio). Samples were collected from different sources in the Egyptian market. Results showed that malathion, dimethoate and profenofos predominated in most of the analysed samples. On the other hand, the lowest mean levels were detected with aldrin, dieldrin, chlordane and lindane. Chlorpyrifos, parathion, diazinon and endosulfan were not detectable in most of the samples under investigation. The results indicated that some of the collected samples contained some types of organophosphorus and orgnochlorine pesticide residues, within the limits of The Egyptian Organization for Standardization and Quality Control (EOS) maximum limits for pesticide residues on medicinal aromatic plants (1991) and Pharmeuropa (19 93). Heavy metal contents in the collected samples, i.e. Fe, Cu, Mn, Zn, Pb, Cd, Cr, Co, Sn and Ni,were found at different levels. The highest mean levels of Pb, Zn, Cu, and Fe were found in chamomile flower samples, while those of Cd, Cr and Mn, were detected in peppermint and of Ni, Co and Sn in caraway samples. The results also showed that the most frequently isolated fungi were penicillium sp., A. niger and Fusarium sp. Nevertheless, the finding of natural mycotoxin contamination was negative in all samples. Biochemistry/ Poisoning/ Animals, Laboratory/ Pharmacognosy/ Plants, Medicinal/ Herbicides/ Pest Control/ Pesticides/ Plants/ Mitosporic Fungi/ Plants/ Plants/ Coleoptera

Abu-Qare, A. W. and Abou-Donia, M. B. (2001). Inhibition and Recovery of Maternal and Fetal Cholinesterase Enzyme Activity Following a Single Cutaneous Dose of Methyl Parathion and Diazinon, Alone and in Combination, in Pregnant Rats. J.Appl.Toxicol. 21: 307-316.

EcoReference No.: 85502

Chemical of Concern: DZ,MP; Habitat: T; Effect Codes: BCM; Rejection Code: NO ENDPOINT(DZ).

Adachi, K., Ohokuni, N., and Mitsuhashi, T. (1984). Simple analytical method for organophosphorus pesticide determination in unpolished rice, using removal of fats by zinc acetate. Journal of the Association of Official Analytical Chemists [J. ASSOC. OFF. ANAL. CHEM.] 67: 798-800.

Chem Codes: Chemical of Concern: DMT Rejection Code: METHODS.

A rapid and simple method is developed for the determination of organophosphorus pesticides in unpolished rice. The new method incorporated acetonitrile-water (1 + 1) extraction, removal of fats by zinc acetate, and further cleanup on an activated charcoal chromatographic column. The higher fatty acids in the extract react rapidly with zinc acetate to form insoluble zinc carboxyltes, which precipitate. Additional interferences were cleaned up on an activated charcoal chromatographic column, and organophosphorus pesticides adsorbed on the activated charcoal were eluted with acetone-hexane. Dimethoate is not retained on the activated charcoal and must be extracted with dichloromethane from the first acetonitrile-water eluate. Pesticides are measured by flame photometric gas chromatography. Recoveries from 50 g unpolished rice samples fortified with 5-50 mu g diazinon, 6-30 mu g parathion, 8-40 mu g fenitrothion and IBP, 10-50 mu g dimethoate and fenthoate, 20-100 mu g malathion, ro 40-100 mu g EPN ranged from 75.7 to 95.8%. Classification: X 24221 Toxicity testing; X 24120 Food, additives & contaminants pesticides/ pesticides (organophosphorus)/ residues/ Oryza sativa/ zinc acetate/ determination

Adachi, K., Ohokuni, N., and Mitsuhashi, T. (1984). Simple analytical method for organophosphorus pesticide determination in unpolished rice, using removal of fats by zinc acetate. Journal of the Association of Official Analytical Chemists [J. ASSOC. OFF. ANAL. CHEM.]. Vol. 67, no. 4, pp. 798-800. 1984.
Chem Codes: Chemical of Concern: DZ Rejection Code: METHODS.

ISSN: 0004-5756

Descriptors: pesticides
Descriptors: residues
Descriptors: Oryza sativa
Abstract: A rapid and simple method is developed for the determination of organophosphorus pesticides in unpolished rice. The new method incorporated acetonitrile-water (1 + 1) extraction, removal of fats by zinc acetate, and further cleanup on an activated charcoal chromatographic column. The higher fatty acids in the extract react rapidly with zinc acetate to form insoluble zinc carboxyltes, which precipitate. Additional interferences were cleaned up on an activated charcoal chromatographic column, and organophosphorus pesticides adsorbed on the activated charcoal were eluted with acetone-hexane. Dimethoate is not retained on the activated charcoal and must be extracted with dichloromethane from the first acetonitrile-water eluate. Pesticides are measured by flame photometric gas chromatography. Recoveries from 50 g unpolished rice samples fortified with 5-50 mu g diazinon, 6-30 mu g parathion, 8-40 mu g fenitrothion and IBP, 10-50 mu g dimethoate and fenthoate, 20-100 mu g malathion, ro 40-100 mu g EPN ranged from 75.7 to 95.8%.
Language: English
English
Publication Type: Journal Article
Classification: X 24221 Toxicity testing
Classification: X 24120 Food, additives & contaminants
Subfile: Toxicology Abstracts

Adams, P. B. and Wong, J. A. L. (1991). The Effect of Chemical Pesticides on the Infection of Sclerotia of Sclerotinia minor by the Biocontrol Agent Sporidesmium sclerotivorum. Phytopathology 81: 1340-1343.

EcoReference No.: 70656

Chemical of Concern: PNB,CBL,CHD,DZ; Habitat: T; Effect Codes: PHY; Rejection Code: TARGET(DZ).

Adlung, K. G. (1957). The Toxicity of Insecticidal and Acaricidal Agents to Fish (Zur Toxizitat Insektizider und Akarizider Wirkstoffe fur Fische). Naturwissenschaften 44: 471-472.

EcoReference No.: 935

Chemical of Concern: DZ,HCCH,MLN,PYN,RTN; Habitat: A; Effect Codes: MOR; Rejection Code: NO CONTROL,FOREIGN(ALL CHEMS).

Adonaylo, V. N. and Oteiza, P. I. (1999). Pb2+ promotes lipid oxidation and alterations in membrane physical properties. Toxicology 132: 19-32.

Chem Codes: Chemical of Concern: DZ Rejection Code: NO TOX DATA.

Experimental evidence suggests that cellular damage mediated by oxidants could be involved in the pathology associated with lead (Pb) toxicity. We investigated the effect of Pb2+ on lipid oxidation in liposomes using different initiators. In the presence of Fe2+, Pb2+ (12.5-200 [mu]M) stimulated lipid oxidation in phosphatidylcholine:phosphatidylserine-containing liposomes, measured as 2-thiobarbituric acid-reactive substances (TBARS) and conjugated dienes. This stimulatory effect depended on the presence of membrane negative charges and on bilayer integrity. Pb2+ did not stimulate TBARS formation in the presence of 25 mM 2,2′-azo-bis (2,4 dimethylvaleronitrile (AMVN) and 2,2′ azobis (2-amidinopropane) (AAPH). Pb2+ significantly stimulated TBARS production and NADH oxidation in the presence of photoactivated rose Bengal. The use of specific inhibitors indicated that several reactive oxygen species were involved in the pro-oxidant action of Pb2+. Pb2+ (12.5-200 [mu]M) caused membrane lateral phase separation and this effect was positively correlated with its capacity to stimulate Fe2+ and rose Bengal-initiated TBARS production. Pb2+ could bind to the membrane and act to stimulate lipid oxidation by causing changes in membrane physical properties. Through this mechanism Pb2+ would favor the propagation of lipid oxidation. By causing lateral phase separation and/or by increasing lipid oxidation rates, Pb2+ could be cytotoxic by altering membrane-related processes. Lead/ Lipid oxidation/ Iron/ Free radicals/ Phase separation

Ageda, Saori, Fuke, Chiaki, Ihama, Yoko, and Miyazaki, Tetsuji ( The stability of organophosphorus insecticides in fresh blood. Legal Medicine In Press, Corrected Proof.
Chem Codes: Chemical of Concern: DZ Rejection Code: FATE.

We investigated the stability of 14 organophosphorus insecticides: dichlorvos, fenitrothion, cyanophos, malathion, phenthoate, methidathion, dimethoate, thiometon, isoxathion, diazinon, trichlorfon, EPN, acephate and sulprofos, in fresh blood. The organophosphorus compounds, except for sulprofos, decomposed over time at 37 [deg]C, with varying decomposition speed for each compound. Methyl phosphate types (dichlorvos) decomposed most rapidly, followed by methyl thiophosphate types (fenitrothion and cyanophos) and methyl dithiophosphate types (methidathion, dimethoate and thiometon). Methyl thiophosphate types decomposed faster than ethyl thiophosphate types (isoxathion and diazinon). Of the five methyl dithiophosphate type insecticides (malathion, phenthoate, methidathion, dimethoate and thiometon), the compounds with a carboxylic ester bond (malathion and phenthoate) decomposed faster than the others. Compounds left standing at 37 [deg]C decomposed faster than those left standing at 4 [deg]C. Temperature has a great effect on the decomposition of organophosphorus insecticides in blood. However, the order of the decomposition speeds of each compound was approximately the same at different temperatures. In cases of suspected organophosphate poisoning, it should be considered that the blood concentration of the compound might decrease during the postmortem interval. Poisoning/ Organophosphates/ Stability/ Blood

AHMAD, M. (1990). The effect of PB and DEF synergists on the toxicities of endosulfan, diazinon and monocrotophos in Heliothis armigera. J PLANT PROT TROP; 7 117-122.
Chem Codes: Chemical of Concern: DZ Rejection Code: MIXTURE.

BIOSIS COPYRIGHT: BIOL ABS. The synergistic effect of piperonyl butoxide and DEF was studied for endosulfan, diazinon and monocrotophos in Heliothis armigera (Hubner). Endosulfan was synergised around two-, four- and sevenfold with the application of PB, DEF and PB + DEF respectively at LD50 level. The toxicity of diazinon was mildly increased by PB (x2) at LD50 but not by DEF. Both the synergists were however found ineffective in synergising monocrotophos. Biochemistry/ Poisoning/ Animals, Laboratory/ Herbicides/ Pest Control/ Pesticides/ Arachnida/ Entomology/Economics/ Plants/ Arachnida/ Entomology/Economics/ Insecticides/ Pest Control/ Pesticides/ Animal/ Disease/ Insects/Parasitology/ Lepidoptera

Ahmad, M. H. and Vekataraman, G. S. (1973). Tolerance of Aulosira fertilissima to Pesticides. Curr.Sci. 42: 108 (ABS).
Chem Codes: Chemical of Concern: MCPB,MCPA,HCCH,PRN,EN,CBL,DZ,PPN Rejection Code: ABSTRACT.

Akasu, T. and Karczmar, A. G. (1980). Effects of anticholinesterases and of sodium fluoride on neuromyal desensitization. Neuropharmacology 19: 393-403.

Chem Codes: Chemical of Concern: DZ Rejection Code: IN VITRO.

Desensitization of amphibian neuromyal junction was obtained by either repetitive, brief (2 msec) iontophoretic pulses of acetylcholine (ACh) or by a prolonged (40 sec) iontophoretic application of ACh. When ACh was applied repetitively, ACh potentials diminished gradually at a rate dependent on ACh pulse frequency; the recovery time constant amounted to approximately 7 sec following 30 sec of brief ACh pulses applied at 20 Hz. In the case of prolonged, 40 sec ACh pulses, repolarization occurred within the duration of the pulse. Subsequent test (2 msec) pulses of ACh showed a diminished endplate response.Anticholinesterase drugs, the organophosphorus tetraethylpyrophosphate (TEPP) and the carbamate, neostigmine, markedly accelerated desensitization. This occurred even when the iontophoretic current was decreased following anticholinesterase treatment in order to generate ACh potentials similar in amplitude to those recorded prior to the treatment. These and additional results indicated that anticholinesterases exert a direct, desensitizing effect independently of the possibility of their causing accumulation of iontophoretically applied ACh.Sodium fluoride (NaF) employed in concentrations of 0.1 to 5 mM, significantly delayed the onset of desensitization whether the latter was induced by repetitive or prolonged pulses of ACh; it also accelerated the recovery of the endplate from desensitization. At concentrations ranging from 0.05 to 2 mM, NaF also antagonized the acceleration of desensitization induced by either TEPP or neostigmine; in the combined presence of the anticholinesterase and NaF, the rate constant of desensitization approximated to that recorded under control conditions. This action by NaF was exerted after prolonged (30 min) TEPP treatment; thus, this effect was not due to the reactivating potential of NaF. Repetitive (at 50 Hz) indirect stimulation of the endplate produced progressive diminution of the EPP's, with a plateau occurring at 60 sec. This was concomitant with marked diminution of the response to test pulses of ACh and a slight decrease in the quantal content of the EPP's; thus, it was not due to diminution of the release of ACh. The rate of this phenomenon was markedly increased by anticholinesterases and markedly decreased by NaF.It is emphasized in the Discussion that the antidesensitizing action of NaF does not depend on its chelation of Ca2+ and that it may be due to the direct action of NaF on the recentor.

AKEY WC, RUSSELL, T., ALFORD, C., MORRISON, T., and DENNING, M. (1997). Will the toad croak? An endangered species decision case. JOURNAL OF NATURAL RESOURCES AND LIFE SCIENCES EDUCATION; 26 148-156.
Chem Codes: Chemical of Concern: DZ Rejection Code: NO TOX DATA.

BIOSIS COPYRIGHT: BIOL ABS. In 1992, the USEPA proposed a ban on the use of 43 pesticides in a large portion of Albany County, Wyoming. The ban was intended to protect the habitat of an endangered species, the Wyoming toad (Bufo hemiophyrs baxteri), as required by the Endangered Species Act of 1973. For many years, portions of Albany County that included Wyoming toad habitat had been routinely sprayed with insecticides to control mosquitoes. Residents were concerned that without adequate mosquito control, recreation, tourism, agriculture, public health, and property values could be impacted. A task force comprised of local residents of diverse backgrounds and viewpoints was appointed in 1992 by the governor of Wyoming and Albany County commissioners to consider how best to (i) protect the Wyoming toad and aid its recovery, and (ii) maintain effective mosquito control. The goal of the group was to submit an alternative proposal to the U.S. Fish and Wildlife Service and to the USEPA that would meet Conservation of Natural Resources/ Animals, Wild/ Conservation of Natural Resources/ Ecology/ Herbicides/ Pest Control/ Pesticides/ Arachnida/ Entomology/Economics/ Insecticides/ Pest Control/ Pesticides/ Amphibia/ Anura

AKHTAR, S., MISBAHUDDIN, SIDDIQUI, P. MH, and BALOCH UK (1998). Effect of neem cake on persistence of diazinon and endosulfan in paddy soil. PESTICIDE SCIENCE; 52: 218-222.
Chem Codes: Chemical of Concern: AZD Rejection Code: FATE.

BIOSIS COPYRIGHT: BIOL ABS. Experiments were carried out to study the influence of two types of neem cake (solvent-extracted, NC-I and expeller-extracted, NC-II) on the persistence in soil of diazinon and endosulfan applied as commercial formulations. It was found that both types of neem cake applied at 10, 20 or 30 g ha-1 prolonged the period of degradation as compared with soils without neem cake amendment, and hence increased the persistence of the insecticides. There was little difference in the effect of the two types of neem cake. Treatment of the soil with insecticide 10 days after amendment with neem cake did not lead to any increase in persistence; for a good response, treatment of soil with insecticide and with neem cake must be done at the same time. Biochemistry/ Soil/ Herbicides/ Pest Control/ Pesticides

AKHTAR, S., MISBAHUDDIN, SIDDIQUI, P. MH, and BALOCH UK (1998). Effect of neem cake on persistence of diazinon and endosulfan in paddy soil. PESTICIDE SCIENCE; 52 218-222.
Chem Codes: Chemical of Concern: DZ Rejection Code: FATE.

BIOSIS COPYRIGHT: BIOL ABS. Experiments were carried out to study the influence of two types of neem cake (solvent-extracted, NC-I and expeller-extracted, NC-II) on the persistence in soil of diazinon and endosulfan applied as commercial formulations. It was found that both types of neem cake applied at 10, 20 or 30 g ha-1 prolonged the period of degradation as compared with soils without neem cake amendment, and hence increased the persistence of the insecticides. There was little difference in the effect of the two types of neem cake. Treatment of the soil with insecticide 10 days after amendment with neem cake did not lead to any increase in persistence; for a good response, treatment of soil with insecticide and with neem cake must be done at the same time. Biochemistry/ Soil/ Herbicides/ Pest Control/ Pesticides

Al-Attar, H. J. and Knowles, C. O. (1982). Diazinon Uptake, Metabolism, and Elimination by Nematodes. Arch.Environ.Comtam.Toxicol. 11: 669-673.

EcoReference No.: 46889

Chemical of Concern: DZ; Habitat: T; Effect Codes: ACC; Rejection Code: NO ENDPOINT(DZ).

AL-AZAWI AF (1986). FIRST REPORT ON THE SCREENING OF INSECTICIDES AGAINST DASYNEURA-OLEAE DIPTERA CECIDOMYIDAE AN IMPORTANT PEST OF OLIVE TREES IN IRAQ. HORTSCIENCE 21: 731.

Chem Codes: Chemical of Concern: OMT Rejection Code: ABSTRACT.

BIOSIS COPYRIGHT: BIOL ABS. RRM ABSTRACT LEAF GALL DIAZINON 30 NOGOS 90 EKALUX 450 MOSTAQUICK 600 ANTHIO 700 FOLIMAT 1800 CROP INDUSTRY Congresses/ Biology/ Biochemistry/ Fruit/ Nuts/ Tropical Climate/ Herbicides/ Pest Control/ Pesticides/ Arachnida/ Entomology/Economics/ Fruit/ Nuts/ Arachnida/ Entomology/Economics/ Insecticides/ Pest Control/ Pesticides/ Plants/ Diptera

Al-Mohanna, F. A. and Hallett, M. B. (1990). “Clamping” actin in polymerized form in electropermeabilized neutrophils inhibits oxidase activation. Biochemical and Biophysical Research Communications 169: 1222-1228.
Chem Codes: Chemical of Concern: DZ Rejection Code: IN VITRO.

Electro-permeabilized neutrophils take-up small membrane-impermeant molecules into their cytoplasm, yet retain the ability to activate their oxidase and to transiently polymerize actin in response to f-met-leu-phe (fmlp). Using this system phalloidin was introduced into the cytosol in order to determine whether polymerization of actin affects oxidase activation. Cytosolic phalloidin prevented the depolymerization of actin following stimulation with fmlp, which was consequently “clamped” in the polymerized form during oxidase activation. Under these conditions oxidase activation was inhibited, the extent of inhibition being related to the level of polymerization at which the actin was “clamped”. It was concluded that the actin polymerization which accompanies stimulation with fmlp interacts with other intracellular signals to limit oxidase activation.

AL-SAMARIEE AI, SHAKER, K. AM, and AL-BASSOMY MA (1988). RESIDUE LEVELS OF THREE ORGANOPHOSPHORUS INSECTICIDES IN SWEET PEPPER GROWN IN COMMERCIAL GREENHOUSES. PESTIC SCI; 22 189-194.
Chem Codes: Chemical of Concern: DZ Rejection Code: FATE.

BIOSIS COPYRIGHT: BIOL ABS. RRM DIAZINON PIRIMIPHOS-METHYL CHLORPYRIFOS INFLORESCENCE FOOD RESIDUE Ecology/ Plants/ Biochemistry/ Food Technology/ Fruit/ Nuts/ Vegetables/ Food Additives/Poisoning/ Food Additives/Toxicity/ Food Contamination/ Food Poisoning/ Food Preservatives/Poisoning/ Food Preservatives/Toxicity/ Air Pollution/ Soil Pollutants/ Water Pollution/ Biophysics/ Plants/Physiology/ Plants/Metabolism/ Plants/Anatomy & Histology/ Reproduction/ Vegetables/ Herbicides/ Pest Control/ Pesticides/ Arachnida/ Entomology/Economics/ Plants/ Arachnida/ Entomology/Economics/ Insecticides/ Pest Control/ Pesticides/ Plants

Alabaster, J. S. (1969). Survival of Fish in 164 Herbicides, Insecticides, Fungicides, Wetting Agents and Miscellaneous Substances. Int.Pest Control 11: 29-35 (Author Communication Used).

EcoReference No.: 542

Chemical of Concern: 24DXY,ATZ,CMPH,DBN,DZ,PQT,SZ,ACL,DZM,TFN,TBT,PYZ,FUR,NaPCP,MCPP1; Habitat: A; Effect Codes: MOR; Rejection Code: NO CONTROL(ALL CHEMS).

ALAEE, M., FANG, X., YOUNG, S., TODD, A., STRUGER, J., HARRIS, M., and BESTARI, K. (1998). THE ANALYSIS OF ORGANOPHOSPHOROUS PESTICIDES IN SURFACE WATER USING SOLID-PHASE DISK EXTRACTION AND GC-MS. INTERNATIONAL ASSOCIATION FOR GREAT LAKES RESEARCH. 41ST CONFERENCE OF THE INTERNATIONAL ASSOCIATION FOR GREAT LAKES RESEARCH; MEETING, HAMILTON, ONTARIO, CANADA, MAY 18-22, 1998. 160P. INTERNATIONAL ASSOCIATION FOR GREAT LAKES RESEARCH: ANN ARBOR, MICHIGAN, USA.; 0 137.

Chem Codes: Chemical of Concern: DZ Rejection Code: ABSTRACT.

BIOSIS COPYRIGHT: BIOL ABS. RRM MEETING ABSTRACT MEETING POSTER SURFACE WATER ORGANOPHOSPHOROUS PESTICIDES POLLUTANT SOLID-PHASE DISK EXTRACTION GC-MS DIAZINON AZINPHOS-METHYL POLLUTION LABORATORY METHOD Congresses/ Biology/ Air Pollution/ Soil Pollutants/ Water Pollution